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CORD-19:00adbbcc70c39794b7d91a479943c84cc33db30a JSONTXT 9 Projects

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Id Subject Object Predicate Lexical cue
T1 0-56 Sentence denotes IMMUNOLOGY AND PREVENTION OF INFECTION IN FEEDLOT CATTLE
T2 58-66 Sentence denotes Abstract
T3 69-80 Sentence denotes mechanisms.
T4 81-151 Sentence denotes The acquired immune system can be stimulated by effective vaccination.
T5 152-283 Sentence denotes It takes 1 to 2 weeks after vaccination or exposure to the virulent organism before the acquired immune system is fully functional.
T6 284-509 Sentence denotes Maintaining optimal immune function for the prevention of infectious diseases requires good management practices to prevent suppression of the immune system and sound vaccination practices to induce optimal acquired immunity.
T7 510-820 Sentence denotes This article briefly reviews the basic types of immunity, the factors relevant to feedlot cattle that have been shown to suppress immune function, and what is known about the basis of protective acquired immunity against the common bovine respiratory pathogens that cause significant losses in feedlot animals.
T8 821-976 Sentence denotes The native defense mechanisms include enzymes in the saliva and tears, acids in the stomach, fatty acids in the skin, and normal flora at mucosal surfaces.
T9 977-1126 Sentence denotes Native defense mechanisms also include the complement system and phagocytic white blood cells which are capable of killing some bacteria and viruses.
T10 1127-1263 Sentence denotes These native defense mechanisms are functional immediately when an infectious agent enters the body even if an animal is not vaccinated.
T11 1264-1361 Sentence denotes The complement system and phagocytic cells work more efficiently in a vaccinated animal, however.
T12 1362-1507 Sentence denotes Those bacteria and viruses that are capable of producing disease have evolved ways to avoid being easily killed by the native defense mechanisms.
T13 1508-1783 Sentence denotes In order for an animal to be adequately protected from economically important infectious diseases, it must have either been previously exposed to the disease or vaccinated against the disease so that it developed humoral immunity, cell-mediated immunity, or mucosal immunity.
T14 1784-1883 Sentence denotes Humoral immunity is due to the presence of either immunoglobulin G (IgG) or IgM in the bloodstream.
T15 1884-1993 Sentence denotes When an animal is vaccinated, B lymphocytes respond to the vaccine by producing IgM-and IgG-class antibodies.
T16 1994-2151 Sentence denotes These antibodies are proteins that circulate in the bloodstream and can attach to the infectious agent when it is encountered in the blood or in the tissues.
T17 2152-2214 Sentence denotes Antibodies alone are not capable of killing infectious agents.
T18 2215-2286 Sentence denotes The presence of circulating IgG and IgM may help to control disease by:
T19 2287-2290 Sentence denotes 1 .
T20 2291-2433 Sentence denotes Agglutinating infectious agents, thereby reducing the number of infectious particles (for viruses) and facilitating removal by phagocytosis 2.
T21 2434-2471 Sentence denotes Binding to and neutralizing toxins 3.
T22 2472-2547 Sentence denotes Binding to the infectious agent and blocking attachment to cell surfaces 4.
T23 2548-2642 Sentence denotes Binding to the infectious agent and initiating the classic pathway of complement activation 5.
T24 2643-2705 Sentence denotes Opsonizing infectious agents and facilitating phagocytosis 6 .
T25 2706-2983 Sentence denotes Mediating attachment of cytotoxic cells to the surface of infected cells so that the infected cells may be destroyed by antibody-dependent cellmediated cytotoxicity Some disease-causing organisms, however, are resistant to control by these activities of circulating antibodies.
T26 2984-3108 Sentence denotes These organisms must be attacked and destroyed by the cell-mediated immune system or controlled by the secretory IgA system.
T27 3109-3196 Sentence denotes The term cell-mediated immunity refers to immunity mediated primarily by T lymphocytes.
T28 3197-3274 Sentence denotes The T lymphocytes have two basic methods for protecting animals from disease.
T29 3275-3456 Sentence denotes Some lymphocytes called "cytotoxic T cells" make contact with cells presenting foreign antigens on their surface such as viral antigens or antigens from some intracellular bacteria.
T30 3457-3560 Sentence denotes The T cells specifically recognize the foreign antigens and kill the cell that has them on its surface.
T31 3561-3622 Sentence denotes This effectively prevents virus from replicating in the cell.
T32 3623-3701 Sentence denotes The second method that T cells use to fight infection is to secrete cytokines.
T33 3702-3808 Sentence denotes Cytokines are glycoprotein molecules that activate other cells of the immune system to be more aggressive.
T34 3809-3880 Sentence denotes This includes macrophages, neutrophils, and natural killer lymphocytes.
T35 3881-4074 Sentence denotes The activated macrophages and neutrophils are more efficient at killing bacteria, especially facultative intracellular bacterial pathogens like brucella, mycobacteria, salmonella, and listeria.
T36 4075-4161 Sentence denotes The activated natural killer cells are more efficient at killing virus-infected cells.
T37 4162-4300 Sentence denotes The T cells that secrete cytokines to enhance killing by macrophages, neutrophils, and natural killer cells are called "T-helper I" cells.
T38 4301-4430 Sentence denotes T lymphocytes are also essential for secreting cytokines which control the type and amount of antibody produced by B lymphocytes.
T39 4431-4476 Sentence denotes These T cells are called liT-helper 2" cells.
T40 4477-4556 Sentence denotes Therefore, production of a normal antibody response requires T-Iymphocyte help.
T41 4557-4657 Sentence denotes The activity of the T-helper 2 cells is not usually considered to be part of cell-mediated immunity.
T42 4658-4849 Sentence denotes Protecting the animal from infection on mucosal surfaces such as the intestinal tract, respiratory tract, mammary glands, and reproductive tract is especially difficult for the immune system.
T43 4850-5111 Sentence denotes The antibodies responsible for humoral immunity and the white blood cells responsible for cell-mediated immunity are found in the bloodstream and in the tissues to some extent, including submucosal surfaces; however, they are not found on some mucosal surfaces.
T44 5112-5260 Sentence denotes Therefore, they can help to prevent invasion through the mucosal surface but are not very effective at controlling infection on the mucosal surface.
T45 5261-5571 Sentence denotes On some mucosal surfaces such as the lower respiratory tract, reproductive tract, and mammary gland, where IgG and white blood cells are found in relative abundance, they are able to provide a significant amount of protection, but they are not able to function as effectively as in the bloodstream and tissues.
T46 5572-5778 Sentence denotes Protection on mucosal surfaces is due, in large part, to a special class of antibody called "secretory IgA." Secretory IgA tends to be produced in response to pathogens that enter through a mucosal surface.
T47 5779-5900 Sentence denotes Secretory IgA is secreted onto mucosal surfaces, where it may bind to mucus and be present in fairly high concentrations.
T48 5901-6036 Sentence denotes Secretory IgA is resistant to destruction by the proteolytic enzymes on mucosal surfaces that are capable of breaking down IgA and IgM.
