Research| Veterinarian Awareness

The rabies risk associated with feral cat colonies is negligible, but sometimes it still comes up when discussing outdoor cats. Studies show that feral cats are healthy. Their home is outdoors, and they are part of our landscape. Rabies is often misguidedly used to justify the continued use of “roundups” of feral cats, which has resulted in decades of catch and kill schemes. In fact, feral cats are not a reservoir for rabies, and the virus itself is not nearly the threat it once was in the United States. There has not been a single case of a human contracting rabies from a cat in the past 40 years in the U.S.

Despite the hyped-up media attention rabies receives, rabies control efforts are actually a public health victory—there were only 31 confirmed cases of rabies in humans in America from 2003 to June 2013.1 None of those cases were known to have come from cats. Billed as a “killer disease,” rabies cases in humans are highly uncommon and also highly preventable.

Alley Cat Allies has the facts on rabies to shatter the myths about the disease—so that you fully understand and can inform others. Armed with this information, you can spread the word that feral cats are an extremely negligible rabies risk.

Here you’ll find a full-range of information and facts about the rabies virus: its low prevalence in feral cats, that rabies vaccinations are protocol in Trap-Neuter-Return programs, how long rabies vaccines last, the history of rabies in the United States, and information on programs that have been proven effective in targeting the true sources of rabies: wildlife.

What You Need to Know About Rabies

Rabies is an acute viral infection of the central nervous system.

Rabies viruses can infect most mammals and are usually spread when saliva from a rabid animal enters the body via a mucous membrane, a puncture wound, or open cut. Once inside the body, the virus travels from the initial point of contact to the nerves, spinal cord, and, finally, the brain. The incubation period between exposure to the virus and onset of symptoms for humans can last for months, and as long as treatment begins before symptoms arise, rabies can be completely prevented. Once symptoms begin, the disease nearly always turns fatal. However, according to the Centers for Disease Control and Prevention’s Rabies Surveillance in the United States 2010 report, “recent cases of recovery after treatment and abortive rabies virus infection suggest the disease may possibly not be universally fatal.”2

People most often contract rabies via a bite of a rabid animal.

Rabies is transmitted through the saliva or tissue of an infected animal, and this happens most often via the bite of a rabid animal. Infected saliva must enter an open wound or mucous membrane to transmit the virus.

Cases of human rabies are exceedingly rare in the U.S.

Only two human rabies cases were reported in 2010. Over the last decade, just 21 cases of domestically-acquired human rabies have been reported in the U.S.—that’s an average of two cases per year. (Of the 29 total cases reported from 2001 to 2011, eight of the exposures took place in other countries.) Wildlife account for the majority of exposures and make up more than 90% of all reported rabid animals.

A person exposed to a rabid animal can easily be treated to avoid contracting rabies.

Treatment for humans who have been exposed to the rabies virus, called post-exposure prophylaxis (PEP), is completely effective when begun before the onset of symptoms. The incubation period in humans generally lasts three to eight weeks, but can extend even longer if the infection occurred distant from the brain, for instance in a foot.

Rabies shots do not involve a bunch of painful shots in the stomach anymore.

While it’s true that rabies shots given after an exposure once consisted of numerous injections to the stomach, those days are long over. Today, rabies shots are given in the arm and are no more painful than a flu shot. The number of doses required has also changed. In June of 2009, the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention revised their guidelines to recommend a single dose of human rabies immune globulin followed by four booster shots, rather than the five boosters previously recommended.

Wildlife is the number one source of rabies.

Surveillance statistics show that bats are now the number one source of human rabies exposure in the U.S., and that raccoons and skunks are the most commonly infected species, followed by bats and foxes. According to the Centers for Disease Control and Prevention, wildlife have accounted for more than 80% of reported rabid animals in the United States since 1975. Today, more than 90% of rabies cases occur in wildlife—92% of cases in 2009 and 2010.

Cat to human transmission of rabies is rare.

