MERS-CoV in sheep, goats, and cattle, United Arab Emirates, 2019:
Virological and serological investigations reveal an accidental
spillover from dromedaries
Abstract
The recent COVID-19 pandemic has demonstrated again the global threat
posed by emerging zoonotic coronaviruses. During the past two decades
alone, humans have experienced the emergence of several coronaviruses,
such as SARS-CoV in 2003, MERS-CoV in 2012, and SARS-CoV-2 in 2019. To
date, MERS-CoV has been detected in 27 countries, with a case fatality
ratio of approximately 34.5 %. Similar to other coronaviruses, MERS-CoV
presumably originated from bats; however, the main reservoir and primary
source of human infections are dromedary camels. Other species within
the Camelidae family, such as Bactrian camels, alpacas, and
llamas, seem to be susceptible to the infection as well, although to a
lesser extent. In contrast, susceptibility studies on sheep, goats,
cattle, pigs, chickens, and horses obtained divergent results. In the
present study, we tested nasal swabs and/or sera from 55 sheep, 45
goats, and 52 cattle, collected at the largest livestock market in the
United Arab Emirates, where dromedaries are also traded, for the
presence of MERS-CoV nucleic acid by RT-qPCR, and for specific
antibodies by immunofluorescence assay (IFA). All sera were negative for
MERS-CoV-reactive antibodies, but the nasal swab of one sheep (1.8 %)
was positive for MERS-CoV nucleic acid. Next generation sequencing (NGS)
of the complete N gene of the sheep-derived MERS-CoV revealed
>99 % nucleotide identity to MERS-CoV sequences of five
dromedaries in nearby pens and to three reference sequences. The NGS
sequence of the sheep-derived MERS-CoV was confirmed by conventional
RT-PCR of a part of the N gene and subsequent Sanger sequencing.
All MERS-CoV sequences clustered within clade B, lineage 5. In
conclusion, our study shows that non-camelid livestock, such as sheep,
goats, and cattle do not play a major role in MERS-CoV epidemiology. The
one sheep that tested positive most likely reflects an accidental viral
spillover event from infected dromedaries in nearby pens.