Considerations and Management of Infectious Diseases of Feral Cats
Demographics of Feral Cats
The countries in the world with the greatest absolute numbers, in decreasing order, of populating domestic cats are the United States, China, Russia, Brazil, France, Italy, United Kingdom, Ukraine, Japan, Germany, Canada, and Mexico.33 However, when adjusted for human population, the highest percentages for cat to human population are the United States, followed by most European countries, Russia, Japan, and countries in the Mediterranean basin.44 In the United States, the popularity of cats as companion animals has increased to the point that Americans now own more cats than dogs. The situation of cat overpopulation occurs in the United States and to lesser degree in the other countries mentioned. However, the discussion in this chapter centers on the problems encountered in the United States. The information presented can be applied to any country where feral cats have become established.
Despite the enhanced status of cats as human companions, tens of millions of cats in the United States remain homeless and several million unwanted cats are admitted to animal shelters each year.2,39 The vast majority of these are euthanized because of a shortage of available homes and because many cats are too inadequately socialized to be adopted as pets. These facts have caused animal welfare advocates to explore alternatives for nonlethal management of various types of cat populations.
The lines between loosely owned outdoor cats, friendly stray cats, and feral cats are often blurred. In common usage, the term feral is often understood to include socialized free-roaming stray cats that often share the same space and lifestyle as their unsocialized counterparts. The number of pet cats in the United States was estimated between 82 and 88 million in 2007,9 and approximately 60% of owned cats are allowed outdoors. Although an actual figure is unknown, free-roaming homeless cat numbers are suspected to be similar.28 A figure often used for estimating this population is to divide the human population in an area by 6 to yield the number of cats. Using this formula in the United States leads to an estimate of approximately 1700 unowned free-roaming cats for every 10,000 residents in an area.
Debate about the actual impact of free-roaming cats on the environment, on nonfelid and felid wildlife, on domestic feline health, and as a reservoir of both feline and zoonotic diseases is ongoing. This debate is often emotional, fueled largely by a lack of sound scientific data on which to form credible conclusions. Separating the impacts of owned cats that roam outdoors from those of unowned ones is also difficult. Increasing social awareness toward unowned free-roaming cats has resulted in a new concept of “community” or “village” cats. This terminology describes how cats (and dogs) are regarded in much of the world outside of the United States. In addition to cats that clearly have an identified owner and residence, most communities are also populated by colonies of free-roaming cats occupying a wide spectrum of socialization level and interactions with human society. These cats are “owned” by the community, and the community is their “home.” The National Animal Control Association in the United States recognizes these “community cats” as an integral component of the overall cat population and promotes the development of comprehensive management practices that encompass both owned and community cats.38 Controlling the reproduction of both owned and community cats is recognized as a cornerstone strategy for reducing the number of unwanted cats in animal shelters and in the environment.
Determining the most appropriate control method for feral cats has emerged as one of the most controversial issues in animal control and welfare. Historically, feral cats have been largely ignored by both governmental and humane agencies. It is common for specific cats that have been declared a nuisance to be culled, but few agencies have comprehensive programs designed to decrease the number of feral cats in their communities. The most successful examples of enduring community-wide animal control have incorporated high-profile, nonlethal feral cat control programs into integrated plans to reduce animal overpopulation.25 A growing grass-roots movement has promoted control of feral cat populations through sterilization. The strategy of “trap-neuter-return” (TNR) seeks to sterilize large numbers of cats and return them to their colonies.2,21 Some programs are quite elaborate, including extensive veterinary care, surveillance for infectious diseases, colony registration, monitoring, and adoption of tame cats; others focus solely on sterilization. Whereas most programs are run by small volunteer groups dependent on donations for operating costs, a growing number are operated with public funds by municipal animal control agencies with the belief that sterilization is ultimately more efficient and cost-effective than ongoing extermination.
