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Zoonotic Diseases

Zoonosis are diseases that are transmissible between humans and animals. While the reported instances of transmission of disease between domesticated animals and humans are not that frequent, they nevertheless represent a significant disease prevalence. In addition it is likely that the incidence of zoonotic infections is higher than that reported in the scientific literature because many of the less well understood infections may not be accurately diagnosed by the medical and veterinary professions in first opinion practice. On the other hand, although the following list is formidable - many of the diseases are rare, and based upon statistical evidence, the chances of a human contracting a zoonotic disease from your pet is extremely small.  The diseases mentioned below may be transmitted by direct contact and indirect contact with bodily fluids (urine, saliva, droplet, blood, and semen), hair or skin of an infected domesticated animal or human.  Immunocompromised people can belong to any of the following groups and are more likely to contract a zoonotic disease:

  • Pregnant women
  • Elderly persons
  • Infants/neonates
  • People receiving chemotherapy, transplant patients, or those on immunosuppressive medications (including prolonged courses of corticosteroids)
  • Persons with diabetes mellitus, chronic renal failure, or other chronic conditions
  • Persons with HIV or AIDS
  • Splenectomy patients
  • Those with cirrhosis of the liver or advanced stage alcoholism

Click here for an overview  presentation on  zoonotic diseases

Additional information about  the following Zoonotic Diseases can be found by clicking on the disease name.
Animal bites
Bordetellosis (Kennel Cough)
Dermatophytosis (Ringworm)
Hookworm (Ancylostomiasis)
Roundworm (toxocariasis)
Sarcoptic Mange

Or contact the Center for Disease Control (CDC) at www.cdc.gov/parasites

A zoonotic disease is an infection that is naturally transmitted from vertebrate animals to human beings. Potential zoonotic agents include bacteria, viruses, fungi, internal parasites and arthropods. There are many factors common in animal shelters that make zoonotic disease a particular concern in this environment. For the protection of shelter staff and volunteers as well as that of the public, it is critical that animal shelter professionals be familiar with the most common zoonotic threats in a shelter environment, and the general principles of preventing transmission of zoonotic disease. This guide is intended to familiarize shelter professionals with some of the general considerations in preventing zoonotic disease, and key features of some of the diseases most likely to be encountered in a shelter. Diseases were selected for inclusion because they are either common or potentially very severe. Many of the diseases included are of increasing importance in recent years. Although the focus of this guide is diseases affecting dogs and cats, shelters often care for a wide range of species, from wildlife to livestock. Virtually all species can be carriers of zoonotic disease, and unusual diseases may also be seen in the more common species seen in shelters. This guide is by no means exhaustive.

Factors in a shelter environment that increase the risk of zoonotic disease.

An animal shelter is unlike virtually any other environment in which animals are maintained, and poses unique challenges for the control of infectious disease in general and zoonotic disease in particular. There is often a high degree of turnover of the population of animals in a shelter, meaning that there is always a new group of animals at risk of contracting disease. Stress, poor nutrition, and presence of concurrent disease or parasitic infestation are common problems that increase the risk of transmission of infectious disease and the likelihood that infected animals will shed significant amounts of disease causing agents into the environment. Many shelters struggle to care for animals in older facilities that may be difficult to properly sanitize, and may be characterized by poor ventilation, overcrowding, and uncomfortable temperature extremes, all of which contribute to the ready spread of infection. Treatment with antibiotics, common at many shelters for such conditions as kennel cough and upper respiratory infection, further reduces animals' resistance to some gastrointestinal infections, and can increase the spread of such zoonotic infections as salmonellosis.
In addition to the general difficulties of controlling infectious disease in a shelter environment, certain factors common in sheltered animals specifically increase the risk of various zoonotic diseases. Animals frequently enter shelters without a history of proper veterinary care or vaccination. Zoonotic diseases more likely to occur in unvaccinated animals include rabies and leptospirosis. Many animals in shelters have a history of roaming outdoors, hunting or scavenging. This increases the risk of infection with such zoonotic conditions as echinococcosis, leptospirosis, salmonellosis, and rabies. Animals that have spent time outdoors and received minimal care are more likely to be infested with external parasites. Some external parasites can be directly transmitted to humans (i.e. scabies, cheyletiella), or they can serve as vectors for zoonotic disease such as Lyme disease and Rocky Mountain spotted tick fever. Finally, animals entering shelters are often frightened, disoriented, and of unknown temperament. Staff handling these animals are at increased risk of being bitten or scratched. Besides the injury and infection that can occur due to the wound itself, this can serve as a means of transmitting zoonotic diseases such as rabies and cat scratch fever.

