Cats: Why They Should be Enclosed and Not Roam Free


By Michael W. Fox BVetMed, PhD, DSc, MRCVS

Presented to Minneapolis Animal Care and Control, August 12th 2021

I love cats as well as all creatures wild and domesticated and am very opposed to allowing them to roam free. There is an estimated 24.5 million owned cats in the U.S. ( Source: 2017-2018 U.S. Pet Ownership & Demographics Sourcebook ). Unfortunately, there are no rigorous estimates for the number of feral cats living in the United States. The best available estimate suggests that the population is probably about 32 million, roughly 76% of whom live in urban areas. (Source: If half of America’s cat owners let their cats outdoors, this means there are around 44 million cats roaming free, at risk and putting wildlife and public health also at risk.

WIDLIFE CONCERNS: Free-ranging domestic cats kill an estimated 1.3–4.0 billion birds and 6.3–22.3 billion mammals annually. (Source: Cats compete with indigenous wild carnivores, including raptors, for prey and can spread diseases to them and bring home diseases from them as well as from the prey they consume. Millions of cats live in two worlds as indoor-outdoor animals (still a cultural norm in the U.K. and many other countries) and often bring home wild animals they have killed or injured such as chipmunks, voles, baby rabbits, chickadees and lizards, require veterinary treatments themselves for injuries and diseases as well as their owners who contract various infections and confront infestations that these cats bring back into their homes and beds. (For more details see the review article Also, for the humane alternative of TNE ( trap-neuter-enclose) to TNR ( trap-neuter-release) visit


Insectivorous birds like Barn Swallows, Swifts, Nighthawks, Purple martins, Eastern kingbirds, Sparrows, various migratory songbirds especially Warblers, like Blackpoll and Yellow warblers, Bluebirds. Eastern phoebes. House wrens. Hummingbirds, Baltimore Orioles and Red-eyed vireos are known for eating flying insects, including mosquitos. Many of these birds fall prey to free-roaming cats who, in turn, by reducing this natural mosquito control by birds, put humans and other animals at risk from mosquito-borne diseases. These include heart-worm disease (dirofilariasis) which is increasing in dogs, cats and humans. According to The United State Centers for Disease Control and Prevention (CDC) mosquitoes kill more than one million people a year just from the transmission of malaria. Scientists are concerned global warming could lead to the explosive growth of mosquito-borne diseases worldwide, some of the most common diseases spread by mosquito bites include Zika virus, West Nile virus, chikungunya virus and dengue fever, There is no vaccine to prevent or medicine to treat most of these diseases. So one prevention is to keep cats indoors or suitably enclosed to protect insectivorous birds.

Most municipalities in the U.S. use sprays to kill adult mosquitoes and pellets of insecticides spread often by helicopters over lakes to kill mosquito larvae. But in the process, they kill beneficial aquatic insects and other aquatic species that would consume the mosquito larvae while insectivorous reptiles, amphibians, bats and birds starve to death because their main food source of mosquitoes and other beneficial insects This loss of biodiversity, exacerbated by herbicides and insecticides used in agriculture, forestry and by gardeners, leads to dysbiosis and the proliferation of disease-transmitting chemical-resistant insects, notably sandflies, ticks and midges as well as various mosquito species.


In their review article “Rabies Prevention and Management of Cats in the Context of Trap, Neuter, Vaccinate, Release Programs”, veterinarians and scientists Allison D. Roebling, MPH, DVM, Dana Johnson, DVM, Jesse D. Blanton, MPH, Michael Levin, PhD, Dennis Slate, PhD, George Fenwick, PhD ,and Charles E. Rupprecht PhD summarize their findings as follows::