Risks Feral Cats Pose to Humans
One of the dominant concerns regarding unsocialized feral cats is physical injury to those handling them. In their natural environment, feral cats are wary of humans and will seek to hide or escape if approached. However, feral cats are likely to bite defensively in fear when handled, such as when animal control personnel attempt to capture a cat by hand or to place a cat in a carrier for transportation. For these reasons, safe cat-handling techniques must be utilized. Not only does this protect the safety of personnel, but it also prevents the situation in which public health officials require euthanasia of cats, for rabies examination, that have bitten or scratched humans. Anyone who works with stray animals, including feral cats, should receive prophylactic rabies immunizations. Gloves, and preferably gauntlets, should be worn at all times when handling these cats, to reduce exposure to cutaneous pathogens and body secretions.
The safest method for handling feral cats is to require that all cats be captured and contained in escape-proof wire humane traps, thereby avoiding direct human-feral cat contact. A trap designed specifically for trapping and safely holding feral cats has been developed and is used with a trap-divider comb to confine the cat to one side of the trap during cleaning and feeding (TNR Cat Trap, Tomahawk Live Traps, www.livetrap.com). When cats are presented for veterinary care in these traps, the comb can be used to gently restrain the cat at one end of the trap for accurate anesthetic injection. The traps should not be opened until the cat is recumbent. At the completion of surgery or other procedures, the cat is returned to its trap before awakening. With this system, cats are never handled while conscious. Handling systems that involve transferring cats from one container to another or opening a container to restrain a cat only invite escapes. Feral cats have an uncanny ability to slip loose during handling and can inflict serious injuries during recapture attempts. A loose cat can thoroughly damage the inside of a facility in its frantic efforts to escape.
Cat-Bite Wounds and Rabies
Although the dog is the primary vector of rabies worldwide, widespread vaccination of dogs and reduction of the stray dog population since the 1940s has eliminated canine rabies variant and greatly reduced the number of dogs infected with wildlife variants in the United States. Today, more than 90% of rabies cases in the United States are reported in wildlife, primarily in raccoons, skunks, coyotes, foxes, and bats. Since 1981, rabid cats have outnumbered rabid dogs in the United States, with 300 feline cases reported in 2009 compared to 81 canine cases (see Chapter 20).6 Most feline rabies cases in the eastern United States are associated with the epizootic of raccoon rabies.36 Although dogs account for three quarters of reported animal bites to humans, rabies postexposure prophylaxis is more commonly administered as a result of stray cat bites.5,20,20 Most cat bites are reportedly provoked from stray cats, with adult women more likely to be bitten than children and men (see Chapter 51).20,43,43 This suggests that human exposure to cat bites and cat-associated rabies can be limited by reducing the stray cat population via TNR and by avoiding direct handling of stray cats.36 This is in contrast to dog bites, which can occur when unprovoked pet dogs bite children. Despite continued concern about the role of cats in human rabies exposure, no human cases in the United States have been associated with cats since 1975. However, even when rabies is not a consideration, cat bite wounds are often serious. They most frequently occur on the hands, and risk of infection is highest when puncture wounds occur.10 Public health recommendations include immediate cleansing of the wound, medical attention, and prophylactic treatment with amoxicillin-clavulanate.32 In addition, cat bites should be reported to local public health or animal control authorities so that animal quarantine and rabies prophylaxis can be implemented as appropriate. See Chapter 20 for additional information.
