If animals can get sick, just saving humans won’t stop the pandemic

In this file photo from Friday, Nov. 6, 2020, minks are seen exiting an enclosure at a farm near Nystved, Denmark. Danish Prime Minister Mette Frederiksen appointed a new agriculture minister on Thursday, Nov. 19, 2020. Earlier, Mogens Jensen resigned after the government had ordered the killing of all Danish minks due to the coronavirus, but the necessary legislation was not enacted. | Photo credit: AP

When the World Health Organization COVID-19 declared a pandemic As of March 11, 2020, humans were the only species in which cases of the disease had been reported. While initial genetic analyses indicated Horseshoe bats As the evolutionary host of SARS-CoV-2, the virus that causes COVID-19, there have been no reports to date indicating that it can spread from humans to other animal species.

Less than two weeks later, a report from Belgium indicated that First infection in a domestic cat – possibly by its owner. News of the COVID-19 outbreak and its aftermath occurred in the summer of 2020 Slaughter in the Mink Farm Similar calls expected across Europe Slaughter in North AmericaHumans and other animals on and around mink farms have tested positive, raising questions about the possibility of a secondary wildlife reservoir of COVID-19. That is, the virus could infect and establish an infection cycle in a species other than the one in which it originated.

Researchers have documented this phenomenon of human-to-animal transmission, colloquially referred to as ‘human-to-animal’ transmission. Spillback or reverse zoonotic transmissionin both domestic and wild animals. Wildlife can become infected either directly from humans or indirectly from domesticated animals infected by humans. This stepping-stone effect provides new opportunities for pathogens to evolve and can radically change the way they spread, as seen in Influenza And Tuberculosis,

For example, spillback has long been a threat. Endangered great apesEven in populations where human contact is minimal, the chimpanzees at Gombe National Park, made famous by the work of Jane Goodall, have suffered outbreaks of measles and other respiratory diseases that are likely caused by this. persistence of pathogens in the environment Spread by people living nearby or ecotourists.

We are researchers who study Mechanisms driving inter-species disease transmission How else Disease affects both wildlife conservation and peopleEmerging outbreaks have underscored the importance of understanding how threats to wildlife health shape the emergence and spread of zoonotic pathogens. Our research suggests that looking at historical outbreaks could help predict and prevent the next pandemic.

Spillback has happened before

Our research group wanted to assess how frequently spillbacks were reported in the years before the COVID-19 pandemic. Retrospective analysis not only helps us identify specific trends or barriers to reporting spillback events, but also helps us understand where new emerging threats are most likely.

We examined historical spillback events involving different groups of pathogens in the animal kingdom, taking into account variations in geography, methods and sample sizes. Synthesized Scientific Reports of Spillback During the nearly century before the COVID-19 pandemic — from the 1920s to 2019 — diseases ranging from salmonella and intestinal parasites to human tuberculosis, influenza and polio were prevalent.

We were also interested in whether bias in detection and reporting might affect what is known about human-to-animal pathogen transmission. Charismatic Megafauna – often defined as large mammals such as pandas, gorillas, elephants, and whales that evoke emotions in people – is overrepresented in wildlife epidemiology and conservation efforts. They receive more public attention and funding than smaller and less visible species.

Difficulties are making it even more complicated Monitoring wild populations of small animalsBecause they decay quickly and are often eaten by larger animals, this drastically reduces the period of time during which researchers can investigate outbreaks and collect samples.

The results of our historical analysis support our suspicion that most of the reports describe Outbreaks in large charismatic megafaunaMany of these were captive, such as in zoos or rehabilitation centers, or semi-captive, such as the well-studied great apes.

Despite the long list of published papers on new pathogens found in bats and rodents, the number of studies examining pathogens transmitted from humans to these animals was very low. However, small mammals occupy a variety of ecological niches, including those living near human habitations – e.g. Deer mice, Rats and skunks – They are not only more likely to share their germs with people, but are also more likely to become infected with human germs.

COVID-19 and Pandemic Flu

In our historical analysis of spillback before the COVID-19 pandemic, the only evidence we found supporting establishment of a human pathogen in wildlife populations were two reports from 2019 that described H1N1 infection in striped skunksLike coronaviruses, influenza A viruses such as H1N1 are adept at switching hosts and can infect a wide range of species.

However, unlike the coronavirus, these tend to spread widely. Facilitated by migratory waterbirds How these skunks became infected with H1N1 and for how long they remained infected is not yet clear.

Shortly after the analysis of our study was completed, reports indicated that Widespread COVID-19 infection in white-tailed deer Cases of infection began to be reported across North America in November 2021. Prevalence of infection in some areas Up to 80% In spite of this little evidence of disease In the deer.

This ubiquitous mammal has effectively become the secondary reservoir of COVID-19 in North America. Furthermore, genetic evidence suggests that SARS-CoV-2 White-tailed deer grow three times faster There is already evidence that new variants are more contagious than those in humans, potentially increasing the risk of spreading to humans and other animals. Transmission from deer to humans A variant of Covid-19 that had never been seen before.

there are There are over 30 million white-tailed deer in North AmericaMany are in agricultural and suburban areas. Surveillance efforts to monitor viral evolution in white-tailed deer can help identify emerging variants and identify further transmissions from deer populations to people or pets.

Research on related species has shown that the risk of spillback varies. For example, White-tailed deer and mule deer In the lab, elk are highly susceptible to COVID-19, while moose are not.

H5N1 and US dairy herds

Since 2022, the spread of H5N1 has affected Wide range of birds and mammalian species around the world – foxes, skunks, raccoons, opossums, polar bears, coyotes and seals, to name a few. Some of these populations are threatened or endangered, and aggressive surveillance efforts are underway to monitor viral spread.

Its presence was reported by the US Department of Agriculture earlier this year. H5N1 in the milk of dairy cowsGenetic analysis has shown that the virus has also entered cows. By December 2023possibly in the Texas Panhandle. Since then, it has 178 livestock herds in 13 states By August 2024.

It is not yet known how the virus spread to dairy cows, but this is probably how it happened. Migratory waterfowl infected with virus. Efforts are underway to determine how the virus spreads between herds, although it appears contaminated milking equipment Instead of Aerosol transmissioncould be the culprit.

Given the ability of influenza A viruses such as avian flu to infect multiple species, it is critical that surveillance efforts target not only dairy cows but also animals living on or near affected farms. Monitoring high-risk areas for cross-species infection, such as where livestock, wildlife and people interact, not only provides information about how widespread a disease is in a given population – in this case, dairy cows – but also allows researchers to identify susceptible species they come into contact with.

To date, H5N1 has been detected in several animals found dead on affected dairy farms, including: Cats, birds and a raccoonBy August 2024, four people Ten people who came into close contact with infected dairy cows have tested positive, including one develop respiratory symptomsOther wildlife and domestic animal species are still at risk. Monitoring Efforts Work is ongoing to monitor H5N1 transmission from poultry to humans.

Humans are only part of the network

The language often used to describe cross-species infection fails to encompass its complexity and nuance. Given the number of species that have been infected with COVID-19 during the pandemic, many scientists have said that cross-species transmission should serve as an effective measure to prevent the spread of the disease. Limiting the use of the terms spillover and spillback Because they describe the transmission of pathogens from humans and to humans. This shows that disease and its consequences start with humans and end with humans.

Treating humans as one node in a larger network of infection possibilities can help researchers monitor COVID-19, H5N1 and other emerging zoonoses more effectively. This includes systems-thinking Approaches such as One Health or Planet Health capture it Human interdependence with the health of the overall environment.

This article is republished from The Conversation under a Creative Commons license. Original article,