“Domestic cats are an important part of many Americans’ lives, but effective control of the 60–100 million feral cats living throughout the country remains problematic. Although Trap-Neuter-Vaccinate-Return (TNVR) programs are growing in popularity as alternatives to euthanizing feral cats, their ability to adequately address disease threats and population growth within managed cat colonies is dubious. Rabies transmission via feral cats is a particular concern as demonstrated by the significant proportion of rabies postexposure prophylaxis associated with exposures involving cats. Moreover, TNVR has not been shown to reliably reduce feral cat colony populations because of low implementation rates, inconsistent maintenance, and immigration of unsterilized cats into colonies. For these reasons, TNVR programs are not effective methods for reducing public health concerns or for controlling feral cat populations. Instead, responsible pet ownership, universal rabies vaccination of pets, and removal of strays remain integral components to control rabies and other diseases.” (Citation from Zoonoses Public Health. 2014 Jun; 61(4): 290–296. Published online 2013 Jul 17. doi: 10.1111/zph.12070)

Few municipalities have any effective ordinances mandating keeping cats indoors or enclosed on private property, creating a perfect storm, now exacerbated by climate change in many areas with increased rainfall and humidity and mosquitoes becoming insecticide-resistant. Thus a perfect storm is created for the spread of mosquito-borne diseases in communities that can sicken and kill people, companion animals, livestock and wildlife. NOTE: Two people in Delaware tested positive in Oct. 2021 for West Nile virus, and an unvaccinated horse with WNV was euthanized Oct. 5 after the animal became unable to stand. Both West Nile virus and Eastern equine encephalitis can be fatal to equids, and owners should “work with their veterinarian to set up a routine vaccination protocol,” said Deputy State Veterinarian Karen Lopez .Full Story: WBOC-TV (Salisbury, Md.) (10/8/21)

IN-FIELD STUDY OF PREDATION BY HOUSE CATS Researchers distributed GPS tracking backpacks to pet owners in six countries, including the United States, United Kingdom, Australia, and New Zealand. They collected data on both how far 925 pet cats roamed and how many animals they hunted down. Pet cats kill between two and ten times more wildlife than native predators, the researchers found.

“Our research shows that pet cats can have a large impact on prey populations, but that this is mostly localized near their houses,” said Roland Keys, lead author and a professor at North Carolina State University, in a video accompanying the study. Paired with the fact that house cats tend to live in close quarters with one another, our pets’ collective killing power can be four to 10 times greater than that of wild animals. All of this evidence adds up to one, straightforward solution to protect wildlife populations, Kays says: Keep your cat inside.

R.Kays et al The small home ranges and large local ecological impacts of pet cats. Animal Conservation 11 March 2020 Abstract: Domestic cats are a conservation concern because they kill billions of native prey each year, but without spatial context the ecological importance of pets as predators remains uncertain. We worked with citizen scientists to track 925 pet cats from six countries, finding remarkably small home ranges (3.6 - 5.6 ha). Only three cats ranged >1 km2 and we found no relationship between home range size and the presence of larger native predators (i.e. coyotes, Canis latrans). Most (75%) cats used primarily (90%) disturbed habitats. Owners reported that their pets killed an average of 3.5 prey items/month, leading to an estimated ecological impact per cat of 14.2-38.9 prey ha-1 yr-1. This is similar or higher than the per-animal ecological impact of wild carnivores but the effect is amplified by the high density of cats in neighborhoods. As a result, pet cats around the world have an ecological impact greater than native predators but concentrated within ~100m of their homes.


Cats allowed off their property can get lost, hit and injured or killed by traffic, coyotes, dogs and other large animals as well as being trapped, shot, poisoned, bitten and infected by other cats, notably with feline AIDS and get feline infectious leukemia and other viral infections. Cats with feline panleukopenia have infected and killed endangered Florida panthers.

Indoor cats are upset by cats outdoors their reactions including redirected aggression toward their owners and companion cats in the home; spraying/territorial marking and stress-related cystitis and other health issues such as excessive grooming and house-soiling. These latter behavioral problems can mean abandonment, surrender to a shelter and euthanasia.

Uninformed cat owners who do not neuter their cats, especially young tom cats, often finish up letting their cats out if they do not actually escape, when they start to spray, stink up the home and are hormonally-driven to get outside to mate.

