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The current coronavirus pandemic, which likely jumped to humans from a market selling wildlife for meat, has shown us that zoonotic diseases pose an urgent threat to people around the world. At the same time, infectious diseases can also pass from humans to non-human animals, threatening wild animals who come into close contact with people. The news in April that five tigers and three lions at the Bronx Zoo tested positive for SARS-CoV-2, the virus that causes COVID-19, is a case in point: The big cats are believed to have been infected by an asymptomatic zoo employee.
Animals kept in captivity around the world — including in public zoos, private zoos, captive breeding facilities, and even wildlife sanctuaries — are at risk of becoming infected with SARS-CoV-2 and other pathogens from humans. So are animals in the wild that come in contact with humans via the wildlife tourism industry.
“It appears that the most common pathogens spread from humans to other animals are respiratory viruses and intestinal parasites,” explains Michael Muehlenbein, PhD, MsPH, professor and chair of the Department of Anthropology at Baylor University, Texas. “Those most at risk are arguably those most closely genetically related to us. We could predict that closely related mammals would be at higher risk compared with birds or reptiles, for example.”
Due to their genetic similarity to people, primates are especially susceptible to reverse zoonotic diseases and usually experience them more severely than people. For many people, a common cold may be a minor annoyance. For mountain gorillas, which are listed as endangered on the International Union for the Conservation of Nature (IUCN) Redlist, a cold could cause death, with broader implications for the species’ survival. Primates are largely social animals so pathogens can spread quickly. Many primate species also have slow reproductive rates, making it more difficult for populations to recover after suffering losses.
The Democratic Republic of Congo, Rwanda, and Uganda have suspended mountain gorilla tourism to protect gorillas from SARS CoV-2. It is not yet known whether great apes are susceptible to SARS CoV-2 but wildlife experts say that it safest to assume they are.
So far, there are no known cases of tourists infecting animals in the wild with the novel coronavirus and there is little information on the scale of reverse zoonosis in the wildlife tourism industry in general. This could be due to the difficulty in tracking down the source of diseases, or the lack of focus given to this issue. Research on zoonotic diseases largely focuses on transmission from animals to people.
“Humans are human-centric so we worry about our health and the health of our families,” states Jonna Mazet, executive director at the University of California Davis One Health Institute, which works globally to advance the health of animals, people and the environment. Mazet also notes that there is significantly more funding for human health research than wildlife health research.
“It is not possible to accurately calculate the risk of anthroponoses associated with tourism because we have not been monitoring this systematically,” explains Muehlenbein. “But many of the species we are visiting are critically endangered. Any risk above zero for those species is unacceptable.”
Before the current global lockdowns and social distancing measures were put in place, wildlife attractions were incredibly popular among travelers. Wildlife tourism accounts for 12 million trips annually and is growing about 10 percent every year. Many tourists desire close encounters, which can increase the risk of spreading disease. It can also cause increased stress in wild animals, in turn making them more susceptible to disease. International travelers may also bring unfamiliar pathogens that wild animals have not built an immunity against.
Wildlife tourism can have great benefits to wild animals when done right. It can fund conservation projects, protect habitats, raise public awareness, and help communities. For species like mountain gorillas, wildlife tourism may even be the key to their survival.
“Mountain gorilla tourism was initiated in the 1980s, when the population of gorillas was in decline due to poaching and habitat loss,” explains Dr. Kirsten Gilardi, executive director & chief veterinary officer of Gorilla Doctors. “Without a doubt, mountain gorilla tourism has saved the mountain gorilla from extinction: it provides the basis for designation of the gorilla’s forest habitat as protected, and generates the revenue needed for park management and protection.”
The Uganda Wildlife Authority has developed rules to protect mountain gorillas from over-exposure to humans, such as limiting the number of people on treks each day and mandating that tourists stay at least seven meters away from gorillas — a rule set in place because human sneezes can travel up to six meters.
Even with these rules in place, a study of mountain gorilla tourism encounters in Uganda’s Bwindi Impenetrable National Park found that tourists violated the seven meter rule in over 98 percent of treks. Tourists were within three meters of gorillas 14 percent of the time.
Tourists are not the only ones seeking contact, Gilardi explains. Gorillas sometimes approach tourists and it can be difficult for tourism operators to control these interactions.
A separate study examining tourists at Bwindi Impenetrable National Park found that 25 percent of tourists would consider gorilla trekking even if they were sick despite being aware of rules against this. For these tourists, the costs of traveling to visiting the gorillas outweighed concerns about gorilla safety.
Despite the risk posed by tourists, habituated mountain gorillas that come into frequent contact with humans are still believed to have better health outcomes than unhabituated gorillas due to daily monitoring and veterinary interventions they receive.
In a less regulated sphere of wildlife tourism, the feeding of wild animals by tourists has become a popular activity. These encounters can occur at captive wildlife facilities, but can also occur in the wild as animals learn to associate popular tourist hotspots with food. At a site in Morocco’s Ifrane National Park, tourists have been visiting monkeys for over ten years. The site now experiences high tourist volume and monkeys associate the area with getting fed. Researchers examining the site found that tourists often engaged in behaviors that increased the chances of disease transmission, such as cracking peanut shells in their mouths and giving them to monkeys and allowing monkeys to drink from their water bottles.
As the current pandemic continues to put travel to a halt, wild animals dependent on tourists for food have suffered. In March, video went viral depicting a large number of monkeys in Lopburi, Thailand reportedly fighting over food, illustrating how dependent the monkeys had become on tourists.
Dr. Tierra Smiley Evans, epidemiologist and wildlife veterinarian at the University of California Davis One Health Institute, notes that monkey temples in Asia are a potentially high-risk environment for the spread of SARS-CoV-2.
“That does concern me, these places where you have large populations of people coming from many different geographic regions and combining with large populations of macaques,” she explains.
Tigers, which are listed as endangered on the IUCN Redlist, are also common in the wildlife tourism industry and tourists visit tigers at captive facilities throughout the world. With the recent news that tigers are susceptible to COVID-19, wildlife advocates are raising additional concerns about cub petting attractions, where tourists can directly interact with tiger cubs. In April, The People for the Ethical Treatment of Animals petitioned the United States Department of Agriculture to issue an emergency rule banning public encounters with big cat cubs during the current coronavirus pandemic.
Muehlenbein believes that most wildlife tourism operators are not doing enough to protect wild animals from reverse zoonotic diseases. As he notes, there is no global regulatory body monitoring or enforcing regulations.
But there are steps that can be taken to protect wild animals. Simple practices such as not allowing direct interactions between humans and wild animals could greatly reduce the chances of transmission, experts state.
In mountain gorilla tourism, many of the recommended precautions are all too recognizable for people currently social distancing. The IUCN Species Survival Commission Primate Specialist Group recommends practices such as keeping distance from the gorillas, hand-washing, staying home if sick and wearing facemasks.
It is unclear how long the current pandemic will last. It is even less clear what kind of threat Covid-19 poses for wild animals in the tourism industry. Tourism is at a halt right now, but will likely pick up after Covid-19 has subsided. When that happens, precautions will be essential.
“I hope this COVID-19 outbreak is a reminder that we cannot let our guard down whenever we are dealing with wildlife tourism,” Smiley Evans states.
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