Geneal principles of prevention and control of zoonotic disease in a shelter environment

As described in the individual disease profiles below, many animals infected with and potentially shedding a zoonotic disease show minimal or no clinical signs. Diseases for which animals are usually or commonly asymptomatic include toxocariasis, salmonellosis, leptospirosis, cat scratch fever, and toxoplasmosis. In addition to the existence of clinically inapparent diseases, many animals will continue to shed infectious agent for some time after recovery from clinically apparent disease, as can be the case for ringworm, salmonella, leptospirosis and others. It is imperative, therefore, that shelter staff realize the potential for any animal to be a potential source of infection, and maintain protective measures as a matter of routine, not just when disease is recognized.

General principles of sanitation and infectious disease control apply to control of zoonotic diseases:

1. A fomite is any inanimate object that can spread disease. Fomites include hands, dishes, and tools such as grooming implements and poop scoopers. Hands should be washed and disinfected after animal contact, including indirect contact from cleaning cages, handling dishes or litter pans. Toys, blankets and dishes should be machine washed or discarded between animals, or should go home with newly adopted animals.

2. Special attention should be paid to incoming animal processing areas and exam rooms. Exam surfaces should be cleaned between each animal, and the whole area cleaned thoroughly at least once a day. Areas that multiple animals pass through each day, such as "getting acquainted" areas where animals and adopters meet, should be cleaned after each use and thoroughly disinfected at least once a day.

3. Feces should be cleaned up at least once a day from runs and cages, and should be removed immediately from common play areas and disposed of properly.

4. Feces should be cleaned up at least once a day from runs and cages, and should be removed immediately from common play areas and disposed of properly.

5. Dirt and grass play yards, while aesthetically pleasing, can serve as a reservoir for resistant agents such as roundworm. It is particularly important that puppy and kitten play areas be readily cleaned and disinfected, as these young animals are most likely to be affected by many infectious agents.

6. Routine disinfection should be performed using agents effective against most bacteria and viruses. Acceptable choices include bleach (diluted at 1:32) and quaternary ammonium compounds. Shelter staff should be aware of agents, such as ringworm and many parasitic infestations, that require more rigorous or specific disinfection procedures.

7. Animal flow and handling order should be planned to reduce spread of infectious disease.
Care and treatment of symptomatic animals
Many animals with zoonotic conditions show no outward signs. However, when zoonotic diseases do cause signs, they often present with vague signs similar to other common infectious conditions in shelters. Therefore, extra precautions should be taken whenever handling sick animals. Such preventive measures protect the shelter population as well as human health.

  • Sick animals should be housed in isolation, and the number of staff caring for these animals should be limited.
  • Staff handling sick animals should wear protective clothing, which should be removed after leaving isolation wards.
  • Appropriate diagnostics should be performed when zoonotic disease is suspected.
  • It may not be practical or warranted to isolate animals with mild conditions such as diarrhea, but these animals should be clearly identified as suffering from a possibly infectious condition and should not be walked or socialized in common areas that can't be easily cleaned.
  • Volunteers should be trained to perform a visual health check before socializing with any animal, and notify shelter staff before handling the animal if any sign of disease is noted.
  • When a zoonotic condition is specifically diagnosed or suspected, the animals cage should be clearly posted with the name of the condition and any precautionary measures (such as protective clothing or special cleaning procedures) required.