Some of the reasons and solutions to enhance their overall health, safety and well-being are detailed in the American Bird Conservancy’s Cats Indoors Program: “Ever since the invention of kitty litter, cat owners have realized the many benefits of keeping their furry companions safely indoors, on a leash, or otherwise safely contained. This transition has enabled cats to live longer and healthier lives, resulting in fewer trips to the veterinarian and extending the years of mutual companionship. Keeping cats safely contained also protects birds and other wildlife from a cat’s instinctive predatory drive.” For details, and for local Humane Societies and cat rescue organizations to promote visit

The Association of Fish and Wildlife Agencies (AFWA), in collaboration with American Bird Conservancy and other partners, has published a comprehensive domestic cat management guide. The “Toolkit to Address Free-ranging Domestic Cats (Felis catus) on Agency Lands Managed for Native Wildlife and Ecosystem Health” covers a range of topics including predation and disease concerns, legal and policy issues, and management solutions. The toolkit is the result of work by AFWA’s Feral and Free-ranging Cat Working Group, which will soon release more detailed guidance on model policies and an updated AFWA resolution on the control of free-ranging domestic cats. Schweitzer, S.H., and C.M. Gillin (eds.) 2020. Toolkit to Address Free-ranging Domestic Cats (Felis catus) on Agency Lands Managed for Native Wildlife and Ecosystem Health. 32 pages.

One Health is a collaborative strategy, supported by the Centers for Disease Control and Prevention, for achieving optimal health outcomes that recognizes the interconnectedness of domestic animals, wildlife, the environment, and people. American Bird Conservancy recently published an overview of One Health and its relationship to the Cats Indoors program. See One Health, Domestic Cats, And Zoonotic Diseases Grant Sizemore August 30, 2021

Mr. Sizemore writes “Our Cats Indoors program educates the public and policy makers about the many benefits to birds, cats, and people when cats are maintained indoors or under an owner’s direct control. In addition to advocating for responsible pet ownership solutions, we also oppose Trap, Neuter, Release (TNR) for feral cats because of the persistent and severe threats posed by these cats on the landscape.” Kwame Anthony Appiah, writer of the New York Times “The Ethicist” column, reported on the ethics of keeping cats indoors. Appiah commented that “responsible animal-rights groups now agree that our feline companions should not be left to roam free.”

Many people have improved the quality of life and overall well-being of their cats by first, having two or more cats rather than one, and secondly, providing access via a flap door set in a window pane or outside door to an enclosure as per the various “Catio” designs provided by the company Catio Spaces. Catio Plans range from $39.95-$69.95 and 10% is donated to animal welfare organizations. See DIY Catio Plans: Catio Spaces also offers free catio tips. Visit www.CatioSpaces.comto learn more.


Diseases transmissible from cats to humans include: Capnocytophaga, Chlamydiosis, ,Leptospirosis, MRSA resistant Staphylococcus aureus, Streptococcus A, Tuberculosis, Pasteurellosis, Plague, Salmonellosis, Yersiniosis, Tularemia, Cat flea typhus, Sporotrichosis, Cat scratch fever,(Bartonellosis) Ringworm ( Dermatophytosis), Malassezia dermatitis, Chaga’s disease (American trypanosomiasis),Giardiosis, Dipylidiasis, Echinococcosis, Larva migrans, visceral, Larva migrans cutaneous, Strongyloides, Acariasis (mange), Rabies.( Ref: The Merck Veterinary Manual, 2010). Cats have infected people with influenza virus and vice-versa.

Cat feces can contain pathogens transmissible to humans and other species, wild and domesticated, be they around farms, in rural, suburban, urban or slum communities. In the latter there may be a trade-off where a lack of sanitation and high rodent numbers are a threat to public health slightly offset by cats’ predation on infective wildlife. See ‘Outdoor fecal deposition by free-roaming cats and attitudes of cat owners and nonowners toward stray pets, wildlife, and water pollution’ by Haydee A. Dabritz, et al Journal of the American Veterinary Medical Association July 1, 2006, Vol. 229, No. 1, Pages 74-81 There are several diseases that can be passed on to humans from cats’ feces, detailed by Cornell University College of Veterinary Medicine:

Toxpoplasmosis is a cat-originating disease. More attention needs to be given to cat-to domestic animal disease transmission as with Toxoplasma in cat feces contaminating farmed animal feed and passing the disease on from infected cattle and sheep in their meat to humans. Cats around zoos also pose a risk of Toxoplasmosis spread to captive wildlife species.

