When humans transmit diseases to animals

Diseases transmitted from humans to animals threaten conservation efforts and can also become a health problem for humans through retransmission. The researchers reviewed published studies on the topic and identified nearly 100 cases in which human pathogens were detected in animals. Such alleged spills have been detected particularly frequently in primates and large zoo animals. The authors hypothesize that many other transmission events have been overlooked. AI can help predict high-risk species in the future.

There is a high possibility that the SARS-CoV-2 virus has jumped from bats to humans. Many other infectious diseases such as swine flu, bird flu, SARS and MERS are called zoonoses, that is, pathogens that are transmitted from animals to humans. Especially given the Covid 19 pandemic, this transmission path has received a great deal of public and scientific attention. However, the reverse trend could also be cause for concern: Pathogens can also be transmitted from humans to previously unaffected animal species.

Cases in zoo animals and primates

A team led by Anna Vagre of Colorado State University in the US studied this in more detail. “We searched the literature to see how the process played out in the past,” says co-author Gregory Albery of Georgetown University in Washington, DC. And in 97 published studies, researchers found reports of transmission of human pathogens to animals.

Almost half of the accidents detected concern animals in captivity, especially in zoos. However, because veterinarians closely monitor the health of zoo animals, they are more likely to detect a human-borne viral disease in their shipment than animals in the wild. In 57 out of 97 cases, the affected animals were primates. On the other hand, this is evident because apes are among the closest relatives of humans and therefore the jump of viruses is smaller than that of the most distant evolutionary species. On the other hand, great apes in particular are carefully monitored – both in zoos and in the wild.

Effects on animals and humans

“This supports the notion that we are more likely to discover pathogens as we dedicate a lot of time and effort to research, with a disproportionate number of studies focusing on charismatic animals in zoos or in close proximity to humans,” says Fagre. “This raises the question about what cross-species transmission events might be missing and what this might mean not only for public health but also for the health and conservation of infected species.”

In their review, the authors explain different scenarios for how transmission of human viruses might affect animals. On the other hand, it is conceivable that the transmitted virus leads to a large burden of disease and many deaths in infected animals – a major problem for species protection efforts. On the other hand, it is possible that the virus will find a new reservoir in animal species and may even form new and worrying variants. Whether or not it makes the animals visibly sick plays only a minor role. This scenario, in turn, poses a problem for human health: because even if the spread of such a virus in human society could be reduced, for example through increased hygiene and other public health measures, the pathogen could return from animals to transmitted humans – The so-called “secondary repercussions”.

Predictions thanks to artificial intelligence

Based on the literature evaluated in the current study, this risk exists but is not widespread. “Relatively few documented examples resulted in morbidity and mortality in animals, and few resulted in the retention of human pathogens in a new reservoir or subsequent ‘secondary repercussions’ in humans,” the researchers wrote. In order to prepare for future situations, it is important to be able to predict reasonable transfers and their possible effects. Artificial intelligence, which draws its conclusions on a solid research basis, can help here.

The first results in this area are promising. Based on published predictions about what kinds of animals can be infected with Sars-CoV-2, scientists have often been right rather than wrong. “It is gratifying to see the payoff of sequencing the animal’s genome and understanding their immune systems,” says Colin Carlson, Alberi’s colleague. “The pandemic has given scientists a chance to test some prediction tools, and it turns out we are better prepared than we thought.”

Wildlife health monitoring

However, for other diseases, it is important to generate more knowledge on which such predictions can be based. “We monitor Sars-CoV-2 more closely than any other virus in the world, so we can detect when a spill has occurred. In other cases, where we don’t have a lot of information to work with, it is very difficult to reliably assess the risks,” he said. Carlson says. Therefore, it is important to monitor the long-term health of wild animals, says Fagre. “By observing more closely, we can detect cross-species transmission events more quickly and act accordingly.”

Source: Anna Fagre (Colorado State University, USA) et al, Ecology Letters, doi: 10.1111/ele.14003

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