A case report on a camel-to-human transmission of Middle East respiratory syndrome coronavirus (MERS-CoV) offers the first conclusive evidence that the virus can be transmitted directly from camels to humans.
The report, published online June 4 in the New England Journal of Medicine (doi:10.1056/NEJMoa1401505) by Esam I. Azhar, Ph.D. and his colleagues at King Abdulaziz University Hospital, in Jeddah, Saudi Arabia, describes a 44-year old Saudi man who, in late October 2013, had applied medicine to the nasal passage of a camel with rhinorrhea.
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Direct cross-species transmission had probably occurred between the man and the camel without any intermediate host, the researchers wrote.
After becoming ill with respiratory symptoms a week later, he was hospitalized, and investigators visited his stables to collect nasal fluid and blood samples from his animals. Nasal swabs revealed active MERS-CoV infection in one of the nine camels the man owned, and serologic samples from other camels in his herd showed evidence of recent prior infection, at a time when serum screening by immunofluorescence assay had yet to reveal MERS-CoV antibodies in the patient. This meant, the researchers noted, that the camels had been infected before the patient.
Using nasal swab samples, Dr. Azhar and his colleagues carried out reverse-transcriptase–polymerase-chain-reaction detection, isolation, and sequencing of MERS-CoV from the camel with active infection and the patient. Viral isolates from both camel and human were shown to be identical on genetic sequencing. Previously, antibodies cross-reactive to MERS-CoV had been identified in camels, but without isolation and comparison of virus from both animal and human, the camels’ role as reservoirs or intermediate hosts for transmitting the virus to humans could not be confirmed.
In this case, Dr. Azhar and his colleagues wrote in their analysis, "direct cross-species transmission had probably occurred between the two without any intermediate host." The patient died after 2 weeks’ hospitalization, but all of his animals appeared to have cleared the virus following acute infection, suggesting that camels act only as transient hosts of the virus. "The exact reservoir that maintains the virus in its ecologic niche has yet to be identified," the investigators wrote.
None of the study’s authors reported conflicts of interest.