Intersection of Human and Wildlife Health at the Urban Edge - disease and zoonoses, spillover threats and questions for research today

COVID-19 swept the world, and brought attention to the rising threat of zoonoses, or diseases spread from animals to humans. With over 6.9 million people dead since 2020, COVID-19 is just one example of the many zoonoses that have impacted the human population in recent years(1). Other well-known examples include Ebola, Zika virus, bird flu, swine flu, and smallpox.

Infectious diseases are appearing at an unprecedented rate, largely due to increased travel, greater human population density, and increasing rates of contact with wildlife(2). Zoonoses constitute a major portion (60.3%), of emerging infectious diseases(3). Spillover, the event when a pathogen crosses over from a primary host disease to a new species, can occur in many different settings. There are many barriers to spillover occurring, as the pathogen must be able to adapt to the body of the new host(4). Increased contact with disease host populations increases the chance of spillover events. Land use change and habitat destruction force more and more wildlife to move into developed areas(5), increasing human and wildlife contact. 71.8% of zoonotic EID’s originate in wildlife(3).

What does this mean for the relationship between humans and wild cats? Proximity between species creates more chances for pathogens to jump from cats to humans(6,7), as humans are increasingly likely to share spaces with wild felids(8). However, there is another indirect pathway that also poses a threat. In many parts of the world, domestic cats and wild cats live in close proximity.

As wild cats are pushed to the urban edge, they are forced to live in close quarters with domestic cats, creating opportunities for diseases to cross over between populations(9). For example, domestic and wild cats living on and around palm oil plantations in Malaysian Borneo were found to share many of the same diseases(10). From there, close proximity of people to house cats creates a viable pathway for pathogens to leap from wild cat populations to humans. Wild cats can carry diseases that are already known to infect humans, such as plague(11), hookworm, and toxoplasmosis(12). Similarly, COVID-19 was found to infect tigers, lions, snow leopards, pumas, and domestic cats(13). As the daily paths of humans and wild cats are forced to intersect more and more, the risk of disease crossover between people and wild felids increases.

There are several actions that can be taken to protect the safety of both humans and the wild cat population (and that of domestic cats). First and foremost, keeping domestic cats indoors greatly decreases the chance of them becoming infected with pathogens from wild cats. In turn, this means they are less likely to introduce those pathogens to people. Wild cats are also known to prey upon domestic cats, exposing wild cats to numerous diseases that cause significant harm to their populations14. Reducing interactions between domestic and wild cats will reduce the chance of disease transmission between the two.

Another important component of reducing the spread of zoonotic diseases is supporting habitat restoration. Restoring landscapes to healthy ecosystems creates safe pathways between habitat patches, giving wild cats more safe places to roam, and reducing the pressure on them to adapt to urban landscapes.

The most important factor, however, is not just restoring damaged habitats, but preventing their loss. There are numerous pathways to this: urban planning that supports human density rather than sprawl(15), governmental support of regenerative agriculture and clean energy, controlling and combatting spread of invasive species(16), among others. It is essential to prioritize the minimization of habitat loss because research shows that full landscape restoration is a difficult process. Landscapes caught in transition are generally not as effective at preventing the spillover of zoonotic diseases, when compared to mature, healthy landscapes(17). Careful measures and thoughtful restoration methods can return a landscape to a healthy state, but prevention is the most effective strategy.

Further research to explore the potential for zoonotic diseases originating in wild cats is needed, as well as studies on the effects of landscape restoration on disease spillover. While wild felids are not a major source of zoonotic disease for humans, there are still pathways for pathogens to cross between human and wild cat populations. Increasing human encroachment and disturbance in and around wildlife habitat, increases that proximity between those groups and thus, the risk of disease transmission. For the wellbeing of both cats and humans, greater measures must be taken to preserve and restore habitats and ecosystems, as human wellbeing is linked to the preservation of nature(18).

