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To appear in: One Health
Abstract
. The WHO have announced that the disease caused by the SARS-CoV-2 is referred to as coronavirus disease-2019 (COVID-19) [15] .
Despite recent efforts in basic and translational influenza and coronavirus research, there is still no vaccine against coronaviruses for use in humans (this includes SARS and MERS) [16] [17] [18] [19] . In addition, there is yet no universal influenza vaccine available against all influenza virus subtypes and hence seasonal influenza vaccines have to be updated annually and that vaccines for pandemic preparedness are a challenge [20] [21] [22] [23] [24] [25] . The lack of preventive vaccines for clinical use in humans against such viruses makes emerging influenza and coronaviruses a serious global threat.
Since the emergence of SARS-CoV and MERS-CoV, bats have been the suspect of harbouring emerging viruses. Several studies have recently reported the detection of coronaviruses of pandemic potential [26, 27] . Genetic evolutionary analysis of SARS-CoV-2 revealed that this virus is genetically related to two bat coronaviruses [7, 28] . Contrary to SARS-CoV and MERS-CoV, SARS-CoV-2 cases have been reported to a quite large extent outside the epicentre of the infection. The numbers of infections due to SARS-CoV-2 continued to grow since its emergence till January 31 (figure 1), and as of the date of this publication, the virus has caused more than 74,000 confirmed and reported infections in humans globally [11, 29] . Through rapid and frequent international air travel, infections due to SARS-CoV-2 have spread to over 26 countries around the world causing more than 2,000 deaths including four deaths outside China in the Japan, Taiwan, the Philippines and France have been reported as of 19 February, 2020 [9, 29] .
The epidemiological data available at the time of this publication are summarized in figure 2 [10] . Infections due to SARS-CoV-2 are yet unreported at the time of this publication in South American countries. Except for Egypt where one travel-related case was reported on 12 February The case fatality rate is calculated by dividing the number of known deaths by the number of confirmed cases. The resulting number, however, does not represent the true case fatality rate and might be off by orders of magnitude [30] . The true case fatality rate is unknown at this stage of the outbreak, and its precise estimate is impossible at present [30, 31] . Globally, the clinical picture in humans infected with SARS-CoV-2 have ranged from mild (no or few signs and symptoms), to severe, including death. It was reported that the first instance of COVID-19 related pneumonia cases, whether linked to the Huanan Seafood market or not, occurred between 6 and 15 December 2019 [33] . Another study reported the onset of pneumonia cases related to COVID-19 occurred between the 1 st and 10 th of December [8] . It is unclear whether the COVID-19 pneumonia related cases had occurred undetected in Wuhan, China prior to the 1 st December 2019, this requires further investigation.
Retrospective serological investigation of pneumonia cases in Wuhan before December 2019 will determine the extent of early unreported cases. It will also help determine whether SARS-CoV-2 circulated in Wuhan before December 2019 and will help track the origin of this outbreak among Chinese populations and humans in other parts of the world who had travel history to the epicentre prior to the known start of the outbreak. It was previously reported that the sensitive and specific serological detection of MERS-CoV in subclinical infection is challenging [34, 35] .
SARS-CoV-2 can cause asymptomatic to fatal respiratory diseases [36] . Asymptomatic to mild COVID-19 infections can go unnoticed and there may be a lack of seroconversion among nucleic acid PCR-confirmed cases which requires further serosurveillance studies. Evaluation of the serologic response of SARS-CoV-2 infected patients according to the disease severity will help determine the potential role of serodiagnostic parameters as prognostic markers. The development of accurate and robust serological assay will help determine the accurate SARS-CoV-2 prevalence.
Infections due to SARS-CoV-2 among healthcare workers and family clusters were also reported and human-to-human transmission has been confirmed [37] , however further investigations are required to determine and understand the full extent of this mode of transmission. So far, there is no evidence of airborne transmission of the SARS-CoV-2, however precautionary measures are recommended due to the lack of information excluding this mode of transmission. The present COVID-19 outbreak is the third global alert of coronavirus infections. SARS-CoV-2
transmission in humans appears efficient and the virus is of pandemic potential. As of today, public health measures in China are yet unable to halt the spread of human infections. There is great concern that spread of the virus may be devastating and of huge public health concern globally, especially in resource-limited countries Based on the general definition of a pandemic as an infection that spreads globally, COVID-19 is already a "pandemic". On January 30, 2020, the International Health Regulations Emergency Committee of the World Health Organization declared COVID-19 outbreak a public health emergency of international concern (PHEIC) [38] . Subsequently, the US declared it a public health emergency on January 31, 2020 [39] , and several travel restrictions to the epicentre of the outbreak were imposed by the USA, Canada, UK, many countries in Europe, the Philippines, several other countries have followed similar travel restriction [40, 41] to avoid SARS-CoV-2 infection importation by air travel.
