Epistemic_Statements  

CORD-19:00adbbcc70c39794b7d91a479943c84cc33db30a JSONTXT 9 Projects

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Id Subject Object Predicate Lexical cue
T1 81-151 Epistemic_statement denotes The acquired immune system can be stimulated by effective vaccination.
T2 510-820 Epistemic_statement 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.
T3 1264-1361 Epistemic_statement denotes The complement system and phagocytic cells work more efficiently in a vaccinated animal, however.
T4 1508-1783 Epistemic_statement 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.
T5 1994-2151 Epistemic_statement 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.
T6 2152-2214 Epistemic_statement denotes Antibodies alone are not capable of killing infectious agents.
T7 2215-2290 Epistemic_statement denotes The presence of circulating IgG and IgM may help to control disease by: 1 .
T8 2706-2983 Epistemic_statement 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.
T9 4850-5111 Epistemic_statement 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.
T10 5112-5260 Epistemic_statement denotes Therefore, they can help to prevent invasion through the mucosal surface but are not very effective at controlling infection on the mucosal surface.
T11 5779-5900 Epistemic_statement denotes Secretory IgA is secreted onto mucosal surfaces, where it may bind to mucus and be present in fairly high concentrations.
T12 6412-6597 Epistemic_statement 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.
T13 6598-6713 Epistemic_statement denotes Despite these efforts, BRD is still a major problem, and its pathogenesis and etiology are incompletely understood.
T14 6877-7091 Epistemic_statement 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.
T15 7173-7283 Epistemic_statement denotes Under normal conditions, the bacteria are unable to move into the lower respiratory tract and cause pneumonia.
T16 7284-7433 Epistemic_statement denotes In fact, the lungs of normal healthy cattle can withstand a challenge with surprisingly large numbers of these bacteria without serious consequences.
T17 7434-7618 Epistemic_statement 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.
T18 7619-7933 Epistemic_statement 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.
T19 7934-8167 Epistemic_statement 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.
T20 8488-8644 Epistemic_statement 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.
T21 9261-9398 Epistemic_statement 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.
T22 9619-9767 Epistemic_statement 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.
T23 9768-9888 Epistemic_statement denotes The recrudescence of a latent BHVI infection in an animal under stress can lead to the spread of BHVI throughout a herd.
T24 10008-10123 Epistemic_statement denotes Even a modified live virus (MLV) vaccine strain can be recrudesced and shed under the influence of glucocorticoids.
T25 10290-10819 Epistemic_statement 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.
T26 10820-11084 Epistemic_statement 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.
T27 11085-11474 Epistemic_statement 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.
T28 11475-11726 Epistemic_statement 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.
T29 11727-11953 Epistemic_statement 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.
T30 11954-12130 Epistemic_statement 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.
T31 12131-12316 Epistemic_statement 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.
T32 12317-12596 Epistemic_statement 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.
T33 12597-12712 Epistemic_statement denotes Evidence suggests, however, that this is not as important as impairment of bactericidal mechanisms within the lung.
T34 13055-13261 Epistemic_statement 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.
T35 13584-13843 Epistemic_statement 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.
T36 14117-14200 Epistemic_statement denotes In addition to being bactericidal, these products also can damage pulmonary tissue.
T37 14201-14326 Epistemic_statement denotes If the infection is not brought under control relatively rapidly, the neutrophils can induce considerable damage in the lung.
T38 14327-14432 Epistemic_statement denotes There is evidence that BHVl, PI3 virus, BVD virus, and BRSV can each impair alveolar macrophage function.
T39 14433-14492 Epistemic_statement denotes 9o BHVl and BVD virus also can inhibit neutrophil function.
T40 14493-14589 Epistemic_statement denotes 90 The effects of PI3 virus and BRSV on neutrophil function apparently have not been determined.
T41 14853-15029 Epistemic_statement 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.
T42 15030-15321 Epistemic_statement 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.
