Throughout the history of humans domesticating animals, there has been a concern about zoonoses—diseases that can transfer from animals to humans. Recent health stories, such as those about COVID-19, avian flu, and swine flu, have brought attention back to zoonoses, sparking discussions about the potential health risks associated with pets, rodents, birds, or livestock. However, Benjamin Anderson, Ph.D., an assistant professor at the University of Florida's College of Public Health and Health Professions and a member of the Emerging Pathogens Institute, suggests that we should also consider the transmission of diseases in the opposite direction—from humans to animals.
Anderson, who is also a member of the UF One Health Center of Excellence, and his colleagues conducted a comprehensive review of studies on reverse zoonosis. This involves diseases passing from humans to animals, encompassing viral, bacterial, fungal, and parasitic pathogens. The study, published in Zoonoses: Infections Affecting Humans and Animals in June 2023, particularly emphasized the risk posed to pets, which often share close contact with humans.
"We're starting to see a lot of examples of reverse zoonosis. Pets are more susceptible than, maybe, we previously thought," noted Anderson.
Reverse zoonoses occur when infectious diseases face difficulties spreading between different species due to differences in their biology. Viruses, for instance, must bind to specific cell receptors in the host to replicate. Anderson explains that the genetic diversity of a viral population may lead to mutations allowing it to cross species barriers. The risk of this happening increases when viruses are transmitted between humans and animals, making homes with pets vulnerable.
Despite the significance of reverse zoonosis, it receives less attention compared to instances where pets transmit diseases to their owners. Anderson attributes this to the challenge of obtaining information when animals fall ill. However, he stresses that it's crucial to address this issue, especially considering the potential impacts on both animal and human health.
The study identified several diseases transmitted from humans to pets, including swine flu, human norovirus, dengue, COVID-19, and tuberculosis. While most cases involved dogs and cats, other animals like horses, ferrets, and parrots were also affected. Mammals, with their genetic similarities to humans, are more likely to be susceptible to reverse zoonosis than birds or reptiles.
The impacts of reverse zoonoses extend beyond pets, potentially contributing to the spread of diseases among humans. Influenza and coronaviruses, known for their high mutation rates, pose a significant risk. Pigs, for example, can become reservoirs for new viruses, leading to the emergence of pandemic strains.
To address reverse zoonoses, Anderson recommends that individuals who are sick take precautions around their pets, even if a complete quarantine is not feasible. Maintaining a healthy living environment for pets, providing proper nutrition, fresh water, and following vaccination schedules can also minimize the risk of disease transmission. On a broader scale, integrated research that includes both human and veterinary data is essential for understanding epidemiological trends and enhancing pandemic preparedness.
"I think it's important to know not just about the human health issues but also have a more complete picture as to what's actually happening out in the environment," Anderson emphasized.