Scientists from the Netherlands and Qatar have produced the first definitive evidence that Middle East respiratory syndrome coronavirus (MERS-CoV) infects camels. The researchers used gene-sequencing techniques to show that three camels from a site where two humans contracted MERS-CoV were infected with the virus.
The research, published in The Lancet Infectious Diseases, suggests that the site – a small livestock barn in Qatar – was the location of an outbreak of MERS first detected in October 2013, when the barn’s owner, a 61-year-old man, was diagnosed with MERS-CoV infection, followed by a 23-year-old male employee of the barn.
Within a week of the barn’s owner being diagnosed with MERS, the Supreme Council of Health and Ministry of Environment in Qatar, in collaboration with the World Health Organisation (WHO), conducted a comprehensive investigation, collecting clinical samples (including nasal swabs, blood and rectal swabs, as well as stool samples) from 14 dromedary camels present at the barn. The samples were then sent to laboratories in the Netherlands for genetic analysis and antibody testing.
Comprehensive genetic analysis of the samples confirmed the presence of MERS-CoV in three camels. The virus sequences were very similar (although not identical) to those identified in the two humans at the site. All 14 of the camels tested had antibodies to MERS-CoV, suggesting that the virus might have been circulating among the animals for some time, allowing most of them to build up immune protection against infection.
According to the authors, “This is definitive proof that camels can be infected with MERS-CoV, but based on the current data, we cannot conclude whether the humans on the farm were infected by the camels or vice versa. A further possibility remains that humans and camels could have been infected from a third as yet unknown source. While additional sequencing may be giving slightly more resolution, there are other reasons why even that most likely will not give conclusive evidence. The big unknown is the exact timing of infections, both in the persons and in the camels.”
They add that, “A more detailed analysis of the outbreak, including testing of additional animals and environmental samples is ongoing, as well as attempts to obtain full MERS-CoV genomes of the human and animal specimens. We cannot rule out that other common livestock species including cattle, sheep and goats, or other animals including wildlife species are involved in the spread of MERS-CoV. In the meantime we recommend, based on the observations in this study, a detailed case history including review of any animal exposures including animal products, and targeted (prospective) serosurveys to determine what risk factors – other than contact with an infected person- are associated with human infection.”
Neil Ferguson and Maria Van Kerkhove, of Imperial College London, UK, write in a linked Comment that “An understanding of the role of animals in the transmission of MERS-CoV is urgently needed to inform control efforts. This virus can spread from person to person, sometimes causing substantial outbreaks, but whether the virus is capable of self-sustained (ie, epidemic) human-to-human transmission is unknown. If self-sustained transmission in people is not yet underway, intensive control and risk-reduction measures targeting affected animal species and their handlers might eliminate the virus from the human population. Conversely, if zoonotic exposure causes only a small fraction of human infections, then even intensive veterinary control efforts would have little effect on cases in people.”