T43 15569-15990 Epistemic_statement 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.
T44 15991-16082 Epistemic_statement denotes The clinical importance of immunosuppression by currently used MLV BVD vaccines is unknown.
T45 16083-16174 Epistemic_statement denotes It is probably not a problem when used in healthy animals under good management conditions.
T46 16310-16389 Epistemic_statement denotes The true prevalence of BIV infection of cattle in the United States is unknown.
T47 16462-16650 Epistemic_statement 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.
T48 16651-16814 Epistemic_statement 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.
T49 16815-16943 Epistemic_statement denotes The potential impact of naturally occurring infection with BIV on susceptibility to diseases in feedlot cattle is still unknown.
T50 16944-17126 Epistemic_statement denotes Several other viruses have been associated with the BRD complex, including bovine adenovirus, coronavirus, DN599 herpesvirus (Movar), rhinoviruses, reoviruses, and bovine parvovirus.
T51 17127-17338 Epistemic_statement 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.
T52 17339-17466 Epistemic_statement denotes Mycoplasma species (Mycoplasma hovis, Mycoplasma dispar, and ureaplasmas) also may be important factors in the etiology of BRD.
T53 17823-18111 Epistemic_statement 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
T54 18112-18207 Epistemic_statement denotes Nutrition plays an important role in maintaining optimal immune function and resistance to BRD.
T55 18264-18513 Epistemic_statement 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.
T56 18514-18694 Epistemic_statement 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.
T57 18695-18794 Epistemic_statement denotes Subclinical and clinical coccidiosis has also been shown to suppress neutrophil function in cattle.
T58 18795-18929 Epistemic_statement denotes 94 Substances secreted by nematodes progressing through larval stages have been shown to suppress proliferation of bovine lymphocytes.
T59 19297-19402 Epistemic_statement denotes Antibody titers as measured by a serum neutralization (SN) test can protect the animal against infection.
T60 19403-19554 Epistemic_statement denotes The evidence for this is that the passive antibodies that a calf receives from the colostrum can provide solid protection against infectious challenge.
T61 19555-19664 Epistemic_statement denotes The passively acquired antibody can also prevent an MLV vaccine from inducing an antibody response in a calf.
T62 19775-19958 Epistemic_statement 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.
T63 19959-20279 Epistemic_statement 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.
T64 20280-20505 Epistemic_statement 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.
T65 20506-20633 Epistemic_statement denotes This immunologic memory has been shown to provide partial protection against disease challenge with pseudorabies virus in pigS.
T66 20634-20770 Epistemic_statement 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.
T67 20996-21059 Epistemic_statement denotes Even MLV BHVl vaccine has been shown to latently infect cattle.
T68 21060-21130 Epistemic_statement denotes 3o The immune system is not capable of clearing this latent infection.
T69 21131-21314 Epistemic_statement 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.
T70 21315-21457 Epistemic_statement denotes 30, 93, 106 Therefore, serum neutralizing antibody can prevent infection, but it cannot prevent recrudescence and shedding of the latent BHVl.
T71 21458-21600 Epistemic_statement 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.
T72 21601-21742 Epistemic_statement denotes Once an infection with BHVl is established, a cell-mediated immune response is probably needed in order to bring the infection under control.
T73 21743-21824 Epistemic_statement denotes Cytotoxic T lymphocytes are thought to be important in controlling the infection.
T74 21825-21903 Epistemic_statement denotes There do not seem to be important antigenic differences between BHVl isolates.
T75 21904-22035 Epistemic_statement denotes Immunity to one isolate of BHVl or one vaccine strain of virus appears to provide good cross protection against all field isolates.
T76 22036-22167 Epistemic_statement denotes Therefore, an SN titer measured against any BHVl virus in the laboratory will more or less equally neutralize any other BHVl virus.
T77 22168-22385 Epistemic_statement 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.