T49 6037-6198 Sentence denotes IgA is the predominant immunoglobulin found in the milk of monogastrics and is important for protecting the gastrointestinal tract of the neonate from pathogens.
T50 6199-6324 Sentence denotes In ruminants, IgGl is the predominant class of antibody in the milk for protecting the gastrointestinal tract of the newborn.
T51 6325-6411 Sentence denotes Mucosal surfaces of ruminants tend to have high concentrations of IgGl as well as IgA.
T52 6412-6597 Sentence denotes The bovine respiratory disease (BRD) complex has been extensively investigated in recent years, and numerous vaccines and antibiotics have been developed and prescribed for its control.
T53 6598-6713 Sentence denotes Despite these efforts, BRD is still a major problem, and its pathogenesis and etiology are incompletely understood.
T54 6714-6876 Sentence denotes Respiratory disease is particularly prevalent during the first 45 days after calves have been weaned, transported, and placed in a feedlot (i.e., shipping fever).
T55 6877-7091 Sentence denotes 49 The economically important clinical signs, lesions, and death loss in shipping fever usually can be attributed to bacterial pneumonia due to Pasteurella haemolytica, Pasteurella multocida, or Haemophilus somnus.
T56 7092-7172 Sentence denotes These bacteria are commonly found in the nasopharyngeal area of healthy animals.
T57 7173-7283 Sentence denotes Under normal conditions, the bacteria are unable to move into the lower respiratory tract and cause pneumonia.
T58 7284-7433 Sentence denotes In fact, the lungs of normal healthy cattle can withstand a challenge with surprisingly large numbers of these bacteria without serious consequences.
T59 7434-7618 Sentence denotes If the animal is stressed, however, has a respiratory viral infection, or is otherwise immunosuppressed, a severe pneumonia can be established by a relatively small number of bacteria.
T60 7619-7933 Sentence denotes These observations have led to the concept that BRD has a multifactorial etiology involving a complex interaction between stressors, viruses, and perhaps other immunosuppressive factors that act separately or together to suppress the defense mechanisms in the lung and predispose the animal to bacterial pneumonia.
T61 7934-8167 Sentence denotes There is ample evidence that environmental, physical, or psychologic stress (distress) can lead to increased susceptibility to disease and that the increased susceptibility is at least partially due to alterations in immune function.
T62 8168-8391 Sentence denotes 54, 55 A general bodily response to distress is the release of adrenocorticotropin from the anterior pituitary gland, which stimulates the adrenal cortex to increase the synthesis and secretion of cortisol (hydrocortisone).
T63 8392-8487 Sentence denotes Cortisol is responsible for many (but not all) of the effects of distress on the immune system.
T64 8488-8644 Sentence denotes Several stressors that are sometimes associated with the introduction of cattle to a feedlot have been proven to result in increased plasma cortisol levels.
T65 8645-8763 Sentence denotes These conditions include castration and dehorning, weaning, handling, forced exercise, acute pain, and transportation.
T66 8764-9112 Sentence denotes 2 , 23, 41, 97, 99,102 There is evidence that high plasma cortisol concentrations affect several aspects of host defense,89 including decreased antibody response to primary immunization, decreased lymphocyte function leading to impaired cell-mediated immunity, and an inhibition of phagocytic cell ability to enter the tissues and destroy bacteria.
T67 9113-9260 Sentence denotes The levels of endorphins, catecholamines, insulin, glucagon, growth hormone, prolactin, thyroid hormones, and melatonin are also altered by stress.
T68 9261-9398 Sentence denotes These hormones may alter immune function as well, but their effects on the immune system are not understood as well as those of cortisol.
T69 9399-9618 Sentence denotes A very important effect of elevated cortisol concentration or the administration of pharmacologic doses of glucocorticoids (e.g., dexamethasone) is the recrudescence of herpesviruses such as bovine herpesvirus 1 (BHVl).
T70 9619-9767 Sentence denotes BHVI can be recrudesced in otherwise healthy cattle by stress or dexamethasone treatment; this can be done even if the animal has an antibody titer.
T71 9768-9888 Sentence denotes The recrudescence of a latent BHVI infection in an animal under stress can lead to the spread of BHVI throughout a herd.
T72 9889-10007 Sentence denotes Like other herpesviruses, BHVI is harbored in a latent state in animals that have recovered from an initial infection.
T73 10008-10123 Sentence denotes Even a modified live virus (MLV) vaccine strain can be recrudesced and shed under the influence of glucocorticoids.
T74 10124-10289 Sentence denotes 80 One clinical application of dexamethasone has been in the treatment of cattle suffering from bronchial pneumonia to reduce the inflammatory response in the lungs.
T75 10290-10819 Sentence denotes A short-term improvement in clinical signs often occurs; however, experimentation has shown that when dexamethasone administration was combined with antibacterial and antihistamine therapy for the treatment of bronchial pneumonia in cattle, the outcome was a poorer response to treatment, more relapses, and greater death losses.· This occurred because in decreasing the inflammatory response in the lung, the dexamethasone also impaired the activity of the host defense mechanisms, thus allowing increased bacterial replication.
T76 10820-11084 Sentence denotes 17 In general, glucocorticoids should not be used as a part of the treatment regimen for BRD unless the inflammatory response in the lung is life threatening or the clinician is confident that the antimicrobial agent being used can control the bacterial infection.
T77 11085-11474 Sentence denotes The best evidence that viruses play an important role in predisposing to bacterial pneumonia comes from epidemiologic data indicating that a recent serologic conversion to a respiratory virus is associated with bacterial pneumonia and from challenge experiments in which cattle are infected with a virus and then infected a few days later with an aerosol of P. haemolytica or P. multocida.
T78 11475-11726 Sentence denotes 90 The cattle that are preinfected with either BHVl, parainfluenza 3 (PI3) virus, or bovine viral diarrhea (BVD) virus develop a severe bacterial pneumonia, although the nonvirus-infected control cattle are able to clear the bacteria from their lungs.
T79 11727-11953 Sentence denotes These viruses may have a number of effects on the antibacterial defense mechanisms in the lung, including impairment of mucociliary clearance, suppression of phagocytic cell function, and interference with lymphocyte function.
T80 11954-12130 Sentence denotes The relative importance of each of these effects is not known, but it is probably a combination of activities that is responsible for the predisposition to bacterial pneumonia.
T81 12131-12316 Sentence denotes Studies have shown that simultaneous infection with BVD virus and bovine respiratory syncytial virus (BRSV) can synergistically increase the pathologic effects of each individual virus.
T82 12317-12596 Sentence denotes 57 A number of respiratory viruses of cattle can inhibit mucociliary clearance in the ciliated respiratory epithelium (e.g., BHVl, PI3 virus, BVD virus, BRSV).90 Decreased mucociliary clearance is often cited as a primary reason for greater susceptibility to bacterial pneumonia.
T83 12597-12712 Sentence denotes Evidence suggests, however, that this is not as important as impairment of bactericidal mechanisms within the lung.
