Pathogenesis and Transmissibility of Middle East Respiratory Syndrome Coronaviruses of African Origin in Alpacas

The Middle East respiratory syndrome coronavirus (MERS-CoV) remains a highly significant threat to global public health. Dromedary camels are the zoonotic source of human infection. All cases of zoonotic Middle East respiratory syndrome (MERS) have occurred in Middle Eastern countries despite MERS-CoV infection of camels being widespread in Africa. This disparity in the geographic burden of the disease may be due to genomic differences between MERS-CoV circulating in Middle Eastern countries (clades A and B) versus those infecting camels in Africa (clade C), although the precise genetic determinants of virulence remain to be elucidated. The objective of the studies reported here was to evaluate differences in the magnitude of virus shedding and in transmissibility of clades A/B and C viruses using alpacas as a surrogate for dromedary camels. We found that two of three African-origin, clade C strains of MERS-CoV induced very reduced levels of virus shedding and were transmitted inefficiently to contact control animals as compared to one other clade C virus and representative viruses from clade A and B. Lower virus titers in the nasopharynx may be associated with lower zoonotic transmission and human disease severity and may explain the observed epidemiology of MERS-CoV in Africa where zoonotic disease appears rare. These results add to our understanding of the transmission of different lineages of MERS CoV in camelids and zoonotic transmission.