An estimated three-quarters of camels recently surveyed in Saudi Arabia have evidence of infection with the Middle East Respiratory Syndrome coronavirus (MERS-CoV), the virus responsible for human cases of MERS. Results of the new study establish for the first time that direct camel-to-human transmission is possible and provide a pathway to control the spread of the disease.
Results in the journal mBio are reported by scientists at the Center for Infection and Immunity at Columbia University's Mailman School of Public Health; Mammals Research Chair, King Saud University, Riyadh, Saudi Arabia; the National Institute of Allergy and Infectious Diseases at the National Institutes of Health; and EcoHealth Alliance.
To date, at least 182 people have been infected with the virus that causes MERS and 79 have died since the first documented case in Saudi Arabia in September 2012. Since then, most cases have been in Saudi Arabia, with lower numbers in Jordan, Qatar, Tunisia, and the United Arab Emirates. France, Germany, Italy, and the United Kingdom have also reported cases related to travel to the Middle East. So far the source of the disease has remained a mystery.
An analysis of blood samples collected from 203 camels across Saudi Arabia in 2013 found 150, or 74%, had antibodies to the MERS coronavirus, indicating past infection. Nasal swabs and rectal specimens revealed that genetic sequences of MERS-CoV from active infection in camels matched those found in humans. The rate of camels with active MERS-CoV infection varied widely by region, ranging from 66% of camels in Taif in the west to none in Gizan in the southwest. Young camels were more than twice as likely as adults to be infected. No evidence of MERS was seen in a similar survey of sheep and goats.
"This study is the first to show that the MERS virus seen in humans is widespread in camels throughout Saudi Arabia," says first author Abdulaziz N. Alagaili, PhD, the director of the Mammals Research Chair at King Saud University. "This information is crucial for efforts to contain the spread of the disease. To this end, I want to thank His Excellency Minister of Higher Education Dr. Khalid Al Anqari; His Highness Prince Bandar bin Saud Al Saud, president of the Saudi Wildlife Authority, and Professor Badran Alomar, president of King Saud University, for their continued support of this important project."
Airborne transmission of the virus between camels is most likely based on a number of clues, including that the virus was more evident in nasal swabs as opposed to rectal specimens. But how humans get the disease has not yet been determined.
"What we know now is that camels carry the same MERS virus that infects humans, which indicates that they have the potential to transmit the virus directly to humans," says study co-author Thomas Briese, PhD, associate director of the Center for Infection and Immunity and associate professor of epidemiology at the Mailman School.
"A study we published last year found that the virus was carried in a bat found near the first known human case of MERS," adds Dr. Briese. "The roles of bats and camels in human infection remains an area of active research for our group and others."
MERS-CoV in Camels Since 1992 or Earlier
MERS-CoV has been carried by camels in Saudi Arabia for more than 20 years, and likely longer. The researchers looked at blood serum samples from camels, finding evidence of the virus dating back to 1992, the earliest sample. MERS is not fatal in camels and there are so far no outward signs of the disease, although researchers say the animal's characteristic drool could be related.
Human cases of MERS-CoV may have a longer history than previously thought. Before the index case in 2012, they may have been labeled as a more generic "unexplained respiratory disease." Unfortunately there are no available human samples to test the hypothesis.
New Mobile Lab, Saudi Collaboration
Alongside its insights into MERS-CoV, the study also cemented collaborations and validated systems that will carry forward into future studies of MERS-CoV and other infectious disease threats.
"The study is the first collaboration between the Center for Infection and Immunity and King Saud University, as well as the first to use the Center's new mobile field laboratory, that is designed to enable surveillance, discovery and service missions in support of international organizations like the World Health Organization," says senior author W. Ian Lipkin, MD, director of the Center for Infection and Immunity and the John Snow Professor of Epidemiology at the Mailman School. "We look forward to continued work toward to ultimate goal of eliminating the threat of MERS and other infectious agents to human health."