MERS-CoV, the Middle Eastern Respiratory Syndrome coronavirus, continues to cause infections (often fatal) and confusion. For a while now, there’s been speculation that camels are the source of this virus, based in part on how commonly antibodies against the virus (or a related virus) are found in healthy camels. It always seemed strange, though, for camels to be the ultimate source, leaving lingering questions about whether there is another source or where camels got exposed to the virus in the first place.
Some have focused their attention on bats (which were ultimately the source of the related SARS-coronavirus). A recent paper in the Journal of Virology (Corman et al 2014) helps answer some of those lingering questions questions. The researchers found a coronavirus in the feces of a South African Neoromicia capensis bat. When they looked at the sequence of the virus’ genome, it was quite similar to that of MERS-CoV – close enough that the two viruses would be considered the same species. There were some differences, though, indicating there appears to be a "bat type" and a type that infects people and camels.
Relatedness is one thing, but figuring out how viruses are different and when they diverged is important (i.e. did the camels get the virus from the bats, or did the bats get it from the camels?). From an evolutionary standpoint, the bat virus "roots" the phylogenetic tree of human and camel MERS-CoV, meaning that when the different viruses are shown in their "family tree" based on their genetic makeup, the bat coronavirus is the one that comes up at the common ancestor. So, it appears that MERS-CoV originated from this bat virus.
The genetic relatedness of these viruses, the fact that the bat virus appears to be the ancestor, and the evidence for circulation of MERS-CoV in camels for at least 20 years suggests that:
- The virus jumped from bats to camels in the southern part of Africa a few decades ago,
- It was imported to the Arabian peninsula (since that is a common route of camel movement), and
- It recently started to infect people.
There was also the suggestion that camels may be a "mixing vessel" for different coronaviruses, like pigs are for influenza viruses, but I think that’s pretty speculative.
For me, a few questions remain:
- Why is MERS not detected in southern Africa, if that’s where the related virus is present in bats and where it presumably made the jump to camels?
- Why has MERS only recently been identified in people when its been present in camels for a few decades?
As is typically the case with infectious diseases, a few nice answers lead to many more questions. Presumably, lots of camels, bats and other species will continue to be tested in Africa and the Middle East to see what other information can be learmed.