Parasite and pest control

Internal and external parasites contribute to a state of general ill health and increase susceptibility to infectious conditions. In addition, internal and external parasites may be directly infectious to humans, or may serve as vectors to spread disease. Parasite control increases animals' comfort and adoptability as well as protecting human health.

1. Internal parasite control should, at minimum, include routine treatment of puppies, kittens and nursing mothers for roundworms and hookworms (see discussion below under specific disease descriptions).

2. Ideally, all incoming animals should be treated with an age and species-appropriate product effective against fleas and ticks as needed depending on region and time of year. If this is too costly, severely infested animals should be individually treated.

3. Environmental treatment of group housing and common areas of shelter as needed for flea control.

4. Rodents and insects can spread zoonotic disease, as well as spreading non-zoonotic infections.

5. Food should be stored in sealed containers and not left in runs overnight where rodents are a problem. Further rodent and insect control measures should be undertaken as needed.

Protection of Staff and Volunteers

It is vital that staff and volunteers have the knowledge and equipment they need to perform their jobs effectively while protecting themselves from zoonotic disease.

1. Provide training and continuing education for staff on the risks of zoonotic disease.

2. Provide appropriate clothing and other protective equipment to prevent transmission of disease.

3. Train all staff to wash hands frequently, after handling animals, before eating and at the end of each shift.

4. Post guidelines detailing what to do in case of a bite or suspected zoonotic disease exposure, including phone numbers for medical emergencies, public health, physician and veterinary contacts.

5. Provide staff with pre-exposure rabies vaccination according to Center for Disease Control guidelines. Maintain written records for staff members regarding vaccination status for rabies and tetanus.

Foster care considerations

It is becoming increasingly common for community members (as well as shelter staff) to provide temporary care for animals in their own homes. Often very young or sick animals are most in need of this special care. These animals can greatly benefit from care outside of the shelter, but these are also the animals most at risk for contracting and spreading infectious disease, including zoonoses. Foster home environments are often more difficult to effectively disinfect than shelters, and can become chronically contaminated by durable agents such as ringworm (dermatophytes) or roundworm (Toxocara spp.). Contaminated foster homes can then serve as a focus for infection of the many vulnerable animals passing through that home, and these animals may return to the shelter to spread their new infection to other animals, staff and adopters. Therefore, for the protection of foster care providers as well as shelter animals, special precautions should be taken when placing animals in foster care.

Foster care providers should receive training as described above for staff members regarding zoonotic disease, including written information in foster care training material.

Before being placed for foster care

1. All animals should receive fecal exams (ideally), or if staffing limitations prohibit this, at minimum animals with persistent or severe diarrhea should be screened.

2. All cats, and dogs with skin lesions should be examined with a Woods lamp as well as visually for signs of ringworm. Suspicious lesions should be treated as described below under ringworm discussion.

3. Puppies, kittens and nursing mothers should be dewormed, and a schedule arranged for re-treatment and vaccination.

4. Animals should be treated for fleas and ticks as needed before leaving the shelter to avoid contaminating a private home.

5. Ill animals and animals suspected or known to have a zoonotic condition should be restricted in the foster home to an easy to disinfect area such as a bathroom. Protective clothing should be worn when handling these animals, just as in a shelter. During times when shelters are having frequent problems with infectious disease, these precautions should be extended to all animals in foster care.

6. Several zoonotic conditions are readily spread from aborted tissue, and may cause no other signs in the affected animal (i.e. Q fever, Brucella canis). When pregnant animals are placed in foster care, foster care providers should be advised to wear protective clothing and take extreme care in handling tissue should an abortion occur.

7. Liability and ethical issues associated with placing animals with a known zoonotic condition in foster care should be discussed and a written policy established.

