A study published in the Centers for Disease Control and Prevention journal Emerging Infectious Diseases by Memish et al. analysed the presence of coronaviruses (including MERS-CoV) in 1 003 samples from wild bats collected in October 2012 and April 2013 in Saudi Arabia. Samples were collected in Bisha, Saudi Arabia, close to where the first patient with MERS-CoV was identified in September 2012 and in other regions where MERS-CoV cases have been found. Multiple alpha and beta coronavirus sequences were identified in 220 of 732 roost faeces samples and 7 of 91 rectal swab samples or faecal pellets. One amplified sequence of MERS-CoV from a T. perforatus bat captured in October 2012 in Bisha matched 100% with the MERS-CoV cloned from the index-case patient in Bisha.
The authors conclude that bats might play a role in human infection although this does not exclude the possibility of other hosts.
ECDC comment, 26 August 2013:
Identifying the host/s and source of MERS-CoV is urgently needed to prevent further infections and spread of the disease. Bat species are a well-known reservoir of coronaviruses and the study by Memish et al. confirms this.
While the results from the study are intriguing, there are several limitations that might limit a conclusion that bats are the direct source of MERS-CoV in humans. In this study a total of 1 003 different samples were collected from 110 bats captured during two samplings (October 2012 and April 2013); of those 227 samples tested positive for coronavirus, only one was found positive for the human MERS-CoV. The information about the viral load of the MERS-CoV positive sample is missing and the failure of further sequencing might lead to the speculation of a very low virus load in the sample. The amplified bat MERS-CoV sequence was very short and lies within a conserved region of the genome; however, a divergence within other genomic regions cannot be ruled out. Furthermore the MERS-CoV sequence amplification product of this positive sample was retrieved only from newly established generic MERS-Coronavirus (nested RdRp) assay, while the World Health Organization recommended MERS-CoV specific assays were negative.
All coronavirus sequences were detected in faecal pellets or from roost faeces but not from serum, throat swab samples, or urine. It is unclear if other samples from this particular MERS-CoV positive animal were also available and tested in this study. The possibility of transmitting virus via faeces from bats to humans has been discussed for rabies (Gibbons 2002, Johnson, Phillpotts et al. 2006) and might also been a route of transmission for MERS-CoV. Just as people have been infected with hantavirus while sweeping-up dried mouse droppings, humans (and camels) could be infected by inhaling dust mixed with dried contaminated bat, or other animal, excrement (Jonsson, Figueiredo et al. 2010, Richardson, Kuenzi et al. 2013).
This, and the study by Reusken et al. (Reusken, Haagmans et al. 2013) cited in the ECDC Public Health Development of 12 August 2013
, provide evidence that MERS-CoV might be a zoonotic disease but it is still not clear how the disease progresses from animals to humans. The epidemiological investigations have so far excluded direct animal contact as the probable route of infection for most MERS-CoV patients, but indirect mechanisms could be involved.
The previously published ECDC risk assessment is still valid.
Memish ZA, Mishra N, Olival KJ, Fagbo SF, Kapoor V, Epstein JH, et al. Middle East respiratory syndrome coronavirus in bats, Saudi Arabia. Emerg Infect Dis [Internet]. 2013 Nov [date cited]. http://dx.doi.org/10.3201/eid1911.131172
Gibbons, R. V. (2002). "Cryptogenic rabies, bats, and the question of aerosol transmission." Ann Emerg Med 39(5): 528-536.
Johnson, N., R. Phillpotts and A. R. Fooks (2006). "Airborne transmission of lyssaviruses." J Med Microbiol 55(Pt 6): 785-790.
Jonsson, C. B., L. T. Figueiredo and O. Vapalahti (2010). "A global perspective on hantavirus ecology, epidemiology, and disease." Clin Microbiol Rev 23(2): 412-441.
Reusken, C. B., B. L. Haagmans, M. A. Muller, C. Gutierrez, G. J. Godeke, B. Meyer, D. Muth, V. S. Raj, L. S. Vries, V. M. Corman, J. F. Drexler, S. L. Smits, Y. E. El Tahir, R. De Sousa, J. van Beek, N. Nowotny, K. van Maanen, E. Hidalgo-Hermoso, B. J. Bosch, P. Rottier, A. Osterhaus, C. Gortazar-Schmidt, C. Drosten and M. P. Koopmans (2013). "Middle East respiratory syndrome coronavirus neutralising serum antibodies in dromedary camels: a comparative serological study." Lancet Infect Dis.
Richardson, K. S., A. Kuenzi, R. J. Douglass, J. Hart and S. Carver (2013). "Human exposure to particulate matter potentially contaminated with sin nombre virus." Ecohealth 10(2): 159-165.
ECDC staff who contributed to the public health development:
Cornelia Adlhoch, Elizabeth Bancroft, Andrew J Amato-Gauci, Denis Coulombier