Feline Leukemia Virus and Feline Immunodeficiency Virus
The American Association of Feline Practitioners (AAFP) recommends that all cats should be tested for FeLV and FIV, but also that a positive test result should not be used as the sole criterion for euthanasia.24 The AAFP further recommends that all positive screening test results undergo confirmation. Large epidemiologic studies indicate that FeLV and FIV are present in a low percentage of feral cats and that the prevalence is not substantially different than that reported for pet cats (Table 98-1).27 As expected, male cats are four times more likely to carry FIV than female cats, because biting is the primary mode of transmission. FeLV, which is most commonly spread from infected queens to their kittens, occurs at nearly the same rate in males and females. Testing recommendations for pet cats are difficult to apply to feral cats for several reasons. Because the accuracy of positive test results decreases when true infection prevalence is low, as is the case for FeLV and FIV, up to 50% of positive test results in feral cats may be false-positive. Confirmatory testing is often impractical because these tests require use of a reference laboratory, and results may not be available for several days. The availability of an FIV vaccine has added an additional complication to testing free-roaming cats with unknown vaccination histories. False-positive results from the available tests for FIV antibodies are induced by the vaccine virus. Of primary importance is the cost-benefit ratio of testing a large number of cats in order to detect the small percentage of seroreactors. Because resources are often limited, feral cat-TNR programs focus on mass sterilization as the primary goal. For these reasons, and because sterilization reduces the behaviors most associated with viral transmission, most large sterilization programs for feral cats do not routinely include testing for FeLV and FIV.48 The AAFP retrovirus guidelines acknowledge that testing is optional in TNR programs.24
TABLE 98-1
Prevalence of Exposure to Infectious or Parasitic Agents in Feral Cats and Pet Catsa
| Organism (Diagnostic Test) | Feral Cats | Pet Cats | Region | Reference | ||
| No. Tested | Prevalence | No. Tested | Prevalence | |||
| Ancylostoma braziliense (Obs) | 94 | 85.1% | Rio de Janeiro, Brazil | 23 | ||
| Bartonella henselae (Ab) | 553 | 33.6% | Florida, USA | 31 | ||
| 100 | 93.0% | 76 | 75.0% | North Carolina, USA | 41 | |
| 79 | 41.8% | 69 | 40.6% | UK | 3 | |
| 36 | 38.9% | 20 | 20.0% | California, USA | 8 | |
| Bartonella spp. (Ab) | 101 | 52.5% | 75 | 50.7% | Grenada, West Indies | 12 |
| Cryptosporidium spp. (Ag) | 87 | 6.9% | 66 | 6.1% | North Carolina, USA | 41 |
| Ctenocephalides felis (Obs) | 33 | 42.4% | Rio de Janeiro, Brazil | 34 | ||
| 200 | 92.5% | Florida, USA | 1 | |||
| Cytauxzoon felis (Obs) | 33 | 48.5% | Rio de Janeiro, Brazil | 34 | ||
| Cytauxzoon felis (DNA) | 961 | 0.3% | Florida, USA | 18 | ||
| Dermatophytes (culture) | 136 | 29.4% | Lisbon, Portugal | 11 | ||
| Dipylidium caninum (Obs) | 94 | 85.1% | Rio de Janeiro, Brazil | 23 | ||
| Dirofilaria immitis (Ab) | 553 | 11.6% | Florida, USA | 31 | ||
| 137 | 8.0% | Grenada, West Indies | 13 | |||
| Dirofilaria immitis (Ag) | 553 | 1.3% | Florida, USA | 31 | ||
| 137 | 5.1% | Grenada, West Indies | 13 | |||