T78 22386-22504 Epistemic_statement denotes SN antibody titers approximately greater than 1 to 32 have been shown to protect against disease induced by BVD virus.
T79 22505-22637 Epistemic_statement denotes ll A major problem, however, in immunity to BVD virus is that there is a great deal of antigenic diversity among BVD virus isolates.
T80 23039-23117 Epistemic_statement denotes This hypervariability may be due to selective pressure from the immune system.
T81 23118-23376 Epistemic_statement 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.
T82 23515-23739 Epistemic_statement 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.
T83 23740-23860 Epistemic_statement denotes In a field outbreak, it is impossible to predict which antigenic type of BVD virus the animal is going to be exposed to.
T84 23861-24101 Epistemic_statement 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.
T85 24102-24253 Epistemic_statement 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.
T86 24254-24336 Epistemic_statement denotes It is likely that cell-mediated immunity is important for recovery from infection.
T87 24337-24538 Epistemic_statement 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.
T88 24539-24658 Epistemic_statement denotes If this is true, an animal that has developed cell-mediated immunity has better protection against BVD virus challenge.
T89 24659-24841 Epistemic_statement 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.
T90 24842-25012 Epistemic_statement 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.
T91 25099-25197 Epistemic_statement denotes The type-2 BVD viruses have the potential to produce severe acute infection even in adult animals.
T92 25313-25492 Epistemic_statement 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.
T93 25493-25692 Epistemic_statement 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.
T94 25693-25854 Epistemic_statement 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.
T95 26234-26603 Epistemic_statement 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.
T96 26604-26775 Epistemic_statement 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.
T97 26940-27066 Epistemic_statement denotes Fetal protection experiments are expensive to perform but are needed to answer important questions regarding vaccine efficacy.
T98 27067-27156 Epistemic_statement denotes Circulating antibody does not seem to provide good immunity against BRSV-induced disease.
T99 27157-27392 Epistemic_statement 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.
T100 27393-27652 Epistemic_statement 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.
T101 27653-27958 Epistemic_statement 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.
T102 27959-28160 Epistemic_statement 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.
T103 28314-28514 Epistemic_statement 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.
T104 28515-28704 Epistemic_statement 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.
T105 28705-28995 Epistemic_statement denotes 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.
T106 29329-29487 Epistemic_statement denotes Protection against pneumonic lesions more closely correlated with antileukotoxin antibody responses than with lymphocyte gamma interferon production, however.
T107 29630-29737 Epistemic_statement denotes 34 P. haemolytica can be isolated in low numbers from the upper respiratory tract of normal healthy calves.
T108 29738-29911 Epistemic_statement 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.
T109 29912-30025 Epistemic_statement denotes These microcolonies then may successfully avoid the immune defenses in the alveolus and produce severe pneumonia.
T110 30026-30153 Epistemic_statement denotes Little is known about the ability of current vaccines to inhibit colonization of the upper respiratory tract by P. haemolytica.
T111 30154-30301 Epistemic_statement denotes Further research is needed to design and test vaccines that are capable of preventing or reducing upper respiratory colonization by P. haemolytica.
T112 30302-30391 Epistemic_statement denotes Not much is known about the nature of protective immunity to H. somnus-induced pneumonia.
T113 30392-30555 Epistemic_statement denotes H. somnus has a number of potential virulence factors that have been studied, including endotoxin, antibody binding proteins, surface nucleotides, and a hemolysin.
T114 30556-30762 Epistemic_statement 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.
T115 30763-31095 Epistemic_statement 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.
T116 31096-31265 Epistemic_statement 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.
T117 31373-31739 Epistemic_statement 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.
T118 31740-31897 Epistemic_statement 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.
T119 32258-32373 Epistemic_statement denotes Intramuscular MLV vaccines are thought to quickly induce immunity following proper administration of a single dose.
T120 32516-32646 Epistemic_statement denotes They may be used safely in calves suckling pregnant cows and can induce immunity in the face of residual maternal antibody titers.
