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The Role of Camels in MERS Transmission

Amesh A. Adalja, MD, FACP, FACEP, February 6, 2015

The emergence of novel infectious diseases is usually suspected, for good reason, to be of zoonotic origin, since animal species are the reservoir for myriad infectious diseases. 

The MERS coronavirus, which has been spreading in the Middle East since 2011, is likely to have originated in bats, spread to camels, and then spilled into the human species. Evidence of the virus’s presence has been widely documented in camels, but it still remains somewhat unclear how the disease makes its way into humans and how frequently it does so. A new study published in Emerging Infectious Diseases attempts to answer those questions.

 

Infected Camel Herd

The study by Hemidi et al centered on an infected dromedary camel herd known to harbor the MERS virus. Serum samples from 191 people with no history of clinical MERS but with varying degrees of exposure to the camels were assayed for evidence of prior MERS infection. The individuals were categorized into 5 tiers of exposure ranging from those who frequently consumed unboiled camel milk to those with no exposure, who served as the negative control group. Surprisingly, none of the 191 samples tested displayed evidence of infection.

 

Limited Understanding of Transmission

The authors note that these findings do not mean that camels are not involved in the spread of MERS but rather that transmission of MERS from camels to humans is not a straightforward event and that many poorly understood variables may play a role in viral spillover. For example, all infectious diseases are the result of an interaction between a host and a microbe, but not all hosts may be equally susceptible. 

Another implication is that, although camels can be infected with MERS, human-to-human transmission may play a bigger role than previously thought in the virus’s spread. While nosocomial transmission of MERS has been clearly documented, the role of community transmission is much less clear. 

More studies focused on the epidemiology of non-nosocomial infection clusters with detailed attention to interactions with camels will be needed to further elucidate the transmission dynamics of this virus. Questions regarding what interactions confer higher risk and whether there is a pattern of viral shedding in the camel would be important to answer. These answers should drive future epidemic control measures, including the development and use of a MERS vaccine for camels.

 

Reference

Hemida MG, Al-Naeem A, Perera RAPM, et al. Lack of Middle East Respiratory Coronavirus transmission from infected camels. Emerg Infect Dis 2015. http://wwwnc.cdc.gov/eid/article/21/4/14-1949_article. Accessed February 4, 2015.