T84 12713-13054 Sentence denotes This conclusion is based on the observations that the rate of bacterial killing within the healthy lung greatly exceeds the rate of mucociliary transport out of the lungs and that the period of increased susceptibility to bacterial pneumonia does not coincide with the timing of the inhibition of mucociliary clearance after viral infection.
T85 13055-13261 Sentence denotes 48 The current consensus seems to be that suppression of the function of phagocytic cells in the lungs (both alveolar macrophages and neutrophils) is a primary factor in predisposing to bacterial infection.
T86 13262-13401 Sentence denotes The phagocytic cells are essential for killing bacteria that find their way to the lower respiratory tract and removing them from the lung.
T87 13402-13583 Sentence denotes The alveolar macrophage is the predominant phagocyte in the healthy lung and is very important in surveillance and removal of foreign material (including bacteria) from the alveoli.
T88 13584-13843 Sentence denotes If the alveolar macrophages are unable to control the infection or if the lung is exposed to a large challenge dose of bacteria, neutrophils migrate into the alveoli and bronchioles rapidly, and they soon (within a few hours) become the predominant cell type.
T89 13844-14116 Sentence denotes Neutrophils are quite active phagocytic ally and have potent bactericidal mechanisms, including the generation of toxic oxygen products (e.g., hydrogen peroxide, superoxide anion, hydroxyl radical) and the release of cationic antibacterial peptides and hydrolytic enzymes.
T90 14117-14200 Sentence denotes In addition to being bactericidal, these products also can damage pulmonary tissue.
T91 14201-14326 Sentence denotes If the infection is not brought under control relatively rapidly, the neutrophils can induce considerable damage in the lung.
T92 14327-14432 Sentence denotes There is evidence that BHVl, PI3 virus, BVD virus, and BRSV can each impair alveolar macrophage function.
T93 14433-14492 Sentence denotes 9o BHVl and BVD virus also can inhibit neutrophil function.
T94 14493-14589 Sentence denotes 90 The effects of PI3 virus and BRSV on neutrophil function apparently have not been determined.
T95 14590-14726 Sentence denotes An important aspect of alveolar macrophage and neutrophil function is that they can be activated by cytokines secreted by T lymphocytes.
T96 14727-14852 Sentence denotes When these phagocytes are activated, they become more "aggressive" and are more effective at controlling bacterial infection.
T97 14853-15029 Sentence denotes By interfering with lymphocyte function, the BRD viruses may inhibit alveolar macrophage and neutrophil activation and leave the animal more susceptible to bacterial pneumonia.
T98 15030-15321 Sentence denotes The BVD virus has been shown to inhibit aspects of lymphocyte,51, 82,93 macrophage,59 and neutrophil 92 ,93 function; to impair bacterial clearance from the blood 87 ; to lessen the ability of calves to clear BHVI from the lung 84 ; and to facilitate pulmonary infection with P. haemolytica.
T99 15322-15449 Sentence denotes 83 At least one MLV vaccine strain of BVD virus also was shown to be capable of suppressing lymphocyte and neutrophil function.
T100 15450-15568 Sentence denotes 91 The suppression of neutrophil function lasts for 3 to 4 weeks after infection with either a virulent or MLV strain.
T101 15569-15990 Sentence denotes Cattle that were given adrenocorticotrophin to increase their serum cortisol levels at the same time that they received MLV BVD vaccine had more marked suppression of neutrophil function than cattle that received either the modified live BVD virus or the adrenocorticotrophin only.91 This implies that stress and the BVD virus act synergistically to cause an immunosuppression that is worse than either would cause alone.
T102 15991-16082 Sentence denotes The clinical importance of immunosuppression by currently used MLV BVD vaccines is unknown.
T103 16083-16174 Sentence denotes It is probably not a problem when used in healthy animals under good management conditions.
T104 16175-16309 Sentence denotes The bovine immunodeficiency virus (BIV) is a lentivirus that has antigenic and genetic homology with the human immunodeficiency virus.
T105 16310-16389 Sentence denotes The true prevalence of BIV infection of cattle in the United States is unknown.
T106 16390-16461 Sentence denotes Various serologic surveys have detected infection rates from 4% to 18%.
T107 16462-16650 Sentence denotes 105 Experimental infection with BIV has been associated with changes in circulating lymphocyte numbers, 15 alterations in monocyte function,77, 95, 96 and decreases in neutrophil function.
T108 16651-16814 Sentence denotes 31 , 32 These changes were relatively minor, however, and experimental BIV infection has not been shown to lead to a clinically apparent immunodeficiency syndrome.
T109 16815-16943 Sentence denotes The potential impact of naturally occurring infection with BIV on susceptibility to diseases in feedlot cattle is still unknown.
T110 16944-17126 Sentence denotes Several other viruses have been associated with the BRD complex, including bovine adenovirus, coronavirus, DN599 herpesvirus (Movar), rhinoviruses, reoviruses, and bovine parvovirus.
T111 17127-17338 Sentence denotes 90, 104 Little is known about the immunosuppressive effects of these viruses in cattle; however, it is logical to assume that infection with any of them may render cattle more susceptible to bacterial pneumonia.
T112 17339-17466 Sentence denotes Mycoplasma species (Mycoplasma hovis, Mycoplasma dispar, and ureaplasmas) also may be important factors in the etiology of BRD.
T113 17467-17579 Sentence denotes Infection with these agents that is uncomplicated by any other factors usually results in subclinical pneumonia.
T114 17580-17713 Sentence denotes The mycoplasmas probably playa larger role in BRD as predisposing factors to secondary bacterial infection than as primary pathogens.
T115 17714-17822 Sentence denotes 101 Infection with M. bovis has been reported to enhance the severity of pneumonia caused by P. haemolytica.
T116 17823-18111 Sentence denotes 46 The mechanisms by which mycoplasmas predispose to secondary infection are not clear, but induction of inflammation, impairment of lymphocyte function, inhibition of mucociliary transport, and inhibition of neutrophil function all have been suggested as possible contributing factors.90
T117 18112-18207 Sentence denotes Nutrition plays an important role in maintaining optimal immune function and resistance to BRD.
T118 18208-18263 Sentence denotes This topic is covered in another article in this issue.
T119 18264-18513 Sentence denotes Immunosuppression due to the administration of glucocorticoids to cattle has been shown to exacerbate clinical signs of coccidiosis?6 In addition, there is evidence that coccidiosis itself is immunosuppressive and predisposes to secondary infection.
T120 18514-18694 Sentence denotes The feeding of coccidiostats to feedlot cattle has been associated with reduced shedding of coccidial oocysts and with reduced morbidity65 and mortality33 from respiratory disease.
T121 18695-18794 Sentence denotes Subclinical and clinical coccidiosis has also been shown to suppress neutrophil function in cattle.
T122 18795-18929 Sentence denotes 94 Substances secreted by nematodes progressing through larval stages have been shown to suppress proliferation of bovine lymphocytes.