The last confirmed cat to human transmission of rabies occurred more than 35 years ago. While it’s possible for feral cats to become infected with rabies, feral cat colonies themselves do not generally serve as a source of the disease. “We see rabies more often in raccoons and bats than in the cat population,” says Roberta Lillich, DVM, president of the American Association of Feline Practitioners.

Rabies is caused by a virus that exists in several different variants, some of which are specially adapted to specific animal species. For instance, dogs can develop canine rabies, and this canine rabies variant can thrive in unvaccinated dog populations, which in turn may serve as an ongoing source of rabies in a community. But rabies has never developed a specific feline variant, and thus cats are merely incidental victims, says Julie Levy, DVM, PhD, at the University of Florida in Gainesville.

Cat behavior may explain why rabies is relatively uncommon in felines, says Lillich. “Skunks and raccoons are major sources of rabies, and most cats who are faced with a challenge by a skunk or raccoon will run away, whereas a dog is more likely to attack,” she says. When faced with non-prey animals, “cats are generally defensive animals rather than offensive animals,” Lillich says, and the small rodents such as squirrels, chipmunks, rats, mice, and rabbits that feral cats may hunt are rarely infected with rabies. Feral cat colonies managed with Trap-Neuter-Return programs do not harbor rabies, because the vaccinations they receive as part of the program are proven to protect them from the disease for multiple years.

The rabies vaccine has helped to make rabies a public health victory.

“The rabies vaccine has been one of the big public health successes of the past 50 years,” says Susan Dicks, DVM, a private practitioner in Albuquerque who also has wildlife experience. Studies show that rabies vaccines induce a long-lasting immunity, and widespread immunization campaigns for both pets and wildlife have come close to eliminating the disease in cats and dogs. In fact, a variant of dog-coyote rabies that once thrived in Texas was eradicated in the U.S. in 2008, thanks to the widespread use of Oral Rabies Vaccine (ORV) in wildlife. The fact that wildlife, not domestic cats and dogs, now serve as the prime sources of rabies exposure in the U.S. is proof that vaccination programs work. “Rabies will never be controlled or eliminated in the U.S. until effective programs to eradicate rabies in wildlife are carried out,” says Levy. Learn more about Wildlife and Rabies.

Rabies vaccines outlast their expiration dates.

“Even a single dose of rabies vaccination provides years of protection against rabies infection,” says Levy. In one study*, 12-week-old kittens given a single rabies vaccine were completely protected against rabies four years later when they were exposed to the rabies virus, she says. “There is solid evidence that a single rabies vaccine produces multi-year immunity.” (*Note: Alley Cat Allies is against testing on animals, as it is against all cruelty toward animals. There are better alternatives to animal testing—including mathematical and computer modeling or using cultures from cells, organs, or tissues—that are precise and sophisticated.)

Vaccination schedules that require one or three year boosters are based on state and local laws, not evidence about the vaccines’ efficacy, says Lillich. Most local laws require rabies vaccination either yearly or every three years and so vaccine manufacturers tailor their studies and products to these time periods. In fact, one vaccine manufacturer produces multiple versions of the identical vaccine with different labels according to the locally mandated vaccination schedules.

Studies suggest that the vaccines last a minimum of three years, but due to expense and logistics, large-scale studies have never been extended past three years, Lillich says. Some trials suggest that the vaccines last beyond three years, and the Rabies Challenge Fund (RCF) was founded in 2005 to determine the duration of immunity that rabies vaccines provide in hopes of convincing lawmakers to change laws mandating excessive vaccinations. The RCF aims to extend the required interval for rabies boosters to at least seven years. Learn more about Vaccinations and Feline Cancer.

Trap-Neuter-Return programs help control rabies.

By vaccinating feral cats against rabies and preventing the vacuum effect, Trap-Neuter-Return programs, also known as TNR, prevent rabies from infecting feral cat colonies and their communities. Rabies vaccinations provide multi-year immunity, and since feral cats involved in TNR programs are vaccinated and therefore cannot acquire or transmit the virus, they pose no threats to humans or other animals. Learn more about Rabies and Trap-Neuter-Return programs.