Cat owners, meat eaters and livestock keepers need to take this statement to heart: “Approximately one-third of the world’s human population is seropositive for the apicomplexan protozoan parasite Toxoplasma gondii. Members of the cat family (Felidae) are the only known definitive hosts of T. gondii, yet the parasite can infect all warm-blooded animals as secondary or intermediate hosts [1].

Toxoplasmosis can have a profound impact on human health, not only in terms of congenital disease in infants, severe pathologies in immunocompromised individuals (eg, organ transplant recipients and people with AIDS) [2], and acute, symptomatic infections in adults during outbreaks [3–5], but also through its association with a large burden of behavioral and neurological disorders, including schizophrenia, in immunocompetent individuals [6–9].

Toxoplasma gondii is also of major economic importance for the livestock industry, being responsible for approximately 23% of ovine abortions in Europe and the United States [10].” From the report Toward Improving Interventions Against Toxoplasmosis by Identifying Routes of Transmission Using Sporozoite-specific Serological Tools by Gregory Milne, Joanne P Webster and Martin Walker Clinical Infectious Diseases, Volume 71, Issue 10, 15 November 2020, Pages e686–e693,

Birds of Prey Infected with Cat Parasite

Scientists Sawsan Ammar et al report in their article, Toxoplasma gondii prevalence in carnivorous wild birds in the eastern United States, (International Journal for Parasitology: Parasites and Wildlife,15: 153-157, 2021) They collected carcasses and tissue samples from ten species of raptor among three states (FL, PA, TN) to determine infection prevalence with Toxoplasma gondii. Overall, 32 of 155 birds (20.6%) tested positive for T. gondii exposure. Birds from the order Strigiformes (3 species) had the highest seroprevalence (75.0%), followed by Falconiformes (5 species; 44.8%), and Ciconiiformes (2 species; 3.8%). Barred Owls (Strix varia) had the highest seroprevalence (77.8%). Although raptors have been considered largely resistant to toxoplasmosis, more research is needed on subclinical disease. Furthermore, the exposure rates of raptors may be useful indicators of environmental contamination with T. gondii. The raptors in this study were likely exposed through consumption of infected prey tissues from other birds, small mammals, or insects.

Some have dismissed these concerns emphasizing that infected cats are only infective for a short time. But in actuality they shed Toxoplasma in the environment ( contaminated food, water and soil) can remain infective for many months. Cats become infected when they kill and consume mice and other small mammals carrying the infective intermediary cysts of Toxoplasma, and when fed infected raw meat. Also, recovered cats no longer shedding this pathogen can succumb to this disease and may start shedding again when this dormant pathogen in their bodies multiplies when the cats are stressed and immunocompromised.

Bartonellosis, commonly called cat scratch fever, is now being recognized as a potentially serious bacterial human disease (causing various inflammatory diseases as of the heart, brain and joints) contracted from cats contaminated with flea feces. This bacterium is harbored by fleas and transmitted in their feces to cats’ claws, skin and oral cavities. (See K Burns Bartonellosis: A zoonosis hidden in plain sight. JAVMA 258:1170-1175, 2021.).

Preventing this disease is not feasible when owned cats are allowed outdoors because they are likely to pick up and bring home fleas. Anti-flea drugs, many putting cats at risk from toxicity, that do not immediately kill on contact but must first be ingested by the fleas from the blood of orally medicated cats are no insurance against Bartonellosis and other flea-borne diseases such as typhus and plague. Humans, infants in particular, while playing on the floor, may accidentally swallow a flea infected with Dipylidium tapeworm larvae and become parasitized.