T121 32647-32695 Epistemic_statement denotes They are, however, more difficult to administer.
T122 32805-32944 Epistemic_statement denotes Along with higher cost and concerns about shorter duration of immunity, this makes them less practical to use in a typical feedlot setting.
T123 32945-33067 Epistemic_statement denotes In a review of IBR virus vaccine clinical efficacy studies, results were positive or neutral; however, none were negative.
T124 33068-33187 Epistemic_statement denotes s1 The studies date to 1958 and 1974 and may not apply to current cattle feeding management practices in North America.
T125 34202-34245 Epistemic_statement denotes There is no clear consensus concerning use.
T126 34246-34494 Epistemic_statement 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.
T127 34495-34628 Epistemic_statement denotes 29 The use of MLV may be of greater concern in highly stressed cattle, but well-controlled studies evaluating this are not available.
T128 34629-34762 Epistemic_statement denotes As is the case with BHV1, dose and timing requirements of killed BVD virus vaccines are a severe limitation in most feedlot settings.
T129 35089-35276 Epistemic_statement 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.
T130 35488-35591 Epistemic_statement denotes 108 If this occurs during the first 6 months of pregnancy, fetal losses or immune tolerance may result.
T131 35718-35973 Epistemic_statement 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.
T132 35974-36281 Epistemic_statement 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
T133 36282-36411 Epistemic_statement denotes Critical studies comparing the ability of BVD MLV and killed vaccines to protect the fetus in field situations are not available.
T134 36412-36573 Epistemic_statement 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.
T135 36574-36744 Epistemic_statement denotes 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.
T136 36745-36871 Epistemic_statement denotes 10, 45, 53 The final injection should be at least 1 month before breeding in order to avoid detrimental effects on conception.
T137 36872-37037 Epistemic_statement 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.
T138 37038-37174 Epistemic_statement denotes The genetic and antigenic instability of BVD virus may result in the emergence of isolates that have reduced antigenic cross reactivity.
T139 37884-38011 Epistemic_statement denotes The opportunities for planned vaccination at noncritical stages of production and during times of minimal stress are available.
T140 38012-38116 Epistemic_statement denotes This makes infection from field strain viruses during critical periods of fetal development less likely.
T141 38117-38322 Epistemic_statement 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.
T142 38323-38485 Epistemic_statement 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.
T143 38550-38743 Epistemic_statement 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.
T144 38744-38880 Epistemic_statement denotes Nevertheless, it may still be possible for vaccination to attenuate clinical signs of subsequent infections and reduce time to recovery.
T145 38881-39197 Epistemic_statement 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.
T146 39198-39420 Epistemic_statement 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).
T147 39421-39536 Epistemic_statement denotes Freshly weaned and transported calves were 1.4 times less likely to be treated for BRD complex (OR = 1.4; P<O.OOl).
T148 39656-39999 Epistemic_statement 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.
T149 40222-40357 Epistemic_statement denotes Although there is evidence to support BRSV vaccine usage in naive or mismanaged calves, inclusion in vaccine regimens is not universal.
T150 40444-40593 Epistemic_statement 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.
T151 40594-40700 Epistemic_statement denotes Vaccination may be valuable in preweaning or arrival programs for less immunologically experienced calves.
T152 40932-41080 Epistemic_statement 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.
T153 42629-42807 Epistemic_statement denotes 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.
T154 42808-42997 Epistemic_statement 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.
T155 42998-43084 Epistemic_statement denotes Paradoxically, the available data support the use of P. haemolytica toxoid on arrival.
T156 43213-43358 Epistemic_statement denotes As with other vaccine antigens for BRD prophylaxis, results of field trials evaluating the efficacy of H. somnus bacterins have been conflicting.
T157 44365-44518 Epistemic_statement 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.
T158 44519-44629 Epistemic_statement denotes 45 Although studies demonstrate vaccine efficacy, most have shown vaccine efficacy using septicemic challenge.
