Reverse zoonoses: Humans are getting their pets sick

In a recent comprehensive review, experts have brought attention to a lesser-known but increasingly significant issue in public health: reverse zoonoses.

This phenomenon, where diseases are transmitted from humans to animals (particularly pets), is more common than previously thought.

The research raises concerns about the health of both domestic and wild animals, and the potential implications for human health.

Zoonotic diseases 

Historically, the focus has been on zoonoses, diseases that jump from animals to humans. However, Dr. Benjamin Anderson from the University of Florida says people should also pay attention to disease transmission in the opposite direction. 

Dr. Anderson notes that pets sharing close quarters with humans are at a heightened risk of contracting diseases from their owners. “We’re starting to see a lot of examples of reverse zoonosis. Pets are more susceptible than, maybe, we previously thought “

Cross-species transmission 

Reverse zoonoses occur when a pathogen in humans mutates and adapts to a new animal host. Dr. Anderson noted that differences in the biology of animals and humans usually make it difficult for infectious diseases to spread between species. 

“Typically, the viruses that I will have as a human are not going to fit into the receptors that a dog or cat has,” he explained.

On the other hand, viruses like influenza and coronaviruses are prime candidates for cross-species transmission due to their RNA-based genetic material, which is more prone to replication errors and subsequent mutations.

Pets at risk from reverse zoonoses

Dr. Anderson mentioned several diseases that have been transmitted from humans to their pets, including swine flu, human norovirus, dengue, COVID-19 and tuberculosis, as well as several lesser-known viral, fungal, parasitic and bacterial infections. 

Mammals, due to their genetic similarity to humans, are more susceptible to catching diseases from their owners. This includes pets like dogs, cats, horses, and ferrets. 

Disease reservoirs 

Reverse zoonoses not only affect household pets but also have wider implications. Livestock and wildlife can contribute to the spread of diseases – and to the risk of new outbreaks among humans. 

Dr. Anderson pointed out that domestic animals can become reservoirs for pathogens, potentially leading to pandemics.

Broader implications

“We have to first ask how the pathogen gets into those animals in the first place,” said Dr. Anderson. “The pathogen doesn’t develop out of thin air in animals before suddenly spilling over into humans.”

“While pathogens certainly can move from animals to other animals and can be picked up from the environment, exposures to humans also plays an important role. It’s this constant back and forth exchange that happens over time, increasing the probability of a mutation taking place that allows the pathogen to infect a new host.”

Dr. Anderson noted the difficulty in tracking reverse zoonoses, given the challenge in linking animal illnesses to human cases. This has led to a lack of attention towards this issue in both research and media.

Combating reverse zoonoses 

To combat reverse zoonoses, Dr. Anderson advises caution around pets, especially when the owner is sick with communicable diseases like the flu or COVID-19. He suggests limiting contact and maintaining hygiene to prevent transmission. 

Dr. Anderson also calls for more integrated research, combining human and animal health data, to better understand and manage these diseases.

“We have the diagnostic tools to track many different pathogens in both human and veterinary medicine, but not always the resources to see them used as broadly as is necessary to understand all of the epidemiological trends. In particular, we need greater testing among animals.”

“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.”

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