Update on MERS-CoV transmission from animals to humans, and interim recommendations for at-risk groups
Updated on 26 January 2018
Several investigations into the animal source of Middle East respiratory syndrome coronavirus (MERS-CoV) have identified dromedary camels (Camelus dromedaries, dromedaries) as the natural reservoir for MERS-CoV.
Since 2012, MERS-CoV genetic sequences from humans and dromedaries in Egypt, Oman, Qatar, Saudi Arabia, and United Arab Emirates demonstrate a close link between the virus found in dromedaries and the virus found in people in the same geographic area. Several additional studies from the Canary Islands, Egypt, Jordan Saudi Arabia, Qatar, Kenya, Oman, United Arab Emirates and Pakistan have identified high levels of MERS-CoV specific seroprevalence in dromedaries.
Results from an investigation in Qatar in 2014 showed that people working closely with dromedaries (e.g. farm workers, slaughterhouse workers and veterinarians) may be at higher risk of MERS-CoV infection than people who do not have regular close contacts with camels. In Qatar, Saudi Arabia and several other countries, other animals, including Bactrian camels (Camelus bactrianus), goats, cows, sheep, water buffalo, swine and wild birds, have been tested for antibodies to MERS-CoV, with no positive results. Alpacas, llamas and goats have been shown to develop antibodies when experimentally infected. The absence of MERS-CoV specific antibodies in naturally infected animals indicates that the likelihood of other animals having a substantial role in transmission of MERS-CoV is very low. The collective surveillance and research studies to date, in addition to data gathered on the exposures of community acquired cases of MERS-CoV infection, provide ample evidence that dromedaries are the primary source of the MERS-CoV that is infecting humans. The studies conducted to date, however, have not identified the specific exposures or mode(s) of transmission responsible for dromedary to human transmission.
The current pattern of disease in humans appears to be the result of repeated introductions of the virus from dromedaries to people, resulting in limited human-to-human transmission, but not in sustained transmission. Therefore, discovery of the routes of transmission, whether direct or indirect, between dromedaries and people, is critical to stopping transmission of the virus.
WHO is working with partner agencies with expertise in animal health and food safety, including FAO, OIE and national authorities, to facilitate ongoing investigations.
As a general precaution, anyone visiting farms, markets, barns or other places where dromedaries are present should practice general hygiene measures, including regular hand washing after touching animals, avoiding touching eyes, nose or mouth with hands, and avoiding contact with sick animals. People may also consider wearing protective gowns and gloves while professionally handling animals.
The consumption of raw or undercooked animal products, including milk, meat, blood and urine, carries a high risk of infection from a variety of organisms that might cause disease in humans. Animal products processed appropriately through proper cooking or pasteurization are safe for consumption but should also be handled with care, to avoid cross-contamination with uncooked foods.
Studies in Qatar show that MERS-CoV can be detected in raw milk from infected dromedaries. Whether dromedaries excrete MERS-CoV in milk or the virus gets into the milk through cross-contamination during milking is unclear. However, if MERS-CoV is present in milk or other dromedary products, it will be destroyed by pasteurization or cooking. Dromedary meat and dromedary milk are nutritious products that can continue to be consumed after cooking, pasteurization, or other heat treatments. Safe alternatives should be developed to the tradition of sales of raw dromedary milk for direct consumption, along roadsides and farm gates.
Recommendations for at-risk groups
Until more is understood about MERS, people with diabetes, renal failure, chronic lung disease, obesity, and immunocompromised persons are considered at high risk of severe disease from MERS-CoV infection. Therefore, individuals with these underlying medical conditions should avoid contact with dromedaries, should not drink or use raw dromedary milk, blood or urine, and should not eat meat that has not been properly cooked. Such recommendations should also be disseminated to travellers, tourists and pilgrims with above mentioned underlying conditions coming to the region from around the world.
Results from several seroprevalence studies of individuals working with dromedaries indicate that people handling or working with dromedaries are at increased risk of infection with MERS-CoV compared with people who do not have contact with dromedaries. Until more evidence is gathered, it is prudent for dromedary farm workers, slaughterhouse workers, market workers, veterinarians and those handling dromedaries at racing facilities to practice good personal hygiene, including frequent hand washing after touching animals. They should wear facial protection where feasible and protective clothing, which should be removed after work and washed daily.
Workers should also avoid exposing family members to soiled work clothing, shoes, or other items that may have come into contact with dromedary excretions. It is therefore recommended that these clothes and items remain at the workplace for daily washing and that workers have access to and use shower facilities at their workplaces before leaving the premises.
Dromedaries infected with MERS-CoV may not show any signs of infection. It is therefore not possible to know whether an animal in a farm, market, race track or slaughterhouse is excreting MERS-CoV that can potentially infect humans. However, infected animals may shed MERS-CoV through nasal and eye discharge, faeces, and potentially in their milk and urine. The virus may also be found in the organs and meat of an infected animal. Therefore, until more is known about infection in animals, the best protection is to practice good hygiene and avoid direct contact with all of these. Obviously sick animals should never be slaughtered for consumption; dead animals should be safely buried or destroyed.
Unless protected, people should avoid contact with any animal that has been confirmed positive for MERS-CoV until subsequent tests have confirmed that the animal is free of the virus.