T123 18930-19090 Sentence denotes 36 Therefore, controlling coccidiosis and parasites in feedlot cattle is important for maintaining optimal immune function and resistance to infectious disease.
T124 19091-19184 Sentence denotes BHVl, also referred to as "infectious bovine rhinotracheitis" (IBR), is an alpha herpesvirus.
T125 19185-19296 Sentence denotes The characteristics of protective immunity against BHVI are similar to those against other alpha herpesviruses.
T126 19297-19402 Sentence denotes Antibody titers as measured by a serum neutralization (SN) test can protect the animal against infection.
T127 19403-19554 Sentence denotes The evidence for this is that the passive antibodies that a calf receives from the colostrum can provide solid protection against infectious challenge.
T128 19555-19664 Sentence denotes The passively acquired antibody can also prevent an MLV vaccine from inducing an antibody response in a calf.
T129 19665-19774 Sentence denotes This maternal antibody blockage of an MLV vaccine can even occur if the serum neutralizing titer is very low.
T130 19775-19958 Sentence denotes If the calf receives a lot of colostrum with a high titer against BHV1, it may be 6 to 8 months old before it is capable of responding to an MLV vaccine by the production of antibody.
T131 19959-20279 Sentence denotes Even though the MLV vaccine may not induce an antibody response, it is possible that it may induce a memory response in the face of maternal antibody so that if the calf is subsequently exposed to the virulent virus, it may be capable of responding more rapidly to the viral challenge and have some degree of protection.
T132 20280-20505 Sentence denotes There is evidence to indicate that vaccination in the presence of maternal antibody against pseudorabies virus in pigs (another alpha herpesvirus) stimulates immunologic memory even though an antibody response does not occur.
T133 20506-20633 Sentence denotes This immunologic memory has been shown to provide partial protection against disease challenge with pseudorabies virus in pigS.
T134 20634-20770 Sentence denotes 111 There is also evidence that the same is likely to be true for MLV BHVl vaccines used in the presence of maternal antibody in calves.
T135 20771-20934 Sentence denotes 30 ,70 An important characteristic of herpesviruses is that after an animal recovers from disease, it is latently infected with the virus for the rest of its life.
T136 20935-20995 Sentence denotes The virus resides in ganglia of nerves in a quiescent state.
T137 20996-21059 Sentence denotes Even MLV BHVl vaccine has been shown to latently infect cattle.
T138 21060-21130 Sentence denotes 3o The immune system is not capable of clearing this latent infection.
T139 21131-21314 Sentence denotes If the animal is stressed or treated with glucocorticoids later in life, the virus is likely to recrudesce and be shed even if the animal has a high serum neutralizing antibody titer.
T140 21315-21457 Sentence denotes 30, 93, 106 Therefore, serum neutralizing antibody can prevent infection, but it cannot prevent recrudescence and shedding of the latent BHVl.
T141 21458-21600 Sentence denotes The latently infected animal that is shedding BHVl may not show any clinical signs but is a source of infection for other animals in the herd.
T142 21601-21742 Sentence denotes Once an infection with BHVl is established, a cell-mediated immune response is probably needed in order to bring the infection under control.
T143 21743-21824 Sentence denotes Cytotoxic T lymphocytes are thought to be important in controlling the infection.
T144 21825-21903 Sentence denotes There do not seem to be important antigenic differences between BHVl isolates.
T145 21904-22035 Sentence denotes Immunity to one isolate of BHVl or one vaccine strain of virus appears to provide good cross protection against all field isolates.
T146 22036-22167 Sentence denotes Therefore, an SN titer measured against any BHVl virus in the laboratory will more or less equally neutralize any other BHVl virus.
T147 22168-22385 Sentence denotes An antibody titer determined by enzyme-linked immunosorbent assay may or may not measure protective (serum neutralizing) antibodies depending on the nature of the antigen used in the enzyme-linked immunosorbent assay.
T148 22386-22637 Sentence denotes SN antibody titers approximately greater than 1 to 32 have been shown to protect against disease induced by BVD virus. ll A major problem, however, in immunity to BVD virus is that there is a great deal of antigenic diversity among BVD virus isolates.
T149 22638-22776 Sentence denotes 27 The BVD virus, like most other RNA viruses, has a high mutation rate, resulting in almost unlimited antigenic diversity among isolates.
T150 22777-22823 Sentence denotes The E2 gene of BVD codes for the CPS3 protein.
T151 22824-22909 Sentence denotes This is the major surface glycoprotein and is immunodominant for antibody production.
T152 22910-22957 Sentence denotes It is a major epitope for virus neutralization.
T153 22958-23038 Sentence denotes The E2 gene represents one of the hypervariable regions of the BVD virus genome.
T154 23039-23117 Sentence denotes This hypervariability may be due to selective pressure from the immune system.
T155 23118-23376 Sentence denotes 26 The heterogeneity of the CPS3 protein (and other less important virus neutralizing epitopes) limits the ability of an antibody response to one strain of BVD virus to protect against a wide array of other possible strains that the animal may be exposed to.
T156 23377-23514 Sentence denotes The SN antibody titer of a single serum sample may vary from 10-to 100-fold depending on which BVD virus isolate is used in the SN assay.
T157 23515-23739 Sentence denotes 12, 27 The animal is probably protected against the isolates that the serum can neutralize at a titer of approximately 1 to 32 or greater, but the antibody in the serum cannot protect against the other isolates of BVD virus.
T158 23740-23860 Sentence denotes In a field outbreak, it is impossible to predict which antigenic type of BVD virus the animal is going to be exposed to.
T159 23861-24101 Sentence denotes There is apparently no single vaccine strain of BVD virus (or even a combination of vaccine strains) that is capable of providing cross-protective SN antibody titers against all potential virulent BVD virus isolates that may be encountered.
T160 24102-24253 Sentence denotes Little is known about the role of cell-mediated immunity (either cytotoxic T cells or T-helper 1 cells) in protection against BVD virusinduced disease.
T161 24254-24336 Sentence denotes It is likely that cell-mediated immunity is important for recovery from infection.
T162 24337-24538 Sentence denotes It is quite possible that cell-mediated immunity, especially that provided by cytotoxic T lymphocytes, provides better cross-protective immunity between different BVD virus isolates than antibody does.
T163 24539-24658 Sentence denotes If this is true, an animal that has developed cell-mediated immunity has better protection against BVD virus challenge.
T164 24659-24841 Sentence denotes Because MLV vaccines are more likely to induce cytotoxic T lymphocytes than are killed vaccines, they may provide better cross-protective immunity to a variety of BVD virus isolates.
T165 24842-25012 Sentence denotes This hypothesis fits the commonly held perception that MLV vaccines provide better immunity to BVD virus than killed vaccines, but it remains to be proven experimentally.
T166 25013-25098 Sentence denotes Recently, two separate genotypes of BVD virus have been defined,88 type 1 and type 2.
T167 25099-25197 Sentence denotes The type-2 BVD viruses have the potential to produce severe acute infection even in adult animals.