| Echidnophaga gallinacea (Obs) | 200 | 5.5% | Florida, USA | 1 | ||
| Ehrlichia spp./Anaplasma spp. (DNA) | 484 | 0.0% | Florida, USA | 31 | ||
| Felicola subrostratus (Obs) | 33 | 39.4% | Rio de Janeiro, Brazil | 34 | ||
| 200 | 1.0% | Florida, USA | 1 | |||
| Feline coronavirus (Ab) | 553 | 18.3% | Florida, USA | 31 | ||
| 49 | 0.0% | 306 | 34.0% | Sydney, Australia | 4 | |
| 80 | 3.8% | 70 | 58.6% | California, USA | 26 | |
| Feline leukemia virus (Ag) | 709 | 1.7% | 9970 | 2.9% | USA, Canada | 27 |
| 20 | 0.0% | 152 | 2.6% | Ottawa, Canada | 30 | |
| 553 | 3.3% | Florida, USA | 31 | |||
| 33 | 39.4% | Rio de Janeiro, Brazil | 34 | |||
| 100 | 4.0% | 76 | 1.3% | North Carolina, USA | 41 | |
| 101 | 0.0% | 75 | 0.0% | Grenada, West Indies | 12 | |
| 185 | 6.5% | Prince Edward Island, Canada | 16 | |||
| 49 | 2.0% | England, UK | 37 | |||
| 80 | 1.3% | 70 | 0.0% | California, USA | 26 | |
| 30 | 16.7% | Peten region, Guatemala | 29 | |||
| Feline immunodeficiency virus (Ab) | 709 | 3.9% | 9970 | 3.1% | USA, Canada | 27 |
| 20 | 5.0% | 152 | 5.9% | Ottawa, Canada | 30 | |
| 553 | 5.2% | Florida, USA | 31 | |||
| 33 | 75.8% | Rio de Janeiro, Brazil | 34 | |||
| 68 | 22.1% | 340 | 7.9% | Sydney, Australia | 40 | |
| 100 | 5.0% | 76 | 3.9% | North Carolina, USA | 41 | |
| 101 | 21.8% | 75 | 8.0% | Grenada, West Indies | 12 | |
| 185 | 7.6% | Prince Edward Island, Canada | 16 | |||
| 49 | 20.4% | England, UK | 37 | |||
| 56 | 5.4% | 35 | 2.9% | California, USA | 26 | |
| 30 | 3.0% | Peten region, Guatemala | 29 | |||
| Giardia spp. (Ag) | 87 | 5.7% | 66 | 4.5% | North Carolina, USA | 41 |
| Helicobacter spp. in feces (DNA) | 101 | 91.1% | 64 | 56.3% | Seoul, South Korea | 15 |
| Isospora felis (Obs) | 80 | 12.5% | 70 | 0.0% | California, USA | 26 |
| Mycoplasma haemofelis (DNA) | 484 | 8.3% | Florida, USA | 31 | ||
| Mycoplasma haemominutum (DNA) | 484 | 12.2% | Florida, USA | 31 | ||
| Mycoplasma spp. (Obs) | 33 | 72.7% | Rio de Janeiro, Brazil | 34 | ||
| Otodectes cynotis (Obs) | 200 | 37.0% | Florida, USA | 1 | ||
| Physaloptera praeputialis (Obs) | 94 | 13.8% | Rio de Janeiro, Brazil | 23 | ||
| Pulex simulans (Obs) | 200 | 4.5% | Florida, USA | 1 | ||
| Rickettsia akari (Ab) | 36 | 11.1% | 20 | 30.0% | California, USA | 8 |
| Rickettsia felis (Ab) | 36 | 8.3% | 20 | 5.0% | California, USA | 8 |
| Rickettsia rickettsii (Ab) | 36 | 25.0% | 20 | 10.0% | California, USA | 8 |
| Rickettsia typhi (Ab) | 36 | 5.6% | 20 | 5.0% | California, USA | 8 |
| Salmonella spp. (culture) | 80 | 1.3% | 70 | 4.3% | California, USA | 26 |
| Sarcocystis neurona (Ab) | 76 | 9.2% | 80 | 7.5% | Ohio, USA | 47 |
| Ticks (Obs) | 200 | 2.5% | Florida, USA | 1 | ||
| Toxocara cati (Obs) | 87 | 20.7% | 66 | 18.2% | North Carolina, USA | 41 |
| 80 | 53.8% | 70 | 4.3% | California, USA | 26 | |
| Toxoplasma gondii (Ab) | 553 | 12.1% | Florida, USA | 31 | ||
| 33 | 60.6% | Rio de Janeiro, Brazil | 34 | |||
| 100 | 63.0% | 76 | 34.2% | North Carolina, USA | 41 | |
| 101 | 27.7% | 75 | 30.7% | Grenada, West Indies | 12 | |
| 80 | 20.0% | 70 | 2.9% | California, USA | 26 | |
| 194 | 24.2% | Lisbon, Portugal | 11 | |||
| 30 | 53% | Peten region, Guatemala | 29 | |||
| 59 | 84.7% | Majorca, Spain | 35 | |||
| Trichomonads (Obs) | 100 | 0.0% | 20 | 0.0% | North Carolina, USA | 17 |
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