Rabies and Trap-Neuter-Return programs

Trap-Neuter-Return programs involve the caring capture, sterilization, and vaccination of feral cats. Those who have been vaccinated and neutered are marked with an eartip, and cats adequately socialized to humans get adopted into homes, while the rest are returned to their colony where a human caregiver often looks after their health and ensures that they receive adequate food and shelter.

Scientific studies show that TNR policies are the most humane, effective way to manage feral cat populations. Feral cats differ from stray cats, because they have never been socialized to humans. Trap-Neuter-Return programs give feral cats who cannot be adopted a chance to live out their lives without posing a disease risk to humans. TNR policies also protect feral cat colonies from the minimal risk of contracting rabies and prevent these cats from spreading the disease.

“Opposition to humane control of community cats via TNR is often based on a misunderstanding of rabies biology,” says Julie Levy, DVM, PhD, at the University of Florida in Gainesville. Some species, such as dogs, can harbor a strain of rabies especially adapted to that animal. When this happens, the species can become a source of rabies virus that is maintained over time.

Cats have never developed their own strain of rabies. “There is no cat-adapted rabies strain that is maintained in the feline population,” says Levy. “All rabid cats are incidental victims and acquire their rabies infections from wildlife.” It’s rarely cats who spread rabies, she says, but unvaccinated wild animals such as raccoons, foxes, and bats. “Rabies will never be controlled or eliminated in the U.S. until effective programs to eradicate rabies in wildlife are carried out,” Levy says. Currently, 18 states are using oral rabies vaccines (ORV) to control rabies in wildlife populations. Learn more about Wildlife and Rabies.

Trap-Neuter-Return programs are part of the solution, says Levy. “In many communities, such as Gainesville, the feral cat TNR programs are the largest provider of rabies vaccines in the community.” Even a single dose of rabies vaccine can provide multiple years of protection.

Rabies Control in the U.S.

Rabies outbreaks were once common in the U.S. As recently as 1946, the U.S. reported 33 human cases of rabies and more than 8,000 cases among dogs. In 1947, a national rabies program was established to tackle the problem. This initial rabies eradication effort focused mostly on dogs, which were originally the most common source of rabies exposure.

In addition to vaccination, early rabies control efforts often involved capturing and killing dogs that were found roaming, says Julie Levy, DVM, PhD, at the University of Florida in Gainesville. But rounding up and killing strays cannot eliminate rabies, because it’s nearly impossible to entirely extinguish a stray population. Removing animals tends to trigger what is known as the vacuum effect and merely opens up territory for new, possibly rabid, strays to move in and continue breeding. Learn more about the vacuum effect.

Instead, it’s vaccination programs that have proven most potent at controlling rabies. Now that rabies vaccination has become common for dogs and other domestic animals, rabies has nearly vanished from these populations. According to the Centers for Disease Control and Prevention, “As canine rabies was controlled and ultimately eliminated, the epidemiology of rabies in the United States shifted to primary circulation in wildlife species.”3 Today, wildlife remains the most common source of rabies viruses, making up more than 90% of reported cases. Communities concerned about rabies should focus on effective wildlife programs, such as the Oral Rabies Vaccine (ORV). In 2008, ORV programs in Texas led to the eradication of the domestic dog-coyote variant of the rabies virus in the U.S.

Programs that combined vaccinations with the killing of stray dogs are sometimes offered as a model for controlling rabies in feral cat colonies, but this approach fails to recognize that dogs carry their own dog-adapted strain of canine rabies that allowed the virus to thrive in stray populations. Cats do not have their own strain of rabies, and Levy says that cats are merely incidental victims that develop rabies from wildlife. Feral cat colonies rarely harbor rabies, and TNR protects them from contracting the disease.