T168 25198-25312 Sentence denotes The homologous genotypes tend to induce better cross-neutralizing antibody titers than the heterologous genotypes.
T169 25313-25492 Sentence denotes A type-l MLV BVD vaccine has been shown to provide protection from a virulent challenge with a type-2 BVD virus/ 2 probably due to cross-protective cell-mediated immune responses.
T170 25493-25692 Sentence denotes A critical factor in controlling BVD virus infection in a herd, and probably in the cattle population as a whole, is to prevent infection of the fetus and development of persistently infected calves.
T171 25693-25854 Sentence denotes There are scant data on the ability of vaccines administered to the cow to prevent infection of the fetus if the cow should become exposed to virulent BVD virus.
T172 25855-26013 Sentence denotes There have been some experiments conducted using killed BVD virus vaccines in cows that were subsequently challenged with virulent BVD virus during pregnancy.
T173 26014-26105 Sentence denotes In most cases, these vaccines did not provide adequate immunity to prevent fetal infection.
T174 26106-26233 Sentence denotes In one experiment using three doses of a killed vaccine, evidence of fetal protection from experimental challenge was obtained.
T175 26234-26603 Sentence denotes 13 Considering all of the evidence, it is likely that a killed vaccine inducing a titer of greater than 1 to 32 in the cow against a particular isolate of BVD virus can protect the fetus from becoming infected; however, there are likely to be strains of BVD virus that are antigenic ally different from the vaccine virus, which the cow and fetus are not protected from.
T176 26604-26775 Sentence denotes It is possible that an MLV vaccine administered to the cow prior to pregnancy may provide better crossprotective immunity against a variety of isolates as described above.
T177 26776-26939 Sentence denotes Nevertheless, the authors are unaware of any experiments demonstrating that an MLV vaccine administered to a cow is capable of protecting the fetus from infection.
T178 26940-27066 Sentence denotes Fetal protection experiments are expensive to perform but are needed to answer important questions regarding vaccine efficacy.
T179 27067-27156 Sentence denotes Circulating antibody does not seem to provide good immunity against BRSV-induced disease.
T180 27157-27392 Sentence denotes The evidence for this is the observation that calves with passive antibody are not usually protected from BRSVinduced infection or disease; however, calves that recover from disease are protected from reinfection, at least for a while.
T181 27393-27652 Sentence denotes 60 The nature of protective immunity is not clearly understood, but there is some evidence to suggest that a strong IgA memory response is associated with protection and that a cytotoxic T-Iymphocyte response to the F protein of BRSV may protect from disease.
T182 27653-27958 Sentence denotes In one series of experiments in which calves with and without maternal antibody were primed with live BRSV via the respiratory tract, protection was associated with a strong and rapid mucosal antibody memory response after challenge but not with serum or mucosal antibody present at the time of challenge.
T183 27959-28160 Sentence denotes 61 A problem with BRSV vaccination and immunity is that maternal antibody does not provide good protection, but it does interfere with active immunization of the calf as assayed by antibody production.
T184 28161-28313 Sentence denotes 6o This presents a real problem, because BRSV tends to cause disease in calves that are too young to effectively vaccinate because of maternal antibody.
T185 28314-28514 Sentence denotes Additional research is needed to further characterize the nature of protective immunity to BRSV and to develop vaccines that can effectively immunize a young calf in the presence of maternal antibody.
T186 28515-28995 Sentence denotes In recent years it has been shown that antibody against P. haemolytica leukotoxin and surface capsular antigens is important to help protect calves against P. haemolytica-induced pneumonia. lB , 19,37,72 When measuring antibody titers against P. haemolytica, it would be best to measure both the antileukotoxin antibody titer and the anticapsular antibody titer, because these titers correlate best with immunity when a calf is directly challenged in the lung with P. haemolytica.
T187 28996-29225 Sentence denotes Lymphocytes from mediastinal lymph nodes of calves vaccinated with an MLV P. haemolytica vaccine or recovered from P. haemolytica challenge secreted gamma interferon when stimulated with outer membrane proteins of P. haemolytica.
T188 29226-29328 Sentence denotes This is an indication that calves develop T-helper 1 cell-mediated immune responses to P. haemolytica.
T189 29329-29487 Sentence denotes Protection against pneumonic lesions more closely correlated with antileukotoxin antibody responses than with lymphocyte gamma interferon production, however.
T190 29488-29629 Sentence denotes 25 An important component in the pathogenesis of naturally occurring P. haemolytica pneumonia is colonization of the upper respiratory tract.
T191 29630-29737 Sentence denotes 34 P. haemolytica can be isolated in low numbers from the upper respiratory tract of normal healthy calves.
T192 29738-29911 Sentence denotes Viral infection or stress may allow the P. haemolytica in the nasal and pharyngeal areas to grow to large numbers, leading to inhalation of microcolonies deep into the lung.
T193 29912-30025 Sentence denotes These microcolonies then may successfully avoid the immune defenses in the alveolus and produce severe pneumonia.
T194 30026-30153 Sentence denotes Little is known about the ability of current vaccines to inhibit colonization of the upper respiratory tract by P. haemolytica.
T195 30154-30301 Sentence denotes Further research is needed to design and test vaccines that are capable of preventing or reducing upper respiratory colonization by P. haemolytica.
T196 30302-30391 Sentence denotes Not much is known about the nature of protective immunity to H. somnus-induced pneumonia.
T197 30392-30555 Sentence denotes H. somnus has a number of potential virulence factors that have been studied, including endotoxin, antibody binding proteins, surface nucleotides, and a hemolysin.
T198 30556-30762 Sentence denotes 2l , 112, 114 It is likely that antibody against these potential virulence factors may help to protect the calf against H. somnus-induced pneumonia; however, there are scant data to support this hypothesis.
T199 30763-31095 Sentence denotes In addition, there are two proteins that have been isolated from H. somnus, a 40-kD protein and a 31-kD protein, that have been implicated as important antigens for inducing immunity.3B, 113 The role of T-helper 1 cells or a secretory IgA response in protection from H. somnus-induced pneumonia has not been thoroughly investigated.
T200 31096-31265 Sentence denotes There is evidence that gamma interferon, which can be produced during aT-helper 1 cell immune response, can help to protect the calf against H. somnus-induced pneumonia.
T201 31266-31268 Sentence denotes 16
T202 31269-31306 Sentence denotes We use both live and killed vaccines.
T203 31307-31372 Sentence denotes The advantages of one are usually the disadvantages of the other.
T204 31373-31739 Sentence denotes MLV vaccine attributes include strong long-lasting immune response achieved with fewer doses, less reliance on adjuvants, possible stimulation of interferon production, stimulation of the effector component of cell-mediated immunity (cytotoxic T lymphocytes), and the fact that the bacteria or virus may look and behave more like the pathogenic form of the organism.
T205 31740-31897 Sentence denotes Some advantages of killed vaccines are that they are more stable in storage and are unlikely to cause disease as a result of residual virulence or reversion.
T206 31898-31988 Sentence denotes Numerous brands of vaccines provide a variety of combinations of live and killed antigens.
