Pets are often considered as part of the family, providing us with companionship, comfort, and joy. But they can also pose a serious health threat that we have overlooked, according to a new study. The study warns that backyard pets, working animals, and urban pests can be sources of zoonotic microbes that jump from animals to humans, especially in the context of increasing urbanization and climate change.

Zoonotic spillover from companion animals and strays

Zoonotic spillover is the term used to describe the transmission of an infection from animals to humans. It does not necessarily mean that the infection will cause a pandemic or even an epidemic, but any infection that crosses the species barrier is classified as zoonotic. The COVID-19 pandemic has highlighted the importance of monitoring and preventing zoonotic spillover from exotic animals and wildlife trade, but the study suggests that we should also pay attention to the risk posed by our domesticated and feral animals.

How Pets Can Put Our Health at Risk by Spreading Zoonotic Diseases
How Pets Can Put Our Health at Risk by Spreading Zoonotic Diseases

The study, published in Science Translational Medicine, was conducted by disease ecologist Amandine Gamble and colleagues from the University of California, Los Angeles. They reviewed the literature on zoonotic diseases associated with companion animals and strays, and found that these animals can play critical roles in zoonotic spillover by maintaining, spreading, bridging, or evolving zoonotic pathogens.

The study authors argue that this risk is underestimated, and although it is small and limited to rare events, it is nevertheless a real threat to health due to the proximity of pets and strays to people. They also point out that the dynamics of zoonotic spillover from these animals are likely to change as urbanization and climate change alter the interactions between humans, animals, and the environment.

Examples of zoonotic diseases from pets and strays

The study provides several examples of zoonotic diseases that can be transmitted from pets and strays to humans, some of which may surprise you. For instance, did you know that cats can act as a link in the chain of infections of Yersinia pestis, the bacterium that causes plague? Plague is historically associated with rats and their fleas, but cats can also catch it from their prey or other infected cats. Cats can then transmit it to humans through bites, scratches, or contact with their saliva or blood.

Plague is endemic in 17 western US states, where many of the small mammals that cats prey on carry Y. pestis. The study authors warn that outdoor cats and cats with incomplete veterinary care, combined with human interaction, suggest that cat-transmitted plague can be considered an increasing public health risk.

Another example is rabies, a viral disease that affects the nervous system and can be fatal if not treated promptly. Rabies is usually transmitted by the bite of an infected animal, such as a dog or a bat. However, cats can also carry rabies and infect humans. In fact, according to the Centers for Disease Control and Prevention (CDC), more than 60 percent of all animal rabies cases reported in the US in 2019 were in cats.

The study authors note that free-roaming and feral cats are more likely to encounter rabid wildlife than indoor cats, and may not receive regular vaccination or veterinary care. They also mention that some people may feed or interact with stray cats without knowing their rabies status, increasing the risk of exposure.

Other zoonotic diseases that can be transmitted from pets and strays to humans include leptospirosis, toxoplasmosis, cat scratch disease, ringworm, salmonellosis, chlamydiosis, and more. Some of these diseases can cause mild symptoms such as fever, diarrhea, or skin rash, while others can lead to serious complications such as meningitis, blindness, or organ failure.

How to prevent zoonotic spillover from pets and strays

The study authors emphasize that they do not intend to discourage pet ownership or animal welfare efforts, but rather to raise awareness of the potential health risks and how to mitigate them. They suggest some strategies to prevent zoonotic spillover from pets and strays, such as:

  • Keeping pets indoors or limiting their outdoor access
  • Providing regular veterinary care and vaccination for pets
  • Avoiding contact with sick or injured animals
  • Washing hands after handling animals or their waste
  • Wearing gloves and protective clothing when cleaning animal habitats
  • Educating pet owners and animal caretakers about zoonotic diseases
  • Implementing population control measures for stray animals
  • Enhancing surveillance and reporting systems for zoonotic diseases
  • Conducting more research on the ecology and evolution of zoonotic pathogens

The study authors conclude that pets pose a serious health threat that we have overlooked, but also an opportunity to improve our understanding and prevention of zoonotic spillover. They call for more collaboration and communication among veterinarians, physicians, ecologists, and public health officials to address this emerging challenge.


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