MERS-coronavirus: From discovery to intervention

Widagdo, W.; Okba, Nisreen M.A.; Stalin Raj, V.; Haagmans, Bart L.

The zoonotic capacity of MERS-CoV was suggested already at the beginning of its emergence, since it was observed that the virus is closely related to bat CoVs but not to other human CoVs [3, 8] . Bats have been suggested to be one of the natural hosts of MERS-CoV but the evidence supporting transmission of this virus from bats to other species is currently lacking. Serology-based assays applied using sera from various animal species in search of the animal hosts for MERS-CoV, revealed the dromedary camel as the most likely zoonotic source for MERS-CoV [13, 66, 67] . The high percentage of seropositivity against MERS-CoV among camels in the Arabian Peninsula and Africa, as early as the 1980s, indicates that MERS-CoV did circulate in this animal long before being introduced to the human population [13, 14, [66] [67] [68] [69] [70] [71] [72] . Screening of dromedary camel nasal swabs subsequently led to identification and isolation of MERS-CoV from dromedaries, confirming its circulation in this animal species [14, 47, 73, 74] . Camels develop mild upper respiratory tract infections upon experimental inoculation of MERS-CoV, consistent with localization of DPP4 at this location [43, 75, 76] . Furthermore, two studies of human MERS cases post-contact with infected camels reported high similarity in virus sequences obtained from both the camels and humans [47, 77] . These studies along with a case control study identifying direct exposure to camels as a risk factor for MERS-CoV infection, and serology studies showing higher seropositivity among camel contacts compared to non-camel contacts, support camel-to-human transmission of MERS-CoV [15, 17, 46] . The risk of humans acquiring MERS-CoV infection from camels could be high due to the wide geographical distribution of MERS-CoV seropositive camels, also demonstrated by the fact that MERS-CoV seropositive livestock handlers were identified in Kenya [78] , but it might be underestimated due to unrecorded subclinical infections in humans.