Antibodies against MERS Coronavirus in Dromedary Camels, United Arab Emirates, 2003 and 2013

Abstract

Middle East respiratory syndrome coronavirus (MERS-CoV) has caused an ongoing outbreak of severe acute respiratory tract infection in humans in the Arabian Peninsula since 2012.Dromedaries have been implicated as possible viral reservoirs.We used serologic assays to analyze 651 dromedary serum samples from the United Arab Emirates; 151 of 651 samples were obtained in 2003, well before onset of the current epidemic, and 500 serum samples were obtained in 2013.Recombinant spike protein-specific immunofluorescence and virus neutralization tests enabled clear discrimination between MERS-CoV and bovine CoV infections.Most (632/651, 97.1%) dromedaries had antibodies against MERS-CoV.This result included all 151 serum samples obtained in 2003.Most (389/651, 59.8%) serum samples had MERS-CoV-neutralizing antibody titers >1,280.Dromedaries from the United Arab Emirates were infected at high rates with MERS-CoV or a closely related, probably conspecific, virus long before the first human MERS cases. M iddle East respiratory syndrome coronavirus (MERS-CoV) is an emerging pathogen associated with severe respiratory symptoms and renal failure in infected patients (1,2).Globally, 156 laboratory-confirmed cases of infection with MERS-CoV, including 65 deaths, were reported as of early November 2013.All human cases were linked to the Arabian Peninsula (Saudi Arabia, Jordan, Oman, Qatar, Kuwait, and the United Arab Emirates).Imported cases were detected in countries in Europe and Africa (United Kingdom, Germany, Italy, France, and Tunisia) (3).Transmission patterns, including the putative zoonotic source of the virus, remain unclear.Hypotheses include frequent zoonotic infections with limited subsequent human-to-human transmission chains and existence of a self-sustained epidemic in humans (4).A recent study found evidence to support the existence of epidemiologically unlinked cases in a large outbreak in the al-Hasa region, Saudi Arabia (5).It was speculated that zoonotic introductions of MERS-CoV from an unknown reservoir might occur at high rates, in addition to obvious human-tohuman transmission.Coronaviruses (CoV) are positive-sense RNA viruses.Viruses in the genera Alphacoronavirus and Betacoronavirus are associated with mammals and show a particularly high level of diversification in bats.Viruses in the genera Gammacoronavirus and Deltacoronavirus are mostly avian-associated viruses (6,7).MERS-CoV belongs to Betacoronavirus phylogenetic lineage C that, in addition to MERS-CoV, contains 2 distinct bat-associated CoV species (HKU4 and HKU5) (1,8).Insectivorous bats of the family Vespertilionidae were recently shown to carry viruses that are probably conspecific with MERS-CoV (9).However, the limited rate of contact between humans and insectivorous bats makes a continuous and frequent acquisition of MERS-CoV from bats an unlikely scenario.In a manner similar to observations regarding severe acute respiratory syndrome CoV (SARS-CoV), an intermediate reservoir host might exist from which human infections are acquired.Dromedaries from Antibodies against MERS Coronavirus in Dromedaries, United Arab Emirates, 2003 and 2013