Reverse zoonoses are more common than once thought.

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Dr. Anderson’s current work uses novel sampling technologies such as bioaerosols to detect emerging viruses in infectious disease hotspots and vulnerable populations with high contact with animal reservoirs. Credit: University of Florida

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Dr. Anderson’s current work uses novel sampling technologies such as bioaerosols to detect emerging viruses in infectious disease hotspots and vulnerable populations with high contact with animal reservoirs. Credit: University of Florida

For as long as humans have domesticated animals, there have been zoonoses, also known as infectious diseases that jump from animals to humans. Recent public health stories about COVID-19, avian flu and swine flu have brought zoonoses back into the spotlight, sparking discussions about whether pets, rodents, birds or livestock How can people get sick?

But people should also pay attention to transmission of the disease in the opposite direction, said Benjamin Anderson, Ph.D., assistant professor at the University of Florida’s College of Public Health and Health Professions and a member of the Emerging Pathogens Institute. Anderson is also a member of the UF One Health Center of Excellence.

In June 2023, he and his colleagues published A comprehensive review Studies documenting instances of reverse zoonosis, or human being– From the animal Disease transmissionIncludes viral, bacterial, fungal and parasitic pathogens. In the paper Zoonoses: Infections affecting humans and animals warned that pets, who share beds, kisses, cuddles and food with humans, are at risk of catching diseases from their owners.

“We’re starting to see a lot of examples of reverse zoonosis. Pets are more susceptible than we might have previously thought,” Anderson said.

What are reverse zoonoses?

Differences in the biology of Animals And humans usually make it difficult for him. Infectious disease to spread between species. For example, a virus must bind to specific cell receptors in the host in order to reproduce and continue its life cycle.

“Typically, viruses that I would have as a human wouldn’t fit into the receptors that a dog or a cat would have,” Anderson explained.

Due to Genetic diversity As may be the case in a viral population, there will be different strains with different levels of success in fighting off the host’s immune system and entering the host’s cells. Varieties that can reproduce more will become more common over time.

There is also a possibility. The virus Creating a mutation that coincidentally allows it to fit into a new receptor and cross the species barrier. The risk of this happening increases every time the virus is transmitted and replicates in the presence of both humans and animals, especially when pets leave the home. It’s important to minimize transmission, Anderson said, because each individual infection increases the chance of mutation, and a new viral strain emerges.

Yet, reverse zoonosis receives little attention from researchers and the popular media. This is partly because it’s much easier to track incidents where pets make their owners sick instead.

“When you see a person in a clinic, you can ask questions like, was they around an animal, or did they have a pet that was sick. But when you get an animal that’s sick happens, so you might not always be able to experience that kind of information to link it back to the human case,” Anderson said.

What types of reverse zonos already exist?

But just because people aren’t paying attention to reverse zoonosis doesn’t mean it isn’t happening. The biggest impact comes from influenza and coronaviruses, which are amenable to mutation because their genetic material is stored in RNA, essentially a stranded version of DNA. The enzyme is not as good at checking for errors in RNA replication as DNA proofreading enzymes—as a result, RNA viruses have higher error rates and more frequent mutations. This is why there are so many influenza and coronavirus strains. This also makes these viruses potential candidates for transmitting diseases across species.

Anderson’s paper describes several diseases that are transmitted from humans to their pets, including Swine fluhuman norovirus, dengue, COVID-19 and tuberculosis, as well as many lesser-known viral, fungal, parasitic and bacterial infections. While the majority of cases involved dogs and cats, some transmissions between horses, ferrets, and parrots were also documented.

Not all pets face the same risk of reverse zoonosis. Mammals are more likely than birds or reptiles to get sick from their owners because they share more genetic similarities with humans. This means that viruses do not have to mutate as much to cross the species barrier. Receptors in animal cells are sometimes determined by whether the animal is a mammalian, reptilian, or avian species. For example, the ACE2 receptor, which is responsible for the virus that causes COVID-19, is present in all mammals with minor variations.

What are the effects of reverse zoonoses?

In addition to being a health risk to beloved pets, reverse zoonoses can later affect humans by contributing to the spread of disease. Most seasonal flu viruses bind to a cell receptor found in humans and pigs, and in birds in a slightly different configuration. This unique biological situation allows pigs to be infected with both human and avian influenza viruses at the same time. When this happens, pigs can sometimes act as mixing reservoirs and produce new viruses that can cause epidemics.

Domestic animals such as pigs can also maintain pathogen populations and become growing reservoirs. In 2016, Anderson co-authored a paper studying the spread of influenza virus among people working in the swine industry. During the 2009 to 2010 and 2010 to 2011 flu seasons, when the 2009 pandemic influenza virus was circulating, cases peaked in counties with high hog production. The researchers believe that the flu virus was circulating within the pigs, creating a way for it to spread to the human population.

“We have to first ask how the pathogen gets into these animals in the first place,” Anderson said. “Pathogens do not appear out of thin air in animals before they suddenly spread to humans. While pathogens can certainly be transmitted from animal to animal and picked up in the environment, exposure to humans is also an important plays a role. The constant back-and-forth exchange that occurs over time increases the likelihood of a mutation occurring that allows the pathogen to infect a new host.”

Detection of zoonotic transmission can be difficult because pathogens do not always cause symptoms upon infection, and diagnostic testing is often limited even in symptomatic cases. This means that disease movement between species can occur without anyone realizing it. But regardless of whether an animal is sick, as long as it has the pathogen, it increases the overall movement of the disease in the environment—putting the health of other organisms at risk.

What can we do to fight reverse zoonosis?

To help control zoonotic and reverse zoonotic transmission, Anderson recommends that people who are sick be extra careful around their pets, especially if they know they have COVID or the flu. This does not mean complete quarantine, as separation from their companion animals is not always possible or preferred.

Strong human-animal bonds also come with many benefits for emotional and mental well-being that should not be discounted. Owners can make a meaningful difference by restricting pets and keeping bodily fluids away from pets when they are sick, Anderson said. On a day-to-day basis, people can also limit the spread of disease by feeding pets healthy food, providing fresh drinking water, maintaining a clean living area and following the recommended vaccination schedule.

At the systemic level, more integrated research can also reduce the effects of reverse zoonoses. This means not only focusing on human health data but also incorporating animal surveillance to understand a disease. “We have diagnostic tools that can track many different pathogens both in humans and in humans. Medicines for livestock, but these resources are not always used as widely as necessary to understand all epidemiological trends. In particular, we need more testing in animals,” Anderson said. This type of data can support pandemic preparedness by giving scientists important information about the movement of pathogens.

“I think it’s important not only to learn about human health issues, but also to get a more complete picture of what’s actually going on in the environment,” Anderson said.

More information:
Benjamin D. Anderson et al, Reverse Zoonotic Transmission (Zooanthroponosis): A Growing Threat to Animal Health, Zoonoses: Infections affecting humans and animals (2023). DOI: 10.1007/978-3-030-85877-3_59-1

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