There are four globally endemic human coronaviruses which, together with the better known rhinoviruses, are responsible for causing common colds. Usually, infections with these viruses are harmless to humans.

DZIF Professor Christian Drosten, Institute of Virology at the University Hospital of Bonn, and his research team have now found the source of "HCoV-229E", one of the four common cold coronaviruses - it also originates from camels, just like the dreaded MERS virus.

The Middle East respiratory syndrome (MERS) coronavirus was identified in humans for the first time in 2012. It causes severe respiratory tract infections that are often fatal. Dromedaries were confirmed to be its animal source some time ago.

"In our MERS investigations we examined about 1,000 camels for coronaviruses and were surprised to find pathogens that are related to 'HCoV-229E', the human common cold virus, in almost six percent of the cases," says Drosten.

Further comparative molecular genetic analysis of common cold viruses in bats, humans and dromedaries suggests that this common cold virus was actually transmitted from camels to humans.

Common cold virus evolution could provide a scenario for MERS emergence

Drosten and his team isolated live camel common cold viruses and discovered that these could principally also enter human cells - via the same receptor used by the common cold virus "HCoV-229E". However, the human immune system is able to defend itself against the camel viruses, just as it can against common cold viruses.

Furthermore, tests with human serum and animal common cold viruses showed that there is no immediate risk of an epidemic in humans, because largest part of the human population already has immunity, owing to the widespread immunity against the common cold virus HCoV-229E.

So is this the all-clear for MERS viruses too? "The MERS virus is a strange pathogen: smaller, regionally restricted outbreaks, for example in hospitals, keep occurring. Fortunately, the virus has not adapted well enough to humans, and has consequently been unable to spread globally up to now," says Drosten.

The results of the current investigations on predecessors of the human HCoV-229E virus in camels depict a situation that is similar to the current situation with MERS. These predecessor viruses are also not optimally adapted to humans.

The global spread of HCoV-229E through human-to-human transmission, which is highly likely to have occurred during a past pandemic, gives rise to concern.

"Our current study gives us a warning sign regarding the risk of a MERS pandemic - because MERS could perhaps do what HCoV-229E did." So there is need for action: DZIF researchers are working intensively on researching a vaccine against MERS; it will go into clinical testing early next year.

"Link of a ubiquitous human coronavirus to dromedary camels" PNAS, Early Edition, DOI: 10.1073/pnas.1604472113.