The autopsy determined the cause of death Stella: pneumonia. Some time later, the results revealed that the culprit had been a human virus, specifically, a metapneumovirus. It usually causes us a simple cold, but Stella She wasn’t human, she was a chimpanzee. In 2017, that outbreak claimed her and 12% of her community in Kibale National Park, Uganda. That’s not counting the orphans who didn’t manage to survive.
This was not the first time it had happened. In Kibale, respiratory diseases have been the leading cause of death for chimpanzees for more than 30 years. And it’s not the only place. Chimpanzees in Taï National Park in Ivory Coast, those in Mahale Mountains National Park in Tanzania, and the delicate population of mountain gorillas in Virunga in Rwanda have also suffered outbreaks. In 2018, a literature review documented 33 probable or confirmed cases of pathogen transmission from humans to great apes.
Habitat destruction has brought us closer to wildlife, also affecting our microorganisms. There are even wild chimpanzees with bacteria resistant to antibiotics. For example, a study published in 2021 found that in Gombe National Park, in Tanzania, these apes have bacteria resistant to sulfonamides, a type of antibiotics used by human communities in the region to treat diarrhea.
Even so, until recently primate diseases were not considered a serious threat to their conservation. At the beginning of the millennium, the scientific community focused mainly on habitat loss and hunting, which continue to be very serious problems for primates. Modern humans have this tendency to cut down forests (the majority habitat of primates) and hunt wild animals. So far this century, 600,000 km² of tropical forest have been lost in the world, that is, an entire Iberian Peninsula. And in Central Africa alone, between one and four million tons of bushmeat are hunted each year.
Twenty years later, the transmission of pathogens from humans to animals, known as reverse zoonosis, has also come to be considered one of the most important threats to primates. Being so similar to us, this is a particularly vulnerable group.
A 2022 review found 97 studies documenting cases of reverse zoonosis in wild animals, of which 57 were primates. Curiously, the rest of the animals on the list were mostly charismatic species such as elephants or parrots. What does this tell us? According to the authors of the review, “this bias confirms that the observation of human pathogens in animals depends largely on the attention we pay to them.”
Unfortunately, this is another disadvantage for primates. The fact that there are people paying a thousand dollars to see free gorillas in Rwanda says it all. Therefore, it is not surprising that 82% of these infected primate populations were in captivity or being visited by tourists. When properly regulated, ecotourism provides a source of income that benefits local communities and can be used to encourage conservation efforts. But these data warn us that it is a double-edged sword.
In 2015, the International Union for Conservation of Nature (IUCN) published guidance to regulate great ape tourism. He recommended the use of masks, that the maximum number of tourists per group be less than nine, that the hours of observation be limited to one and that a minimum space of seven meters be left between the tourist and the animal.
The problem is that in practice, these measures are not followed as they should. That’s what a study published in 2020 revealed. We all know how much we like to brag on the internet. If we travel to Uganda and pay a fortune to see gorillas, we want the video to show us having the best experience. The study analyzed the videos that were shared on networks and found that in 40% the humans came within less than one meter of the gorillas.
Regarding captive primates, the majority of documented outbreaks were tuberculosis. Humans are the natural host of the bacteria that causes this disease, called Mycobacterium tuberculosis. However, primates are also very vulnerable, which is why we have been using them as experimental models to study this disease for years.
It is unknown to what extent tuberculosis may also be affecting wild populations, although there are some confirmed cases. In Taï National Park, a routine necropsy was performed on a chimpanzee who had been attacked by a leopard. Researchers found that she was infected with tuberculosis, although they could not determine whether it was a new strain specific to chimpanzees or had been transmitted from humans.
It must be said that the authors of the previously mentioned 2022 review were very conservative with the cases they included in their list. Only those in which it could be proven that the contagion had been from humans to animals were counted. For example, they decided to exclude all diseases that are transmitted by mosquitoes, such as yellow fever.
Yellow fever evolved in Africa about 1,500 years ago, where primates have developed resistance. Unfortunately, 300 years ago, this disease was introduced to America with the slave trade. And the primates there were not prepared, or so the thousands of monkeys that have died since then from yellow fever seem to tell us.
One of the most famous cases is that of the golden lion tamarin. At the beginning of the 70s, this beautiful primate was on the brink of extinction, with barely 200 individuals remaining. His luck began to change when the Mico León Dorado Association promoted the creation of a reserve to protect it. They had the collaboration of 150 zoos around the world in a captive breeding program to reintroduce them to the reserve during the 1980s. The population began to recover and in 2014, there were 3,700 individuals. However, two years later, there was an outbreak of yellow fever in Brazil that in a few months killed a third of the golden lion tamarins. It was a tragedy. Were all conservation efforts going to be in vain due to disease? Does this mean there is no hope for primates? Is it better to throw in the towel?
Of course not. With each passing year, conservation efforts increase, and we can find hope in small victories. In the 1980s, there were only 300 gorillas left in the Virunga Mountains, but in 2018 1,063 were counted. In turn, scientists have adapted the human yellow fever vaccine and a campaign has begun to vaccinate New World monkeys. As we all gain greater understanding and awareness of the issues, it is likely that incidents will become less and less frequent.
As one of the people who has fought the most for conservation said: “Human beings are an extraordinary creature, but the way we achieved it does not matter. Evolution itself is meaningless if we are not able to do great things with who we are now” (Jane Goodall).
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