T207 31989-32082 Sentence denotes These include IBR virus, BVD virus, PI3 virus, BRSV, Pasteurella sp., and H. somnus antigens.
T208 32083-32257 Sentence denotes IBR virus vaccines are available in MLV form for intramuscular, subcutaneous, or intranasal use as well as in killed and chemically altered virus forms for intramuscular use.
T209 32258-32373 Sentence denotes Intramuscular MLV vaccines are thought to quickly induce immunity following proper administration of a single dose.
T210 32374-32515 Sentence denotes Intranasal MLV vaccines induce immunity at the mucosal surface through stimulation of acquired mucosal immunity and production of interferon.
T211 32516-32646 Sentence denotes They may be used safely in calves suckling pregnant cows and can induce immunity in the face of residual maternal antibody titers.
T212 32647-32695 Sentence denotes They are, however, more difficult to administer.
T213 32696-32804 Sentence denotes Killed virus vaccines require two doses administered at a 14-to 28-day interval in order to induce immunity.
T214 32805-32944 Sentence denotes Along with higher cost and concerns about shorter duration of immunity, this makes them less practical to use in a typical feedlot setting.
T215 32945-33187 Sentence denotes In a review of IBR virus vaccine clinical efficacy studies, results were positive or neutral; however, none were negative. s1 The studies date to 1958 and 1974 and may not apply to current cattle feeding management practices in North America.
T216 33188-33489 Sentence denotes In a field trial using IBR MLV vaccine at arrival, the incidence of upper respiratory disease was reduced from 17.2% in 3371 unvaccinated calves to 1 % in 3345 vaccinates (RR = 16; P<O.OOOO),us A well-designed trial using IBR MLV vaccine given on arrival failed to show benefits in health performance.
T217 33490-33637 Sentence denotes 24 Another report that failed to show IBR virus vaccine efficacy involved additional antigens and is discussed in the section on multiple antigens.
T218 33638-33732 Sentence denotes The current consensus is to include IBR virus in preconditioning and arrival vaccine regimens.
T219 33733-33885 Sentence denotes BVD virus vaccines are available in MLV and killed virus forms, and they are one of the most controversial vaccines used in cattle in the United States.
T220 33886-34201 Sentence denotes The lack of large-scale efficacy trials, widespread infection in the cattle population in the United States, the presence of persistently infected cattle that subsequently develop mucosal disease, and the emerging role of heterologous and novel strains of the virus all combine to create confusion and -controversy.
T221 34202-34245 Sentence denotes There is no clear consensus concerning use.
T222 34246-34494 Sentence denotes Measurements of certain immune parameters suggest that immunosuppression following use of MLV may be a concern 91 ; however, the lack of complications following its use in large numbers of cattle suggests that these may not be of practical concern.
T223 34495-34628 Sentence denotes 29 The use of MLV may be of greater concern in highly stressed cattle, but well-controlled studies evaluating this are not available.
T224 34629-34762 Sentence denotes As is the case with BHV1, dose and timing requirements of killed BVD virus vaccines are a severe limitation in most feedlot settings.
T225 34763-34997 Sentence denotes There are no reliable peer-reviewed reports of field trials examining the clinical effects of BVD virus vaccines in North American beef cattle based on research that uses scientifically valid methods with clinically relevant outcomes.
T226 34998-35088 Sentence denotes 81 Use is based on extrapolation from challenge or licensing data and personal preference.
T227 35089-35276 Sentence denotes A main concern with BVD is fetal infection with resulting abortion, congenital defects, or the development of persistently infected carriers that are a constant source of infective virus.
T228 35277-35487 Sentence denotes 4 , 10, 85 The virus can cross the placenta in susceptible pregnant cattle and result in fetal infection either through exposure to the field virus or through the improper use of intramuscular BVD MLV vaccines.
T229 35488-35591 Sentence denotes 108 If this occurs during the first 6 months of pregnancy, fetal losses or immune tolerance may result.
T230 35592-35717 Sentence denotes Fetal infection during the last trimester of gestation usually results in the birth of an immune, seropositive, healthy calf.
T231 35718-35973 Sentence denotes 62 Current information does not conclusively document the duration of protection following natural infection or the use of BVD MLV vaccine, although available information indicates that infection confers more than a single year of protection to the fetus.
T232 35974-36281 Sentence denotes 28 , 53, 58, 71, 85 Seronegative cattle vaccinated with BVD MLV vaccine in the last trimester of pregnancy had calves that seroconverted as fetuses, whereas over 90% of cattle that were seropositive had calves that did not, indicating that transplacental infection of previously exposed dams did not occur?8
T233 36282-36411 Sentence denotes Critical studies comparing the ability of BVD MLV and killed vaccines to protect the fetus in field situations are not available.
T234 36412-36744 Sentence denotes At the current time, it is believed that optimum protection of the beef breeding herd is dependent on active immunization with BVD MLV vaccine prior to breeding. lO , 28, 45, 53, 85 To ensure a response, the vaccine should be administered to replacement heifers two or more times between weaning (6 to 8 months of age) and breeding.
T235 36745-36871 Sentence denotes 10, 45, 53 The final injection should be at least 1 month before breeding in order to avoid detrimental effects on conception.
T236 36872-37037 Sentence denotes Although not documented, the use of different strains or serotypes of MLV vaccine for each injection has been proposed so as to expand the range of cross protection.
T237 37038-37174 Sentence denotes The genetic and antigenic instability of BVD virus may result in the emergence of isolates that have reduced antigenic cross reactivity.
T238 37175-37331 Sentence denotes 20, 56 The importance of the specificity of circulating antibody and effects on cellular immunity due to viral mutation are largely unanswered at this time.
T239 37332-37442 Sentence denotes A temperature-sensitive, BVD MLV vaccine was shown to be safe and to induce seroconversion in pregnant cattle.
T240 37443-37534 Sentence denotes 63 A killed Singer-strain vaccine prevented clinical signs following intrav~nous challenge.
T241 37535-37720 Sentence denotes 68 Pregnant cows vaccinated with a polyvalent killed BVD virus vaccine and challenged at 80 days of gestation showed resistance to fetal infections compared with nonvaccinated controls.
T242 37721-37883 Sentence denotes 43 The long duration of immunity and the cross protection between serotypes following the use of MLV vaccines make them preferable for use in beef breeding herds.
T243 37884-38011 Sentence denotes The opportunities for planned vaccination at noncritical stages of production and during times of minimal stress are available.
T244 38012-38116 Sentence denotes This makes infection from field strain viruses during critical periods of fetal development less likely.
T245 38117-38322 Sentence denotes If immunity has declined enough to permit natural infection, it may stimulate an immediate immune response without severe disease consequences, and this may be the basis for maintaining long-term immunity.
T246 38323-38485 Sentence denotes 53 Depending on the circumstances of each herd, annual, biannual, or less frequent MLV vaccine injections to cows between calving and breeding may be recommended.
T247 38486-38549 Sentence denotes BRSV vaccines are available in MLV and inactivated virus forms.