References

(1)World Health Organization (WHO). (2023). WHO Coronavirus (COVID-19) Dashboard.https://covid19.who.int/

(2)Baylor College of Medicine. (2023). Emerging Infectious Diseases.https://www.bcm.edu/departments/molecular-virology-and-microbiology/emerging-infect ions-and-biodefense/emerging-infectious-diseases

(3)Jones, K. E., Patel, N. G., Levy, M. A., Storeygard, A., Balk, D., Gittleman, J. L., & Daszak, P.(2008). Global trends in emerging infectious diseases. Nature, 451: 990–993.  

(4)Ryding, Sara. (2021). What is a Spillover Event? News-Medical. https://www.news-medical.net/health/What-is-a-Spillover-Event.aspx.

(5)Benson, J.F., Sikich, J.A. and Riley, S.P. (2016). Individual and population level resource selection patterns of mountain lions preying on mule deer along an urban-wildland gradient. PLoS One, 11: e0158006.

(6)Gerhold, R.W. and Jessup, D.A. (2013). Zoonotic diseases associated with free‐roaming cats. Zoonoses and public health, 60: 189-195.

(7)Taetzsch, S.J., Bertke, A.S. and Gruszynski, K.R. (2018). Zoonotic disease transmission associated with feral cats in a metropolitan area: A geospatial analysis. Zoonoses and public health, 65: 412-419.

(8)Stoner, D.C., McDonald, Z. and Coon, C.A. (2023). Stepping stones to extirpation: Puma patch occupancy thresholds in an urban‐wildland matrix. Ecology and Evolution, 13: e10381.

(9)Bevins SN, Carver S, Boydston EE, Lyren LM, Alldredge M, Logan KA, et al. (2012) Three Pathogens in Sympatric Populations of Pumas, Bobcats, and Domestic Cats: Implications for Infectious Disease Transmission. PLoS ONE 7(2): e31403.  

(10)Guerrero‐Sánchez, S., Wilson, A., González‐Abarzúa, M., Kunde, M., Goossens, B., Sipangkui, R., & Frias, L. (2022). Serological evidence of exposure of Bornean wild carnivores to feline‐related viruses at the domestic animal–wildlife interface. Transboundary andEmerging Diseases, 69. 

(11)Elbroch, L., Vickers, T., & Quigley, H. (2020). Plague, pumas and potential zoonotic exposure in the Greater Yellowstone Ecosystem. Environmental Conservation, 47:75-78. 

(12)Meireles, L.R., Galisteo Jr, A.J., Pompeu, E. and Andrade Jr, H.F. (2004). Toxoplasma gondii spreading in an urban area evaluated by seroprevalence in free‐living cats and dogs. Tropical medicine & international health, 9: 876-881.

(13)Giraldo-Ramirez, S., Rendon-Marin, S., Jaimes, J. A., Martinez-Gutierrez, M., & Ruiz-Saenz, J. (2021). SARS-CoV-2 Clinical Outcome in Domestic and Wild Cats: A Systematic Review. Animals, 11: 2056. 

(14)Florida Fish and Wildlife Conservation Commission. (2023). Panther Health.https://myfwc.com/wildlifehabitats/wildlife/panther/health/

(15)McDonald, R.I., Aronson, M.F., Beatley, T., Beller, E., Bazo, M., Grossinger, R., Jessup, K., Mansur, A.V., Puppim de Oliveira, J.A., Panlasigui, S. and Burg, J. (2023). Denser and greener cities: Green interventions to achieve both urban density and nature. People and Nature, 5: 84-102.

(16)Weidlich, E.W., Flórido, F.G., Sorrini, T.B. and Brancalion, P.H. (2020). Controlling invasive plant species in ecological restoration: A global review. Journal of Applied Ecology, 57: 1806-1817.

(17)Vinson, J. E., Gottdenker, N. L., Chaves, L. F., Kaul, R. B., Kramer, A. M., Drake, J. M., & Hall,R. J. (2022). Land reversion and zoonotic spillover risk. Royal Society open science,9: 220582. https://doi.org/10.1098/rsos.220582.

(18)Sandifer, P.A., Sutton-Grier, A.E. and Ward, B.P. (2015). Exploring connections among nature, biodiversity, ecosystem services, and human health and well-being: Opportunities to enhance health and biodiversity conservation. Ecosystem services, 12: 1-15.