Wildlife and Rabies

According to the Centers for Disease Control and Prevention, wild animals account for more than 90% of reported rabies cases, and bats, raccoons, foxes, and skunks remain the most common sources of rabies in the U.S. In 1997, the United States Department of Agriculture’s Wildlife Services began the National Rabies Management Program to coordinate the distribution and use of oral rabies vaccines in wildlife and prevent the spread of rabies.

The oral rabies vaccine (ORV) is licensed for use in raccoons, gray foxes, and coyotes and is delivered in a so-called bait matrix consisting of a small sachet filled with a dose of rabies vaccine that is anchored to fishmeal or dog food in such a way that an animal that bites into the bait will also receive the vaccine. The bait is then distributed throughout locales with a high number of rabies cases either by aircraft or being placed by hand.

The vaccine has proven an effective method for reducing rabies among wildlife. For instance, as of 20011, ORV programs along the Appalachian Ridge have prevented rabies from spreading westward among raccoons. Since 2005, 6.5 to 9.5 million doses of oral vaccine targeting raccoons have been distributed annually in 15 eastern states. And, the state of Texas’ use of ORV programs beginning in 1995 in response to outbreaks in coyotes and grey foxes has resulted in the elimination of the domestic dog-coyote rabies variant from the US in 2008.

While oral rabies vaccines are not approved for cats and dogs, ORV programs can cut the risk of rabies in feral cat and dog populations by reducing the virus among wildlife species that might spread the disease to these feral populations.

Wildlife is the most common source of rabies exposure in the U.S. According to the Centers for Disease Control and Prevention, wild animals accounted for 92% of reported cases of rabies in 2010.

Vaccinations and Feline Cancer

The switch in 1985 from a rabies vaccine that contained a live rabies virus (modified to make it harmless) to one that used a killed virus (with ingredients added to “up” the immune response it provoked) coincided with a puzzling rise in feline sarcoma, a deadly type of cancer that is difficult to treat. Veterinarians noticed that these sarcomas were turning up near vaccination sites and in 1996, the American Veterinary Medical Association, American Animal Hospital Association, American Association of Feline Practitioners and Veterinary Cancer Society jointly formed the Vaccine-Associated Feline Sarcoma Task Force (VAFSTF) to investigate the problem.

Complete answers remain scarce, but the evidence that’s emerged so far suggests that while the benefits of rabies vaccination still outweigh its risks, veterinarians can reduce the potential for feline sarcoma with certain practices. The VAFSTF recommends that rabies vaccines be given in the right rear limb to reduce the risk of feline sarcoma to cats—making the injection site easier to monitor and care for. The group is looking into other ways to cut the risk even further. Meanwhile, the Rabies Challenge Fund (RCF) was founded in 2005 to determine the duration of immunity conveyed by rabies vaccines in hopes of convincing lawmakers that annual rabies vaccines are excessive.

Currently, rabies booster vaccines are labeled and administered based on local laws, not according to scientific data on the duration of their effectiveness, says Roberta Lillich, DVM, president of the American Association of Feline Practitioners. In fact, one vaccine manufacturer produces multiple versions of the identical vaccine with different labels according to the locally mandated vaccination schedules. Many localities still require yearly rabies boosters, even though existing vaccines have been shown to last years beyond their expiration dates.

“There is solid evidence that a single rabies vaccine produces multi-year immunity,” says Julie Levy, DVM, PhD, at the University of Florida in Gainesville. But finding out exactly how long vaccines can protect against rabies requires expensive, complicated studies and neither vaccine makers nor local governments have much incentive to fund these studies. The RCF aims to fill this gap by funding trials they hope will eventually extend the required interval for rabies boosters to five and then to seven years.

Rabies Laws Cost Animal Lives

Testing for rabies requires killing the animal, since the only way to make a positive diagnosis is by testing brain tissue. But of the 120,000 total animals (of all species combined, not just cats) killed for rabies testing in the U.S. each year, only about 6% test positive. Among domestic animals like cats, the proportion of positive tests is less than 1%.