Visceral larva migrans (VLM) or toxocariasis is a zoonotic infection usually caused by dog or cat round worms of the Toxocara genus. The eggs passed out in the feces are ingested and then hatch into larvae, which penetrate the intestine and start migrating. Because humans are not the definitive host, the larvae cannot mature, and so continue migrating for months or years.

There are two clinical syndromes of infection: VLM and ocular larval migrans (OLM). The symptoms of VLM are related to the organ invaded, most commonly the liver, lung, (asthma being a common symptom) or other thoracic or abdominal organ. VLM usually affects children <5 years old, often from ingesting Toxocara eggs in free-roaming cats’ feces deposited in sand boxes and other play areas. (Visceral Larva Migrans - an overview | ScienceDirect Topics › medicine-and-dentistry).


People who share a bed with, cuddle and kiss cats and dogs while sick with COVID-19 are more likely to pass the disease to their pets, researchers report in Emerging Infectious Diseases. (1). Lead author Prof. Dorothee Bienzle from the University of Guelph’s pathobiology department said results suggest that cats have a higher rate of COVID-19 infection than dogs, stating to the press “It has to do with how well the virus latches on to the receptor in the cat or dog’s respiratory system,” said Bienzle. The high prevalence of COVID-19 antibodies in cats surprised researchers, she said. “We did not expect quite that many,” she said. “Over half of the cats that live in a household of a person who had COVID had antibodies. That’s very high.”(2)

This timely study confirms what I and others with veterinary, medical and scientific background and understanding of epidemiology and zoonoses advocate: All owned cats should be contained/enclosed and not allowed to go off their owners’ property. This would help prevent local wildlife and stray and feral cats from being infected with the SARS-CoV-2 virus and becoming a public health risk as reservoirs of potential infection for years to come. Also, cats infected by humans with this virus could pass on the infection to people as happened in Thailand. (3).Virologists have established that a cat belonging to a COVID-19 positive family sneezed in the face of a veterinarian testing the cat for this disease. Such cases of cat-to-human transmission are probably rare, and researchers emphasize that people should care for their cats — and perhaps take extra precautions when handling cats that might be infected — and not abandon them.


1.Bienzle D, Rousseau J, Marom D, MacNicol J, et al). Risk Factors for SARS-CoV-2 Infection and Illness in Cats and Dogs1. Emerg Infect Dis. 2022 Jun;28(6):1154-1162. 2022.

2.CTV News (Canada)/The Canadian Press (626)

3.Sila, T Sunghan,J. Laochareonsuk.W et al Suspected Cat-to-Human Transmission of SARS-CoV-2, Thailand, July–September 2021 Emerg. Infect. Dis. 28, 1485–1488 2022

Blood samples from 8% of cats being treated for unrelated conditions at the University of Minnesota veterinary college clinic tested positive for COVID-19 antibodies. (Star Tribune, Science & Health. p.2, July 25th 2021).

These studies underscore the importance of not letting cats roam free because of the possibility of human-infected cats infecting other cats and wildlife and then establishing a reservoir of infection in the community. The first medicine and principle of One Health is prevention. This responsibility needs better coordination between State and Federal agencies responsible respectively for domestic animal health, wildlife management and protection and public health. A lack of coordination is evident in a recent review of programs and policies with regard to cats-at-large, domestic cats being allowed to roam free from their homes or becoming feral as wildlife predators.

Veterinarians in private practice, in contrast to those in public health, may not wish to alienate their clients by insisting them to keep cats indoors and providing educational materials. This money-driven lapse in professional responsibility needs to be rectified along with educating those veterinarians who contend that letting owned cats become indoor-outdoor animal companions is best for their overall health and welfare. For more details see the 2019 American Association of Feline Practitioners report Feline Zoonoses Guidelines available at

Local veterinarians and their State Associations need to engage with community animal control and shelter/rescue organizations to more effectively educate and appropriately legislate responsible care of owned cats who should never be allowed to roam off their care-givers’ property. This is not allowed for owned dogs and the same should be applied for owned cats