T248 38550-38743 Sentence denotes Because recovery from natural infection with respiratory syncytial virus does not engender protective immunity in most species, it is unlikely that vaccination can prevent subsequent infection.
T249 38744-38880 Sentence denotes Nevertheless, it may still be possible for vaccination to attenuate clinical signs of subsequent infections and reduce time to recovery.
T250 38881-39197 Sentence denotes One experimental challenge of a small number of calves showed that passive antibodies reduce the pathology associated with BRSV.8 Moreover, there are reports of improvement in gain and feed efficiency.3 Mixed results are reported from studies investigating clinical efficacy of BRSV vaccination of calves on arrival.
T251 39198-39420 Sentence denotes A statistically significant benefit of BRSV vaccination was shown in auction-or market-purchased and transported calves, with vaccinated calves being two times less likely to be treated for BRD complex (OR=2.0, P<O.OOOOl).
T252 39421-39536 Sentence denotes Freshly weaned and transported calves were 1.4 times less likely to be treated for BRD complex (OR = 1.4; P<O.OOl).
T253 39537-39655 Sentence denotes A statistically significant benefit of BRSV vaccination was not shown in the two classes of calves with low morbidity.
T254 39656-39999 Sentence denotes These included preconditioned calves (P = 0.11) and freshly weaned calves that were not transported (P = 0.75).42 In a Canadian study, results of five separate trials designed to assess BRSV vaccine efficacy were equivocal for calves vaccinated before weaning; however, reduction of treatment rate was reported in calves vaccinated on arrival.
T255 40000-40221 Sentence denotes No benefit was found for vaccination on arrival of yearling cattle.l1o Two additional trials involving calves 5 ,73 and one trial involving stocker cattle 50 failed to demonstrate a benefit of BRSV vaccination on arrival.
T256 40222-40357 Sentence denotes Although there is evidence to support BRSV vaccine usage in naive or mismanaged calves, inclusion in vaccine regimens is not universal.
T257 40358-40443 Sentence denotes Studies show that PI3 virus compromises the innate defenses of the respiratory tract.
T258 40444-40593 Sentence denotes 64 ,86 Because many older cattle arriving at feedlots are likely to be immune, the value of PI3 virus vaccination in yearling cattle is questionable.
T259 40594-40700 Sentence denotes Vaccination may be valuable in preweaning or arrival programs for less immunologically experienced calves.
T260 40701-40931 Sentence denotes There are no reliable peer-reviewed reports of field trials examining clinical effects of PI3 virus vaccines in North American beef cattle based on research that uses scientifically valid methods with clinically relevant outcomes.
T261 40932-41080 Sentence denotes 81 As a practical matter, it is difficult to select a multivirus BRD vaccine that does not include PI3 virus, making its inclusion less of an issue.
T262 41081-41224 Sentence denotes Findings reported in the literature are equivocal on the use of more recently available Pasteurella sp. vaccines before and on feedlot arrival.
T263 41225-41307 Sentence denotes The largest body of Pasteurella sp. vaccine data exists for P. haemolytica toxoid.
T264 41308-41610 Sentence denotes Three studies have shown statistically significant reduction in morbidity or mortality in calves administered a P. haemolytica toxoid on arrival?, 40, 66 Nevertheless, two clinical trials showed no significant effects when the same vaccine was given on arrival 69 or 3 weeks before shipment or arrival.
T265 41611-41690 Sentence denotes 107 Health performance in vaccinates was not affected negatively in any report.
T266 41691-41789 Sentence denotes There are individual reports on various other commercial or experimental Pasteurella sp. vaccines.
T267 41790-42169 Sentence denotes These include reports of significant efficacy in field studies of a streptomycin-dependent live Pasteurella sp. vaccine 52 and an intradermally administered live P. haemolytica vaccine. lOo Alternatively, a field study of a P. haemolytica capsular antigen vaccine failed to show significant health effects 44 as did a study using a tissue culture-derived P. haemolytica bacterin.
T268 42170-42436 Sentence denotes 35 For some currently available Pasteurella sp. vaccines, there are no reliable peer-reviewed reports of field trials examining clinical effects in North American beef cattle based on research that uses scientifically valid methods with clinically relevant outcomes.
T269 42437-42807 Sentence denotes There are reports of lack of field efficacy with earlier Pasteurella sp. bacterins.1, 75 There is also a report of increased health problems following vaccination with earlier Pasteurella sp. bacterins 9 ; however, this study did not mention whether treatment assignment was random, and the experimental unit is unclear, making the validity of the data analysis suspect.
T270 42808-42997 Sentence denotes Because of dose and timing requirements for optimal immunity (7-10 days following a 14-to 21-day booster dose) their value should be compromised when used only in a feedlot arrival program.
T271 42998-43084 Sentence denotes Paradoxically, the available data support the use of P. haemolytica toxoid on arrival.
T272 43085-43212 Sentence denotes The current consensus is that it is best to administer at least the priming dose and sometimes the booster dose before weaning.
T273 43213-43358 Sentence denotes As with other vaccine antigens for BRD prophylaxis, results of field trials evaluating the efficacy of H. somnus bacterins have been conflicting.
T274 43359-43695 Sentence denotes One group of investigators has reported negative effects of a single vaccination with a commercial H. somnus bacterin in that significantly more animals in groups of calves vaccinated once were treated for respiratory disease compared with groups of unvaccinated control calves or groups of calves vaccinated twice at a 21-day interval.
T275 43696-44364 Sentence denotes 74 These findings are in conflict with earlier reports by these authors that no significant difference in the number of animals treated was found between groups of calves immunized once with a commercial H. somnus bacterin and groups of nonimmunized control calves?5 Conversely, these investigators had reported earlier that morbidity (number of animals treated for respiratory disease) was significantly reduced in groups of calves vaccinated with a commercial H. somnus bacterin on arrival at the feedlot and revaccinated 21 days later compared with morbidity of groups vaccinated twice with a bivalent P. haemolytica, P. multocida bacterin or unvaccinated controls.
T276 44365-44518 Sentence denotes 1 The ability of H. somnus vaccine to reduce BRD in feedlots in the United States may be limited by the low incidence and sporadic nature of the disease.
T277 44519-44629 Sentence denotes 45 Although studies demonstrate vaccine efficacy, most have shown vaccine efficacy using septicemic challenge.
T278 44630-44697 Sentence denotes 103 Some have shown efficacy in experimental respiratory challenge.
T279 44698-44821 Sentence denotes 14 , 39 To date, however, efficacy has not been unequivocally demonstrated in well-controlled trials in a US field setting.
T280 44822-44946 Sentence denotes It is logical to assume that these vaccines are subject to the same dose and timing limitations as Pasteurella sp. vaccines.
T281 44947-44984 Sentence denotes There is no clear consensus on usage.
T282 44985-45134 Sentence denotes Field trials have been carried out with vaccinates receiving multiple antigens, making it impossible to determine the effects of individual antigens.
