The thrill of hacking through dense African forest in search of the majestic mountain gorilla is an eco-tourist’s dream. And for those fortunate enough to encounter these great apes, it is a memorable highlight to be captured in photographs and shared later with family and friends.

Ape tourism has never been more popular, despite the high costs. Tens of thousands of visitors each year are willing to pay fortunes to commune with nature. But scientists are growing increasingly alarmed following the publication of evidence that great apes are dying from respiratory viruses directly transmitted to them by humans. They fear that existing safety measures to protect the animals do not go far enough and are calling for stricter precautions, including the mandatory wearing of face masks for all who come into close contact with gorillas, orangutans and chimpanzees.

Their concern follows the first evidence that chimpanzees in Ivory Coast, west Africa, died from HRSV (human respiratory syncytial virus) and HMPV (human metapneumovirus) during outbreaks at the Taï chimpanzee research station. The findings pose a major problem for those protecting the declining populations of gorillas in Uganda, Rwanda and the Democratic Republic of Congo, now numbering less than 650, as well as orangutans in Borneo, thought to number around 15,000. The tourist dollar is essential. It protects the endangered apes from poachers and funds vital work aimed at halting their decline. But this positive aspect of eco-tourism must now be balanced against the negative side-effects if apes, and ape tourism, are to survive.

One of the problems is that tourists may not know they are carriers of the viruses, as there are often no symptoms. The only way to eradicate risks is by the wearing of masks, such as the N95 masks recommended for protection against avian flu. Scientists want to increase the distance that tourists are supposed to keep from the apes from seven metres to at least 10 metres. And they are calling for tourists and research workers alike to produce proof of vaccinations and to disinfect all clothing and footwear before being allowed near the animals.

The new measures are proposed by Fabian Leendertz, a wildlife epidemiologist at Berlin’s Robert Koch-Institut and senior author of the new report, Pandemic Human Viruses Cause Decline of Endangered Great Apes. To date only bacterial and parasitic infections of typically low virulence have been shown to move from humans to wild apes, he said. “This is the first evidence of direct virus transmission. It has been suspected before, but this is the first real proof. Although our research applies to chimpanzees, the risk to gorillas and orangutans is exactly the same.”

He said that a seminar was planned with major ape tourism operators to discuss ways to implement new safety measures. “If you have spent all that money, the very least you want is a photograph of yourself with the gorillas. And the photograph doesn’t look as good if you have to wear a mask,” he said. “But we hope the type of people who go on these holidays will take that responsibility.”

Jo Setchell, a primatologist at Durham University and member of the Primate Society of Great Britain, who backed the calls for more stringent precautions, said: “It is very concerning. It is something that has been raised before, but this is the first report that really demonstrates concretely that these viruses are transmitted by humans.”

The findings follow a 10-year research project at the Taï station during which 15 young chimpanzees died in three outbreaks. It showed the viral strains sampled from the apes were closely related to strains circulating in human epidemics. Tourists visiting gorillas are warned not to trek if they have symptoms of a cold, to turn away from the animals to cough, not to spit in the parks and to bury faeces. But tourists may be unwittingly infected with respiratory viruses before symptoms present themselves.

“I think the masks are essential,” said Setchell. “One of the major problems is if you go on a fairly short holiday to, say, Uganda, and you have paid a lot for your permit, if you have a slight cold many people will not forgo that money. They’ll take medication to hide their symptoms — because it’s a big tourist experience, they have waited a long time for it, and it is very expensive.

The Observer