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While the rate of new MERS-CoV infections being reported on the Arabian peninsula has dropped in the past couple of months, scientific interest in the source, epidemiology, and evolution of the virus has not. Today, the open access journal mBio carries a major study that appears to answer one of the big questions regarding this emerging disease, pegging dromedary camels as (at least one of) the virus’s reservoir hosts.
Overnight Crof carried a report by NPR’s Richard Knox (see Deadly MERS Virus Circulates Among Arabian Camels) which – in addition to characterizing this study – provides a fascinating look at the often contentious nature of recent MERS research collaborations in Saudi Arabia. Highly recommended.
As you’ll probably recall, while the source of the MERS coronavirus has remained elusive, both bats and camels have been considered prime suspects, with serological tests over the past year pointing in both species’ direction. Given the past association of coronaviruses with bats, they were among the first suspects, but as recently as last month the OIE had this to say about their role.
Although a relative to this virus had already been detected in bat species, and a fragment of viral genetic material matching the MERS CoV was recently found in one bat from Saudi Arabia, more evidence is needed to directly link the MERS CoV to bats or other animal species.
Last August, the first serological evidence was presented (see Lancet: Camels Found With Antibodies To MERS-CoV-Like Virus) that dromedaries (single-humped camels) carried a MERS-Like virus, although the virus was not isolated or matched 100% to the MERS coronavirus.
In late November, additional support for the camel connection came when Qatari officials announced that the MERS virus had been detected in Camels on a farm where two people had become infected (see Qatar Supreme Council of Health Statement On MERS-CoV In Camels), and that further investigations were underway by the local Health Ministry and RIVM laboratory and Erasmus Medical Centre in the Netherlands.
In December, The Lancet published a study (see Identification Of MERS Virus In Camels), led by Marion Koopmans, DVM, PhD, head of virology at the Laboratory for Infectious Diseases at the RIVM in the Netherlands, that determined that the human viruses and the camel viruses from the Qatari farm were almost an identical match.
So close, in fact, that they were unable to determine whether the humans or the camels were infected first.
While not eliminating bats from the equation (or even possibly, other animal hosts), today we have the most compelling study to date showing that camels have been a long-standing reservoir for the MERS coronavirus in Saudi Arabia.
First some excerpts from the American Society for Microbiology press release, followed by the link to the study, after which I’ll be back with a bit more.
Coronavirus has been infecting the animals for at least 20 years
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 to be published on February 25 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."
Lead authors for the paper were Abdulaziz Alagaili of King Saud University and the Saudi Wildlife Authority in Riyadh and Thomas Briese of Columbia University.
The link, and abstract to the open access study follow:
Abdulaziz N. Alagailia,b, Thomas Briesec, Nischay Mishrac, Vishal Kapoorc, Stephen C. Sameroffc, Emmie de Witd, Vincent J. Munsterd, Lisa E. Hensleye, Iyad S. Zalmouta, Amit Kapoorc, Jonathan H. Epsteinf, William B. Kareshf, Peter Daszakf, Osama B. Mohammeda, W. Ian Lipkinc
The Middle East respiratory syndrome (MERS) is proposed to be a zoonotic disease; however, the reservoir and mechanism for transmission of the causative agent, the MERS coronavirus, are unknown. Dromedary camels have been implicated through reports that some victims have been exposed to camels, camels in areas where the disease has emerged have antibodies to the virus, and viral sequences have been recovered from camels in association with outbreaks of the disease among humans. Nonetheless, whether camels mediate transmission to humans is unresolved. Here we provide evidence from a geographic and temporal survey of camels in the Kingdom of Saudi Arabia that MERS coronaviruses have been circulating in camels since at least 1992, are distributed countrywide, and can be phylogenetically classified into clades that correlate with outbreaks of the disease among humans. We found no evidence of infection in domestic sheep or domestic goats.
IMPORTANCE This study was undertaken to determine the historical and current prevalence of Middle East respiratory syndrome (MERS) coronavirus infection in dromedary camels and other livestock in the Kingdom of Saudi Arabia, where the index case and the majority of cases of MERS have been reported.
Today’s study seems to nail down that MERS-CoV is a common, likely mild or asymptomatic, infection in young camels in Saudi Arabia and suggests that they may well be the source of at least some portion of the human infections we’ve seen over the past two years.
Still, the majority of human cases have reported no recent camel exposure, leaving a large and disconcerting gap in the epidemiology of the disease.
It has been speculated that other animal species may harbor and transmit the virus, but that has yet to be proven. Nor has fomite (contaminated inanimate objects) transmission, even though last September in Eurosurveillance: Environmental Stability Of MERS-CoV) we saw remarkable evidence of the viability of the virus on surfaces, and in the air.
Another possibility, that the virus is circulating stealthily at low levels among the human population – often only causing mild or asymptomatic disease – can’t be ignored either.
Despite the insistence of the Saudi Ministry of Health to the contrary, many researchers feel the kind of in-depth epidemiological investigations needed to answer these – and other - vital questions have not been done.
One that will hopefully provide badly needed answers before the MERS virus decides to stage a major comeback.