T283 45135-45304 Sentence denotes These can be subdivided into two broad groups: vaccine administered at or near the time of feedlot arrival and vaccine administered several weeks before feedlot arrival.
T284 45305-45413 Sentence denotes Assuming valid design, execution, and analysis, interpretation of the first group is fairly straightforward.
T285 45414-45524 Sentence denotes Some studies of arrival vaccination suggest that it does not affect or may even compromise health performance.
T286 45525-45661 Sentence denotes A well-designed study using IBR MLV and PI3 virus vaccine along with a P. haemolytica toxoid failed to show health performance benefits.
T287 45662-45978 Sentence denotes 6 This is supported by findings in a multiyear observational study in Ontario, Canada, which reported that administration of respiratory vaccines (IBR virus, IBR-PI3 virus, or IBR-PI3-Pasteurella sp. virus) to calves vaccinated within 2 weeks of arrival was associated with an increased risk of mortality (RR = 2.4).
T288 45979-46122 Sentence denotes 67 In contrast, subcutaneous vaccination with a P. haemolytica and H. somnus vaccine on arrival reduced BRD complex morbidity from 41 % to 29%.
T289 46123-46237 Sentence denotes 109 The second type of mixed antigen study is when vaccines are administered several weeks before feedlot arrival.
T290 46238-46300 Sentence denotes These are often part of a preconditioning or preweaning study.
T291 46301-46513 Sentence denotes Because an unvaccinated but similarly managed group is rarely included in these studies, the effects of management interventions such as preweaning and bunk acclimation are totally confounded with vaccine effect.
T292 46514-46613 Sentence denotes Hence, it is impossible to know which intervention accounts for improvements in health performance.
T293 46614-46781 Sentence denotes Vaccine injection only ensures that the animal has been exposed to the antigens contained in that vaccine; it does not ensure that a protective immune response ensues.
T294 46782-46899 Sentence denotes The two key components required for successful immunization are an efficacious vaccine and an immunocompetent animal.
T295 46900-47032 Sentence denotes Achieving a protective immune response to every pathogen in every animal in a population is probably impossible for several reasons.
T296 47033-47095 Sentence denotes Even if it were possible, it would likely be cost-prohibitive.
T297 47096-47227 Sentence denotes Based on their pathogenesis, some pathogens require each individual in a population to be immune for the vaccine to be efficacious.
T298 47228-47301 Sentence denotes One example is an infectious but noncommunicable disease such as tetanus.
T299 47302-47563 Sentence denotes For other pathogens, especially those that are highly contagious, reducing the number of susceptible animals below a critical threshold may be suffi-cient for the vaccine to be efficacious by preventing a disease outbreak, that is, the concept of herd immunity.
T300 47564-47725 Sentence denotes A vaccine may seem to be ineffective if it does not contain antigens that induce protective immunity to the disease-causing agent currently challenging the calf.
T301 47726-48021 Sentence denotes There are respiratory pathogens that can influence calf health for which no vaccines are available such as Chlamydia Sp.79 There are situations where antigenic differences between strains and species of pathogens or changes in antigens that the organism displays may compromise vaccine efficacy.
T302 48022-48096 Sentence denotes One example of this is the genetic and antigenic instability of BVD virus.
T303 48097-48246 Sentence denotes 20 This instability was thought to contribute to the failure of repeated annual doses of inactivated virus vaccine to protect animals from infection.
T304 48247-48345 Sentence denotes 56 For many infectious agents of cattle, immunologically important antigens are relatively stable.
T305 48346-48425 Sentence denotes A more likely cause of vaccine ineffectiveness is improper storage or handling.
T306 48426-48544 Sentence denotes We must store and administer vaccines according to the manufacturers' recommendations or risk reducing their efficacy.
T307 48545-48667 Sentence denotes Once we have done everything to properly care for the vaccine and the equipment, we must carefully administer the vaccine.
T308 48668-48818 Sentence denotes Training sessions should be conducted to ensure that personnel are knowledgeable about the proper locations and techniques for vaccine administration.
T309 48819-48894 Sentence denotes 47 Intramuscular injections should not be made behind the calf's front leg.
T310 48895-48972 Sentence denotes The subcutaneous route should be used whenever allowed by label instructions.
T311 48973-49073 Sentence denotes As a general rule, the smallest needle through which the product is easily delivered should be used.
T312 49074-49130 Sentence denotes For thin watery products, an IS-gauge needle works well.
T313 49131-49246 Sentence denotes Strict attention to proper restraint and changing needles to keep them sharp is critical if using IS-gauge needles.
T314 49247-49314 Sentence denotes Needle length should be adjusted for calf size and injection route.
T315 49315-49451 Sentence denotes Intramuscular injections should be given with a loS-in needle, except in the case of small calves in which a I-in needle should be used.
T316 49452-49523 Sentence denotes Subcutaneous injections should be made with a needle shorter than 1 in.
T317 49524-49593 Sentence denotes Needles should be changed whenever they become dull, barbed, or bent.
T318 49594-49690 Sentence denotes A clean needle should be used when refilling syringes to avoid contaminating the vaccine bottle.
T319 49691-49877 Sentence denotes Good handling facilities help minimize injection site reactions by ensuring that cattle are adequately restrained, thereby preventing movement should a calf struggle during an injection.
T1 49878-49997 Sentence denotes Sanitation is an important component of any vaccination plan and helps minimize injection site reactions and abscesses.
T2 49998-50100 Sentence denotes Contamination of a multidose container can result in vaccine inactivation and injection site problems.
T3 50101-50225 Sentence denotes Disinfectants inactivate MLV vaccines, so we must properly clean and rinse all equipment that comes in contact with vaccine.
T4 50226-50318 Sentence denotes Timing of vaccine administration can also influence our perception of vaccine effectiveness.
T5 50319-50490 Sentence denotes If an animal is incubating a disease or if it is exposed to the disease-causing agent soon following vaccination, it may get sick, and the vaccine seems to be ineffective.
T6 50491-50651 Sentence denotes It takes several days for an animal's immune system to respond to a vaccine and for the animal to be protected, especially if the calf is immunologically naive.
T7 50652-50763 Sentence denotes Experimentally, if we give enough of the disease-causing organism, we can cause disease even in immune animals.
T8 50764-50928 Sentence denotes When cattle are assem-bled in close quarters, the amount of disease agent to which they are exposed may be quite large, resulting in disease even in immune animals.
T9 50929-51132 Sentence denotes In summary, specific vaccine recommendations should be made by the veterinarian familiar with the management of the operation, including type of cattle handled and disease problems typically experienced.
T10 51133-51166 Sentence denotes There are few cookbook solutions.
T11 51167-51319 Sentence denotes Fine-tuning the program by including or excluding certain vaccines requires the identification of the specific disease entities present in an operation.
T12 51320-51419 Sentence denotes This requires good records, complete postmortem examinations, and a good diagnostic support system.
T13 51420-51584 Sentence denotes Effective management to optimize immunocompetence and timing of vaccine administration is as important as selecting the correct antigens and types of vaccines used.