Middle East respiratory syndrome coronavirus (MERS-CoV) is a zoonotic disease that was first identified in humans in 2012 in Saudi Arabia. MERS-CoV causes acute and severe respiratory disease in humans. The mortality rate of MERS in humans is ∼35% and >800 deaths have been reported globally as of August 2020. Dromedary camels are a natural host of the virus and the source of zoonotic human infection. In experimental studies, Bactrian camels are susceptible to MERS-CoV infection similar to dromedary camels; however, neither the virus, viral RNA, nor virus-specific antibodies were detected in Bactrian camel field samples so far. The aim of our study was to survey Mongolian camels for MERS-CoV-specific antibodies. A total of 180 camel sera, collected in 2016 and 2017, were involved in this survey: 17 of 180 sera were seropositive with an initial enzyme-linked immunosorbent assay (ELISA) test performed at the State Central Veterinary Laboratory in Mongolia. These 17 positive sera plus 53 additional negative sera were sent to the Rocky Mountain Laboratories, NIAID/NIH, and tested for the presence of antibodies with a similar ELISA, an indirect immunofluorescence assay (IFA), and a virus neutralization test (VNT). In these additional tests, a total of 21 of 70 sera were positive with ELISA and 10 sera were positive with IFA; however, none was positive in the VNT. Based on these results, we hypothesize that the ELISA/IFA-positive antibodies are (1) non-neutralizing antibodies or (2) directed against a MERS-CoV-like virus circulating in Bactrian camels in Mongolia.
Keywords: Bactrian camel; MERS-CoV; Mongolia; serology.