Taking a Bite Out of Disease:
How Bobcats Protect Us from Zoonoses

The global impact of the SARS-CoV-2 (COVID-19) pandemic serves as a stark reminder of the profound consequences a single zoonosis can unleash on our world, disrupting economic, political, and social stability. As we navigate a coexistence with COVID-19, the headlines continue to sound alarms about the relentless threats posed by zoonotic diseases, whether emerging, re-emerging, or expanding into new territories. From Lyme disease and babesiosis transmitted by ticks, to malaria, West Nile virus, and dengue carried by mosquitos, to hantavirus spread by rodents, we find ourselves reaching for insect repellent, stockpiling treatments for pets and livestock, and speed-dialing local exterminators. Amidst these concerns, unsung heroes quietly patrol our yards, green spaces, pastures, and beloved outdoor havens. Bobcats, stealthy disease-control specialists, silently stalk their cosmopolitan prey, curbing the prevalence and transmission of infectious diseases across diverse habitats. Providing a priceless service, they safeguard the interconnected communities of humans, domestic animals, and wildlife from the threat of zoonoses. These elusive and underappreciated public health allies? Bobcats!

 

Bobcats Boost Biodiversity's Disease Dilution Effect

So, how exactly do bobcats perform these human health and veterinary services for us, our companion and agricultural animals, and all of the wildlife in the landscapes we frequent? One way is through promoting biodiversity.  

By feeding at the top of the food chain, bobcats control herbivore (e.g., cottontail rabbits, woodchucks) and mesocarnivore (e.g., opossums, raccoons) populations. This top-down regulation of ecosystems can have cascading effects on trophic relationships that increase the overall biodiversity of the bobcat-influenced system, whether it’s a pristine wildland, a sprawling ranch, or a suburban backyard. In turn, increased species diversity can reduce zoonoses transmission and other infectious pathogens (bacteria, fungi, parasites, prions, and viruses) through the dilution effect..

As illustrated in the image below and further detailed in LoGiudice et al. (2003), Levi et al. (2016), and Keesing and Ostfeld (2021), the “dilution effect” is when a high diversity of poor-quality hosts for pathogens and/or vectors (such as ticks, rodents, and mosquitoes) dilutes the effectiveness of high-quality hosts to spread disease, thereby reducing the overall risk of disease transmission. Over time, infectious pathogens and vectors have developed dependencies on specific hosts, known as reservoir hosts, which provide optimal conditions for the pathogens to multiply and spread. Although, other animals in the ecosystem may also act as hosts, they are either unable to support significant pathogen amplification or are less effective in transmitting the disease.

Example of the dilution effect in Lyme disease transmission. Image adapted from Sanjana Kulkarni 2023. 

 Ultimately, a robust population of bobcats contributes to higher biodiversity, which, in turn, diminishes infectious pathogen transmission. This reduction in disease risk extends to humans, domestic animals, and wildlife within the ecosystem, highlighting the interconnectedness of a healthy bobcat population, increased biodiversity, and a lower risk of disease transmission. 

The most compelling evidence supporting the concept of biodiversity’s “dilution effect” is found in the dynamics of Lyme disease transmission - a tick-borne illness caused by Borrelia bacteria. In many parts of the United States, white-footed mice act as the primary hosts, amplifying these bacteria. Without bobcats and their biodiversity-enhancing influence, unchecked populations of white-footed mice become prime targets for ticks, loading them with Borrelia and increasing the likelihood of them infecting humans with Lyme-disease.

Introduce bobcats back into the ecosystem, and the scenario changes dramatically. Bobcats through predation, directly reduce the population of mouse reservoirs. Simultaneously, the rise in non-reservoir species draws ticks away from feeding on mice laden with bacteria. With a greater variety of potential hosts and a lower bacterial load, ticks are now less likely to feed on you, let alone infect you with Lyme disease.

A tangible illustration of this biodiversity-driven effect can be seen in a recent study by Lilly et al. (2022) in the San Francisco Bay Area of California. The research revealed that nymphal ticks in locations with diverse predator species, including bobcats, had the lowest infection rates with Lyme disease-causing bacteria. Furthermore, areas with higher predator abundance correlated with fewer ticks recovered from individual birds, providing additional evidence supporting the effectiveness of the dilution effect.

Bobcats Directly “Dilute” Diseases

Promoting biodiversity through the “dilution effect” is a crucial ecosystem service provided by bobcats to our human and animal communities. Yet, the bobcat’s contribution to controlling the spread of zoonoses and other infectious diseases goes beyond this. Bobcats actively diminish diseases in the environment in three additional ways:

1. Bobcats serve as inefficient hosts for various pathogens. When infectious agents invade a host, they must replicate successfully to reach numbers high enough to infect another host. Bobcats, as inefficient hosts, acts as “dead-end hosts” for several zoonotic diseases, including West Nile virus and Chagas disease. In such cases, the pathogens are blocked by the immune system or other physiological processes, breaking the disease transmission cycle.
2. Bobcats impede the spread of vector-borne diseases by reducing the number or efficiency of vectors. Vector-borne pathogens rely on vectors to move from host to host and continue the transmission cycle. Bobcats hinder the transmission of such diseases by consuming vectors, like kissing bugs that transmit the parasite that causes Chagas disease, and by altering the behavior of vectors’ hosts, such as the wildlife hosts of tick vectors. For example, Lilly et al. (2022) found that the presence of bobcats (and other predators) may frighten birds into spending more time in the trees, making potential hosts less accessible to tick vectors. If ticks cannot feed on birds, then the ticks cannot transfer Lyme-disease-causing bacteria to these potential hosts. You can thank bobcats for the healthy birds that visit your birdfeeders or fuel your bird-watching addiction.
3. Bobcats decrease the number or efficiency of reservoir hosts, which are critical for the replication and spread of infectious diseases. Here is where the bobcat shines: the diverse diet of these wild felids includes the primary reservoirs for some of the most devastating infectious diseases that plague humans, our animals, and wildlife. By preying on animals such as rabbits, hares, beavers, squirrels, and opossums, bobcats target reservoirs for diseases like tularemia and Equine Protozoal Myeloencephalitis. Their diverse diet helps control the circulation of infectious pathogens directly and indirectly transmitted by rodents, protecting humans, pets, livestock and wildlife from diseases such as hantavirus, leptospirosis, Lyme disease, and sylvatic plague.

As inefficient hosts and predators of key vectors and reservoirs for various infectious diseases, bobcats emerge as essential “disease dilutors” in the ecosystem.

Bobcats reduce disease risk by consuming prey that would otherwise spread disease. They are one of the few species that provide this public health service in areas with high levels of human activity. Photo credit: Karin Saucedo.

 

Disease control where you need it most

Few apex predators are as versatile as bobcats in supporting biodiversity’s “dilution effect” to mitigate disease risk. Thriving in diverse ecosystems, bobcats uniquely adapt to coexist in human-dominated landscapes, where their public health services are most crucial. The interface between wild areas and human frequented habitats, such as suburbs, open spaces, and agricultural lands, poses the highest risk for zoonotic disease spillover. In urban-scapes, the protective benefits of biodiversity and the “dilution effect” can dwindle. The key to bobcats’ role as disease dilutors lies in their remarkable ability to reduce the prevalence and transmission of zoonoses in the ecosystems shared by us, our companion animals, and agricultural livestock. From pristine wildlands to the heart of bustling cities, bobcats emerge as unwavering allies in our collective fight against infectious diseases, safeguarding our health wherever our paths intertwine.

Actions You Can Take to Reduce Disease Transmission

Contrary to sensationalized media reports on isolated cases of rabies in bobcats, these elusive creatures are not significant hosts or vectors for zoonotic diseases and rarely contract rabies. While they can carry Bartonella (linked to “cat scratch fever”) and Toxoplasma gondii like domestic cats, the transmission risk to humans is virtually nonexistent, with a far greater likelihood of exposure from pet or feral domestic cats than from wild bobcats. Similarly, bobcats are more prone to contracting diseases from domestic pets, such as canine distemper virus from dogs and various viruses from cats (i.e. feline calicivirus (FCV), feline panleukopenia virus (FPV), and feline immunodeficiency virus (FIV)), than the other way around. In terms of disease transmission, bobcats pose a greater risk to themselves from human and pet interactions.Supporting our feline disease control specialists involves coexisting with bobcats responsibly.

Supporting our feline disease control specialists involves coexisting with bobcats responsibly.

Here are additional tips to actively contribute to the well-being of bobcats and their disease-diluting public health service:

1. If you encounter a bobcat acting strangely (for example, circling or having difficulty walking), injured or ill, or possibly orphaned:
   - DO NOT touch or approach the animal.
   - Maintain a safe distance, keeping others away as well
   - Promptly contact a wildlife rescue organization. Use resources like Animal Help Now for wildlife emergencies.
2. Refrain from using anticoagulant rodenticides, as they were prohibited in California in 2020 due to their harmful impact on wildlife. Opt for alternatives like rat fertility control baits or habitat management. Anticoagulant rodenticides not only poison rodents, but also pose a severe threat to bobcats through secondary poisoning, affecting their immune system and increasing susceptibility to diseases like mange. Counterintuitively, using anticoagulant rodenticides may actually increase rodent infestations by removing bobcats and other natural predators of rodents via this type of secondary poisoning.
3. Ensure companion and agricultural animals are up-to-date on vaccinations and follow veterinarian-recommended de-worming practices.
4. Keep domestic cats indoors or leashed when outside to ensure their safety, health, and longevity.
5. Avoid allowing dogs to free-range and always keep them on a leash when off your property to prevent encounters with other animals and minimize disease-transmitting behaviors. You should also pick up after your dog when they defecate.
6. If you live in areas with frequent wildlife sightings, inspect your yard for bobcats and other wildlife before letting pets outside. Regularly clean up pet waste using gloves and dispose of it properly in sealed plastic bags in the trash.

By following these guidelines, we actively contribute to the wellbeing of bobcats and foster a healthy coexistence that benefits both wildlife and domestic animals.

References

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Riley, S. P. et al. (2004). Exposure to feline and canine pathogens in bobcats and gray foxes in urban and rural zones of a national park in California. Journal of wildlife diseases, 40: 11-22.

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