It is now a year since the latest variation of the coronavirus, Mers, manifested itself in the human population in Saudi Arabia. But unlike Sars, the virus seems not to show a propensity to mutate into a form that could cause a pandemic and appears to be dying out slowly. Indeed, it may only be today's sophisticated testing techniques that led to it being identified in the first place.
Whenever a previously unidentified virus occurs in humans, the search begins to identify the source. Mers is thought to have originated in bats in Saudi Arabia and to have been passed to humans via an intermediary animal: possibly the dromedary camel, although sheep, goats and cattle are also being tested.
Bats are a known source of a number of human virus infections, including Ebola, heniphavirus, rabies and Sars, but they are not the only culprits and because they have little interaction with the human population they are not deemed to be a particular danger.
The latest animal to come under scrutiny is the harbour seal in the US, following the deaths of 162 of the animals in New England last year. Scientists identified a new strain of influenza virus, H3N8, which is closely related to a strain circulating in North American birds since 2002. According to the scientists the virus has the ability to target a protein found in the human respiratory tract.
The risk from animal viruses is difficult to assess. Research carried out by the Center for Infection and Immunity at the University of Columbia in the US and published in the journal mBio suggests that there could be 320,000 undiscovered viruses that are circulating in animals. Although not all of these, or even most of them, will be transmissible to humans, identifying them is the first step to mitigating the risk.
But knowing where the virus comes from is only half the story – understanding the actions and interactions that lead to human infection is even more important if a pandemic is to be prevented or at least contained.