A couple of days back, I briefly spoke about the theories surrounding the origin of MERS-coronavirus on twitter and got interesting responses like “Batman!” during the discussion. (Let us not eliminate this possibility entirely, okay?) Middle Eastern Respiratory Syndrome, which was first reported in Saudi Arabia in September 2012 1, is similar to SARS, and causes severe respiratory illness with symptoms of cough, fever, and shortness of breath including acute renal failure which ultimately results in death of the infected individuals in fifty percent of the cases. So far, 150 cases have been reported by CDC 2, which include 64 deaths (most affected countries being Saudi Arabia, United Arab Emirates, Jordan and Qatar). What’s interesting is the quest to find the origin of the virus and it’s mode of transmission.
Since most viruses are harbored and transmitted by animals, a team of scientists first suspected the most plausible animal in the Middle-East that could’ve sheltered this virus – camels! Antibodies against MERS-CoV (and not the virus itself) were found in some retired racing camels in Oman 3. The specificity of the antibodies against MERS were tested positive in every single camel but none of the animals had antibodies against SARS. These false positive results further raises questions about camels being the original animal reservoir of the virus .
Bats are the next key suspect because viruses related to MERS are found in several bats species. More specifically, SARS-CoV comes from bats. These mammals are also the reservoir for Nipah virus, Hendra virus, Rabies virus, Ebola virus, and Marburg virus – all of which belong to other families. Not surprisingly, Columbia University virologist Dr. W Ian Lipkin found a 187-nucleotide RNA fragment in the feces of an Egyptian tomb bat that exactly matched the corresponding sequence in MERS-CoV 4 that was isolated from one of the victims. A possible theory is that humans may have been infected with the virus by coming in contact with bats’ feces during encroachment of old abandoned buildings, which serve as a natural habitat for tomb bats. However, Dr. Lipkin does not think that the bats could’ve infected humans directly 5. Here’s where the camels from Oman come into picture, by acting as an intermediate host for the virus. The virus could’ve been transmitted to camels through the bats’ droppings. Humans and camels posses a close relationship in the Middle-East where the animals of burden, used for their meat and milk, are imported from other countries. An alternate possible explanation is that the virus might have originated in bats from one of these countries, hitchhiked on the exported camels and spread in the Middle-East.
Given only the small sampling of camels and bats in these countries so far, one can speculate the existence of other hosts for the virus. Perhaps there are other missing links in the chain of transmission. Other bats & wildlife species and domestic animals for CoV infection, and their link to humans must be investigated. It is a situation of race against time for scientists when a new virus emerges faster than our understanding.
- Zaki AM, van Boheemen S, Bestebroer TM, Osterhaus AD, Fouchier RA. 2012. Isolation of a novel coronavirus from a man with pneumonia in Saudi Arabia. The New England Journal of Medicine. 367: 1814 – 1820
- MERS webpage on CDC – http://www.cdc.gov/coronavirus/mers/
- PubMed Health News Article – http://www.ncbi.nlm.nih.gov/pubmedhealth/behindtheheadlines/news/2013-08-09-camels-may-be-source-of-mers-virus-transmission/
- Memish ZA, Mishra N, Olival KJ, Fagbo SF, Kapoor V, Epstein JH, et al. Middle East respiratory syndrome coronavirus in bats, Saudi Arabia. Emerging Infectious Diseases. Vol 19. November 2013
- Dr. Ian Lipkin for Science – http://news.sciencemag.org/health/2013/08/bat-out-hell-egyptian-tomb-bat-may-harbor-mers-virus