The coronavirus responsible for Middle East Respiratory Syndrome (MERS) is prevalent in camels throughout Saudi Arabia and has been around for at least 20 years, according to a study published in mBio®, the online open-access journal of the American Society for Microbiology.
"Our study shows the MERS coronavirus (MERS-CoV) is widespread," says senior study author W. Ian Lipkin of Columbia University, New York. "Adult camels were more likely to have antibodies to the virus while juveniles were more likely to have active virus. This indicates that infection in camels typically occurs in early life, and that if people get the virus from camels the most likely source is young camels."
MERS, a serious viral respiratory illness, has been identified in 182 people from 2012 through Feb. 7, according to the World Health Organization; 79 people have died from the condition. While most infections have occurred in Saudi Arabia, the origin of disease, in most cases, has remained unknown. Efforts to identify an animal source of infection have focused on bats and camels. The first known case of MERS was in a Saudi Arabian man who had four pet camels.
In the study, investigators from the United States and Saudi Arabia conducted a comprehensive survey of dromedary camels throughout Saudi Arabia. They collected blood samples and rectal and nasal swabs from camels, sheep and goats in November and December of 2013. Using mobile laboratory equipment, they tested blood samples for antibodies reactive with MERS-CoV, and the swabs and blood for active virus. They also analyzed archived blood samples from dromedary camels taken from 1992 through 2010.
Overall, 74% of camels sampled countrywide had antibodies to MERS-CoV. More than 80% of adult camels throughout the country had antibodies to the virus, while in camels age two or younger the prevalence ranged from 90% in the east to 5% in the southwest. Antibodies to the virus were seen in camel serum samples dating back to 1992, which strongly suggests that either MERS-CoV or a closely related virus has been circulating in the Saudi Arabian animals for at least two decades.
The researchers also found that active virus was frequently detected in nasal swabs in 35% of young camels and 15% of adult camels countrywide. It was less frequently found in rectal swabs and not in blood, indicating that the virus most likely is spread by respiratory secretions.
While they speculate that camels are potential reservoirs for human transmission, the authors say the current study does not prove that. "Our findings suggest that continuous, longer-term surveillance will be necessary to determine the dynamics of virus circulation in dromedary camel populations."