This killing is entirely unnecessary and all too often preventable. The Centers for Disease Control and Prevention (CDC) acknowledges this on its website: “We have learned that it is not necessary to euthanize and test all animals that bite or otherwise potentially expose a person to rabies. For animals with a low probability of rabies such as dogs, cats, and ferrets, observation periods (10 days) may be appropriate to rule out the risk of potential human rabies exposure.”

Cats who have bitten or scratched a person

The CDC recommends a 10-day confinement for vaccinated and unvaccinated pets, but still advises that any stray or “unwanted” domestic animal who bites a person be killed and tested for rabies. Feral cats vaccinated through Trap-Neuter-Return are protected against rabies, but since they are not owned, in this situation it would be up to animal control (or in some situations, the public health department) to decide whether or not to kill and test the cat.

Cats who have been exposed to rabies

Domestic animals may also be killed and tested if they have been exposed to rabies, but bitten no one. The CDC suggests a minimum 45-day confinement for vaccinated pets that have been exposed—if they show no sign of rabies during this time, they don’t have to be tested. But the CDC advises killing unowned or unvaccinated animals for testing immediately, with no observation period at all. If the owner of an unvaccinated pet refuses to allow the testing, the CDC recommends impounding and quarantining the pet at the owner’s expense for up to six months. Feral cats, however, would likely be killed in this situation.

Cats with “wounds of unknown origin”

Beyond biting or scratching a person or being exposed to rabies by another animal, many states consider any “wound of unknown origin” on an animal as a potential rabies exposure. Rabies testing laws are determined by state and local authorities and enforced by animal control—they vary from state to state and even city to city—but the CDC recommends that authorities immediately kill and test wounded stray or feral animals and wounded unvaccinated pets even if they don’t display signs of rabies.

The recommendations from the CDC are often especially deadly for feral cats and are a huge hindrance to Trap-Neuter-Return. For instance, when feral cats are trapped, they often thrash about in the cage trying to escape, causing superficial wounds on the face or paws—minor injuries that sometimes classify as “wounds of unknown origin” and cause otherwise healthy cats to end up in quarantine.

Also, not all states require cats with wounds of unknown origin to be killed immediately, but many require a lengthy quarantine—Massachusetts, for example, requires a six-month quarantine. For years, organizations like the Merrimack River Feline Rescue Society in Fall River, Massachusetts, have had to quarantine cats brought in for Trap-Neuter-Return with wounds of unknown origin for half a year in accordance with state law, to make sure the cats are not killed unnecessarily for testing.

Outdated rabies laws cost cats’ lives

This distinction between observation for vaccinated cats and immediate killing for testing on unvaccinated cats underscores the importance of keeping accurate rabies vaccine records for feral cat colonies. Even though they are still “unowned,” rabies testing is at the discretion of animal control, so it could be the difference between life and death.

Even for previously vaccinated animals, rabies laws don’t reflect the full effectiveness of vaccines. Evidence shows that even a single rabies vaccine can last much longer than the once yearly booster shots that many local laws require, says Julie Levy, DVM, PhD, at the University of Florida in Gainesville. The CDC compendium recommends that animals with expired vaccines be assessed on a case-by-case basis to determine if they need to be tested, but they miss the point—a healthy animal should never die on a whim.

Quarantining animals for six months or killing them for unnecessary testing is cruel and costly. Rabies laws that encourage killing must be changed to reflect the small number of positive tests in domestic animals and the scientific evidence that vaccines work for much longer than the law recognizes.

 


[1] Dyer JL, Wallace R, Orciari L, Hightower D, Yager P, Blanton JD. “Rabies surveillance in the United States during 2012.” J Am Vet Med Assoc. 2013;243(6):805-15. doi: 10.2460/javma.243.6.805.

[2] Blanton, Jesse D., Dustyn Palmer, Jessie Dyer and Charles E. Rupprecht. Rabies Surveillance in the United States during 2010. Journal of the American Veterinary Medical Association 239 (2011): 773-783.

[3] Ibid.