Protection of adopters

As shelter professionals, we have an obligation to protect those people who adopt our animals to the greatest extent possible, both from zoonotic disease and injury from bites or scratches. In addition to ethical considerations, shelters can suffer financial liability when adopted animals transmit disease. Pet stores and veterinarians have been sued for adopting out animals with such zoonotic conditions as ringworm and roundworm, with settlements in some cases over a million dollars2-4. Shelters can ill afford the financial blow or negative publicity that would arise from such a case. Specific liability issues should be discussed with legal council; however, shelters can help protect themselves and the public by ensuring that the public is given non-alarmist but accurate information about the risk of zoonotic disease, and that reasonable efforts are made to identify and control zoonotic disease in the shelter.

1. Post prominent signs encouraging all visitors to the shelter to wash hands after handling any animal and after visiting the shelter. Make sure hand washing stations (sinks or hand-sanitizer dispensers) are readily available in animal areas.

2. Give adopters general written and verbal information on preventing zoonotic disease, such as the importance of hand washing, preventing feces from building up in the environment, maintaining internal and external parasite control, and maintaining a regular program of veterinary care.

3. Advise adopters in writing of any specific steps that have been taken to control zoonotic disease in an individual animal, such as prophylactic deworming, and when any further treatments will be required. Also inform adopters of any exams that have been performed, and whether or not the animal has been examined by a veterinarian.

4. Develop an adoption contract that requires a visit to a veterinarian within a week of adoption, and explain the importance of this in protecting the health of family members as well as the new pet.

5. Include a written statement in the adoption contract stating that the animal's health can not be guaranteed. If the animal has not been examined by a veterinarian, include this statement in the contract, along with the shelter's policy on animals found to be ill soon after adoption.

6. Develop a shelter policy on adopting out animals with known or suspected zoonotic conditions. If such animals are to be adopted out, written material should be provided to adopters on the specific disease, and a waiver should be signed. Be aware that such waivers may not protect the shelter from liability.

7. Provide results of any temperament testing that was performed. Temperament concerns involving aggression or a history of biting/scratching should be treated in a similar manner to diagnosed or suspected zoonotic conditions in terms of potential liability.

Special considerations for immunocompromised people

Many zoonotic diseases are much more severe or even deadly in immunocompromised people. There are many examples discussed in this guide, including bartonella infection (the agent of cat scratch fever), salmonellosis, bordetellosis (kennel cough), and toxoplasmosis. People at increased risk include people with AIDS, people on chemotherapy or being treated for immune mediated disease, people with organ or bone marrow transplants, the elderly, the very young, and pregnant women. General guidelines exist describing ways immunocompromised people can safely keep pets. These are readily available from several sources; for example, PAWS (Pets Are Wonderful Support), in conjunction with the Humane Society of the United States, has produced guidelines which can be found at the PAWS website at www.pawssf.org. Guidelines for people infected with HIV are also available from the Center for Disease Control5. Specific considerations for shelters include the following.

1. It may not be apparent that a potential adopter is immunocompromised, and people may be reluctant to discuss this private issue. Therefore, material regarding immunocompromised people and pets should be readily available and prominently placed to allow for anonymous contemplation.

2. The safest choice of dog or cat for an immunocompromised adopter is an adult animal (over 1 year old) that is current on its vaccinations and was surrendered from a private home with a history of being a well-cared for pet and with no history of roaming loose. The very safest choice would be to facilitate adoption of such an animal directly from its former home, rather than having it pass through the shelter and potentially become infected with a zoonotic condition.

3. Immunocompromised adopters should avoid any animal showing signs of disease or ill health. Animals selected should be free of fleas and ticks and treated for internal parasites prior to going home.

4. As with any new adoption, the animal should be assessed by a veterinarian soon after adoption and appropriate deworming, vaccination and other treatment instituted or continued.

5. Reptiles are not recommended as pets for immunocompromised people, because of the high risk of salmonella infection.