Searching for animal models and potential target species for emerging pathogens: Experience gained from Middle East respiratory syndrome (MERS) coronavirus

Vergara-Alert, Júlia; Vidal, Enric; Bensaid, Albert; Segalés, Joaquim

As summarized in this review, several species of animals are susceptible to experimental MERS-CoV infection; thus, they might act as potential intermediate hosts of the disease. However, the presence of viral RNA and/or specific antibodies against the virus has been only demonstrated in the field in dromedaries and alpacas [41, 51] . At the light of recent experimental studies, it seems that the list of potential host targets for MERS-CoV is not closed. MERS surveillance programs should be implemented in endemic areas in animal species for which experimental evidence of susceptibility has been provided and species closely related to them. SARS and MERS outbreaks taught us many lessons, and one of the most important is that, even in the absence of an overt threat, there is the possibility of the re-emergence of a virus or other similar viruses. On the other hand, and since the first case of MERS, continuous new cases have been described in different countries around the world [59] [60] [61] [62] . This underlines the importance of the development of animal models closer to the natural host targets. The key role of domestic animals and wildlife in the transmission of MERS-CoV should be further elucidated; meanwhile, countermeasures against deadly coronaviruses must be further explored since the risk of a global outbreak is not negligible. Noteworthy, after more than a decade of SARS and five years of MERS epidemics, there are still no licensed preventive or therapeutic drugs available that could be used in case of an eventual re-emergence of SARS or MERS. This scenario is not the outcome of technical issues, since effective vaccine prototypes against those pathogens are already available [53, 63, 64] . In case of MERS-CoV, vaccination of dromedary camels, the main source of zoonotic transmission, might be useful to control the spread of MERS [53] . However, when developing a vaccine, besides testing the protection efficacy, researchers need to think about social problems such as the reticence of camel owners to vaccinate their animals. Thus, the development of a dual vaccine able to protect against both, MERS-CoV and camelpox virus (an endemic disease in the Middle East, Africa and Asia) might be an ideal solution [53] . Recently, another dual-vaccine for humans and animals against MERS-CoV and rabies virus has been designed [65] . Political aspects have also a key role in the release of a vaccine into the market. Unless the requirements and timings for vaccine licensing procedures are facilitated, pharmaceutical companies will unlikely invest in their development taking into account the current market demand. Moreover, fragmentation of intellectual property rights may also adversely affect the development of vaccines to combat those infections [66] .