COVID-19 is a recent example of the complex threats of emerging infectious diseases. Emerging infections in humans and animals, along with other threats such as antimicrobial resistance, are difficult challenges to humanity, to a large extent driven by increasing food production and other issues related to a growing and more resource-demanding population. The interdisciplinary One
Health approach represents an attempt to deal with such complex problems engaging J o u r n a l P r e -p r o o f professionals from many disciplines such as human, veterinary, and environmental health, as well as social sciences [42] . The One Health approach recognizes the interrelationship between animals, humans and the environment and encourages collaborative efforts to improve the health of people and animals, including pets, livestock, and wildlife [43] . One Health teams can work to identify sources of emerging pathogens and ways to reduce the threat of outbreaks [44] . The implementation and development of One Health collaborations on a global scale are critical to reduce the threats of emerging viruses [42, 43] .
Regarding SARS-CoV-2 in particular, there are several aspects that needs a One Health approach in order to understand the outbreak, and to mitigate further outbreaks of a similar virus. SARS-CoV-2 is likely a bat-origin coronavirus that was transmitted to humans through a spill over from bats or through an undetermined yet intermediate animal host (avian, swine, phocine, bovine, canine, other species) or wild animals. Figure 3 depicts a transmission hypothesis of SARS-CoV-2 outbreak, yet the intermediate host is to be determined. The list of animals which were sold range between poultry (turkey, pheasants, geese, roosters, doves, and wild birds (Peacocks swans, and exotic animals, to reptiles and hedgehogs. The animal list included frogs, camels, wild rabbits, reptiles, snakes, deer, crocodiles, Kangaroos, snails, civet cats, goats, centipedes, and cicades [45, 46] . There are no data available in scientific literature on the detection and isolation of SARS-CoV-2 from environmental samples. However, it was recently reported that the Chinese Centers for Disease Control and Prevention isolated SARS-CoV-2 from 33 samples out of 585 environmental samples collected from Huanan Seafood Market [47] . process, and they need to be addressed in any true One Health approach [48] . However, it is crucial to consider the cultural context of these markets meaning that again, social sciences are important in this process. Also, this means that the most viable solution may not be to close down live animal markets but perhaps to 'sector' them so that fewer different species mingle in one specific market and that the specific intermediate host(s) for SARS-CoV-2 may be removed from the markets, or rigorously tested for the virus.
iii) Decreasing the human-to-human transmission. This is obviously a crucial measure to stop the current outbreak, and rightfully attracts the most attention at the present time. This review does not aspire to cover the large subject of human-to-human transmission control, but also here a mixture of measures is important from strictly medical (transmission routes, efficiency of PPE, vaccines, antivirals and so on) to more social science-oriented (How do people behave when they suspect they could be infected? How do they behave when they are sick? How to potentially change these behaviours?).
To successfully decrease the risk for a new SARS-CoV-2 outbreak or an outbreak of a similar virus, a One Health approach is crucial.
In conclusion, SARS-CoV-2 which causes COVID-19 is continuing to cause global fears, psychological distress, economic losses and negative impacts on several human activities including industry and mobility. To date, SARS-CoV-2 does not represent a pandemic threat with the same severity as e.g. the 1918 Spanish influenza, but could still cause a high number of J o u r n a l P r e -p r o o f deaths and put enormous strain on healthcare systems if widespread globally. Likely, resourcelimited countries will be hit hardest due to smaller healthcare budgets and less possibilities of diagnostics and infection control.
There is an urgent need for the implementation of multidisciplinary One Health to address the current complex health challenges at the human-animal-environment interface [42, 43] One Health approaches in China have recently been described [49] [50] [51] [52] . However, the implementation of One Health policies in China is challenged by several barriers [48, 51] .
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