T159 44698-44821 Epistemic_statement denotes 14 , 39 To date, however, efficacy has not been unequivocally demonstrated in well-controlled trials in a US field setting.
T160 44822-44936 Epistemic_statement denotes It is logical to assume that these vaccines are subject to the same dose and timing limitations as Pasteurella sp.
T161 44947-44984 Epistemic_statement denotes There is no clear consensus on usage.
T162 45135-45304 Epistemic_statement 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.
T163 45414-45524 Epistemic_statement denotes Some studies of arrival vaccination suggest that it does not affect or may even compromise health performance.
T164 45862-45978 Epistemic_statement denotes virus) to calves vaccinated within 2 weeks of arrival was associated with an increased risk of mortality (RR = 2.4).
T165 46301-46513 Epistemic_statement 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.
T166 46514-46613 Epistemic_statement denotes Hence, it is impossible to know which intervention accounts for improvements in health performance.
T167 46900-47032 Epistemic_statement denotes Achieving a protective immune response to every pathogen in every animal in a population is probably impossible for several reasons.
T168 47033-47095 Epistemic_statement denotes Even if it were possible, it would likely be cost-prohibitive.
T169 47302-47563 Epistemic_statement 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.
T170 47564-47725 Epistemic_statement 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.
T171 47726-48021 Epistemic_statement 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.
T172 48097-48246 Epistemic_statement denotes 20 This instability was thought to contribute to the failure of repeated annual doses of inactivated virus vaccine to protect animals from infection.
T173 48346-48425 Epistemic_statement denotes A more likely cause of vaccine ineffectiveness is improper storage or handling.
T174 48426-48544 Epistemic_statement denotes We must store and administer vaccines according to the manufacturers' recommendations or risk reducing their efficacy.
T175 48545-48667 Epistemic_statement denotes Once we have done everything to properly care for the vaccine and the equipment, we must carefully administer the vaccine.
T176 48668-48818 Epistemic_statement denotes Training sessions should be conducted to ensure that personnel are knowledgeable about the proper locations and techniques for vaccine administration.
T177 48819-48894 Epistemic_statement denotes 47 Intramuscular injections should not be made behind the calf's front leg.
T178 48895-48972 Epistemic_statement denotes The subcutaneous route should be used whenever allowed by label instructions.
T179 48973-49073 Epistemic_statement denotes As a general rule, the smallest needle through which the product is easily delivered should be used.
T180 49131-49246 Epistemic_statement denotes Strict attention to proper restraint and changing needles to keep them sharp is critical if using IS-gauge needles.
T181 49247-49314 Epistemic_statement denotes Needle length should be adjusted for calf size and injection route.
T182 49315-49451 Epistemic_statement 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.
T183 49452-49523 Epistemic_statement denotes Subcutaneous injections should be made with a needle shorter than 1 in.
T184 49524-49593 Epistemic_statement denotes Needles should be changed whenever they become dull, barbed, or bent.
T185 49594-49690 Epistemic_statement denotes A clean needle should be used when refilling syringes to avoid contaminating the vaccine bottle.
T186 49691-49877 Epistemic_statement 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.
T187 49998-50100 Epistemic_statement denotes Contamination of a multidose container can result in vaccine inactivation and injection site problems.
T188 50101-50225 Epistemic_statement denotes Disinfectants inactivate MLV vaccines, so we must properly clean and rinse all equipment that comes in contact with vaccine.
T189 50226-50318 Epistemic_statement denotes Timing of vaccine administration can also influence our perception of vaccine effectiveness.
T190 50319-50490 Epistemic_statement 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.
T191 50652-50763 Epistemic_statement denotes Experimentally, if we give enough of the disease-causing organism, we can cause disease even in immune animals.
T192 50764-50928 Epistemic_statement 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.
T193 50929-51132 Epistemic_statement 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.