杏吧原创

As if poaching, logging, habitat loss and climate change aren鈥檛 bad enough, wild chimpanzees now face a new, deadly peril: a virus that causes common colds in people. The threat has been exposed after an investigation of an outbreak of respiratory disease that struck chimps in 2013.

The outbreak occurred in the Kanyawara community in Uganda鈥檚 . Out of 56 chimpanzees, five died: almost 10 per cent of the population.

A detailed post mortem on a two-year-old chimp called Betty, who died of severe pneumonia, demonstrated almost beyond doubt that human rhinovirus C was to blame. Genes from human rhinovirus C were found throughout Betty鈥檚 fluid-filled lungs and respiratory tract. No other viruses or infectious agents were detected.

鈥淚t was the smoking gun in that animal, a virus that shouldn鈥檛 be there, and no others,鈥� says lead author of the University of Wisconsin-Madison. 鈥淲e think this human common cold virus represents a grave threat to chimpanzees all across Africa.鈥�

A history with humans

Unlike cold rhinoviruses A and B, rhinovirus C poses a special threat because it evolved relatively recently in humans. It caused widespread infant mortality from around 8000 years ago, when the rise of farming drove people to live closer together.

Half the human population now has immunity to rhinovirus C. However, many still carry a variant of the CDHR3 gene that makes them especially susceptible, intensifying symptoms and raising the risk of childhood asthma.

The gene makes a receptor on cells in the respiratory tract. Research in humans suggests that, in those with the harmful variant, rhinovirus C binds much more strongly to the receptor. It can then infect cells and spread more rapidly, and produces 10 times more virus per cell than usual.

Vulnerable chimps

Goldberg鈥檚 team found the same susceptibility variant 鈥� called CDHR3-Y₅₂₉ 鈥� in the faecal DNA of all 41 sick chimps they tested. Worse, they found it in all reference samples of DNA from 24 chimps throughout Africa, collected through the pan-African .

鈥淲hen people lived closer together 8000 years ago these viruses really took off, but we鈥檝e evolved genetic resistance,鈥� says Goldberg. 鈥淐himps have not had that benefit, so as far as we can tell every chimp in Africa is susceptible.鈥�

Goldberg says long-term records at Kanyawara show undiagnosed respiratory disease outbreaks have been occurring twice a year for at least the past decade, with fatalities roughly every two years.

Epidemics of undiagnosed respiratory disease have also been recorded elsewhere in Africa. They have been the dominant cause of death among chimps living in Gombe, Tanzania for almost 50 years, accounting for 48 per cent of all fatalities.

Don鈥檛 get too close

Viruses that are mild in people, or produce no symptoms at all, pose the greatest risk to apes. That鈥檚 because visitors to the forests don鈥檛 realise they鈥檙e infectious, says of the Robert Koch Institute in Berlin, Germany. In 2008 he discovered that chimps are being killed by human metapneumovirus. 鈥淥nce you have severe influenza, you won鈥檛 walk to the forest any more, luckily for the great apes.鈥�

Goldberg says the threat is no reason to halt ecotourism, which brings valuable revenue to Africa and to conservation. But visitors, rangers and conservation staff should take greater precautions to prevent infection. That could include wearing masks and keeping a set distance from the animals.

鈥淚t鈥檚 amazing to me that many field sites still don鈥檛 respect hygiene rules when working with great apes,鈥� says Leendertz. 鈥淭hey鈥檙e clearly published by us and others and found in .鈥�

Chimpanzees are already . Their numbers globally have shrunk dramatically to , down from as many as 2 million a century ago. The spread of the human cold could make things even worse for them.