Zoonotic threat from MERS coronavirus

Abstract

Coronaviruses (CoV) are RNA viruses with capacity for generating genetic diversity by mutation and recombination. Human coronaviruses 229E, OC43, HKU1 and NL63, are known to be endemic in humans. Of these, 229E, OC43 and NL63 have crossed to from animals to humans within the past few hundred years; 229E from bats via camels to humans, OC43 from cattle and NL63 from bats. The precursor of SARS coronavirus is present in bats, emerged from game animal markets in Guangdong province, China, and led to an outbreak that spread globally to infect almost 8000 people in 25 countries. MERS-CoV is the most recent coronavirus of zoonotic and potential epidemic concern. It is endemic in dromedary (but not Bactrian) camels in the Arabian Peninsula as well as Africa and Central Asia. The virus is more commonly detected in camel calves but can re-infect previously sero-positive animals and can be detected at high prevalence in camel markets and abattoirs where animals from many sources are mixed together. Zoonotic infections have only been reported from the Arabian Peninsula and the reason for an apparent lack of zoonotic MERS in Africa remains to be elucidated. Viral genetic and phenotypic analysis of MERS-CoV from Africa provides some possible explanations. Zoonotic transmission events are often mild and unrecognized and become apparent when older persons with co-morbidities are involved. Zoonotic events can lead to transmission in humans within health care facilities, leading to large disease outbreaks. Late recognition and diagnosis and health care workers continuing to work with mild illness contribute to nosocomial outbreak. Molecular epidemiology can help elucidate transmission patterns within hospitals. It is possible that the greater stability of the virus in air-conditioned environments contributes to such outbreaks. Sero-epidemiological studies indicate that reported cases significantly under-estimate the true extent of infections taking place.