Controlling disease transmission in animal shelters: Part 1 (Proceedings)


Shelter medicine is specialized herd health medicine for small animals.

Although animal shelters have existed for many years in the United States, it has only been recently acknowledged that it requires special expertise to provide appropriate advice on how to care for animals housed in these facilities. Until the 1990s, shelters often utilized euthanasia as the primary method to control population numbers and disease, and there was limited need for veterinarians to provide their expertise on a regular basis. That has changed as animals are held long term for both legal and ethical reasons. Shelter medicine is specialized herd health medicine for small animals. It is very different from providing care for animals in kennels, pet shops and research facilities and is not covered in the curriculum of most veterinary colleges. The focus of shelter medicine is on disease prevention, not treatment. Private practitioners often underestimate the degree of knowledge required to successfully manage a disease prevention program in a shelter. Animals are relinquished to shelters for a variety of reasons, but regardless of whether they are sick, injured, abandoned or simply unwanted, the input of the veterinary community is necessary to implement appropriate standards of care. In addition to just providing shelter, food, water and basic veterinary care, shelters are expected to implement programs that address the overall physical and emotional health and well being of the animals. A comprehensive shelter medicine health care program must consider shelter design, stress reduction and sanitation in addition to preventive health care measures in order to successfully control disease transmission. The value of small animals in shelters is often measured by emotion not dollars, so it may be difficult to apply large animal herd health principles that were developed with a different agricultural production goal in mind. Most small animal practitioners are unaccustomed to this approach to small animal medicine. Some veterinary colleges like Cornell, UC Davis, Penn, Illinois, Colorado, Wisconsin, Tennessee, etc are offering courses and residencies in shelter medicine. There is ongoing and growing support and interest at the university level for developing special training programs in shelter medicine for students and practicing veterinarians. Continuing education courses are being offered by veterinary conferences, on the Internet through VIN and at various other venues. The Association of Shelter Veterinarians or ASV ( was formed in 2001 and has over 600 members. It is in the early stages of seeking specialty board status from the American Veterinary Medical Association (AVMA).

There are numerous reasons why disease transmission is so difficult to control in animal shelters; the high number and turnover of animals entering with unknown diseases, the variety of ways that diseases are spread, incubation periods and carrier states that make disease difficult to detect, the ability of certain disease agents such as parvo and calici virus to survive long term in the environment, stress, poor staff and volunteer training, high turnover of staff, aging, poorly designed facilities that do not have adequate ventilation or isolation areas for effective disease management, inadequate healthcare program, lack of data/poor data management, lack of financial and human resources, lack of defined, proven protocols of disease control in herd situations, open access to the public, lack of epidemiological data and so on.

In addition, some disease is inevitable in shelters because the interaction between agent, environmental and host factors affects the animal's ability to resist disease. Some host factors include immune status, stress, nutritional state, age, state of health, etc. Environmental factors include overcrowding, poor facility design and air quality, etc. Agent factors include the virulence, shedding pattern, carrier state, route of infection of the pathogen, etc. An effective disease control program must employ management techniques that manipulate environmental factors, exploit the weaknesses of the agent and enhance the strengths of the host.

Effective disease control requires the identification and thorough knowledge of the disease agent in question, including - incubation period, carrier states, shedding period, communicability, ability to survive outside the host, practical methods of disinfection, effective shelter treatment protocols, etc. In the past shelters often treated cases symptomatically in order to save money. However, it is often more economical and saves more lives to perform diagnostic tests to determine what the shelter is dealing with. Knowledge of the agent allows for assessment and development of sanitation, vaccination and management protocols that can save lives. Management efforts should be made to identify the pathogens, remove as many as possible, break the modes of transmission and inactivate the pathogens that survive. Modes of transmission include direct contact, aerosolization, contamination via feces, urine, tears, saliva, droplets, secretions and excretions, vectors such as fleas, ticks, flies, mosquitoes, mice and other vermin. The most common mode of disease transmission in shelters is via fomites, or hands and inanimate objects such as clothing, medical equipment, ropes, collars, toys, etc. Every effort must be made to sanitize the environment and interrupt these modes of transmission in order to keep animals healthy.

A carrier state exists when an animal harbors a disease in its body without outward signs of disease, thus acting as a source or distributor of disease. The inapparent carrier state of many diseases complicates their detection by shelter staff, who often must rely on physical exams only for diagnosis. Most do not have the benefit of a clinical history or diagnostic testing. One serious problem for shelters due to carrier states is that approximately 80% of cats who have recovered from herpes virus respiratory infections will become true carriers who may be viremic for variable periods of time; they will shed virus in their oronasal and conjunctival secretions spontaneously or intermittently with stress, typically 1 week after the stressful incident and lasting up to 3 weeks after the stress. Viral shedding cannot be detected in latent carriers. Also, cats infected with calici virus may be lifelong carriers, or they may recover and stop shedding, but until they do, they may shed virus continuously. In general, they shed for 30 days after infection, and 50% still shed 75 days later. Vaccination does not prevent this carrier state (Gaskell and Dawson 1998). The carrier state of feline upper respiratory viruses has enormous implications for shelters that handle large numbers of cats, treat upper respiratory infections and house cats in groups. Veterinarians must be aware that although sneezing cats may simply be carriers and not indicative of a new infection, they should still be considered infectious.

Viral shedding is a concern in both naturally infected and vaccinated animals. Puppies infected by parvovirus will shed virus on day 3 post-infection, before clinical disease symptoms are observed. They can shed virus in their feces for 12 to 14 days after infection (Sherdig 1994) and carry the virus on their fur for months, so puppies who have recovered from parvovirus infections should be bathed and housed individually for at least 10 days post clinical recovery, before returning to the general population.

There is some controversy over whether vaccination will affect disease testing for parvo virus. This is obviously a problem for shelters that vaccinate dogs on intake as recommended and must test for the disease later. Vaccination will induce viral shedding that some believe will cause false positives on parvo fecal antigen tests starting anywhere from 3 to 7 days post vaccination ( False negatives may be obtained early in the course of the disease if the dog is not shedding antigen or late in the course of the disease, especially if the dog is immune competent enough to produce antigen binding antibodies. Viral shedding periods should always be considered when disease testing, treating and making decisions about housing and adopting animals in shelters.

Some pathogens can survive long term in the environment and are resistant to routine disinfecting. Some examples include parvo and calici viruses, parasitic ova and larvae such as coccidia, hookworms, flea larvae and dermatophyte spores, which can remain in the environment for over one year. Dirt, grass and gravel cannot be effectively disinfected with chemicals and may be contaminated for months by parvo virus and other parasitic ova and larva. Truly effective control requires removal and replacement of these substrates, which can be very expensive. Risk assessment must be considered whenever placing vulnerable animals in these areas after a known or suspected exposure.

Stress is a leading contributing factor to disease, and unfortunately, shelters are inherently stressful! Stress is defined as "the sum of the biological reactions to any adverse stimulus, physical, mental or emotional, internal or external, that tends to disturb the homeostasis of an organism. Should these reactions be inappropriate they may lead to disease states" (Blood and Studdert 1988). Stress can be physical, emotional or environmental; it is caused by changes in diet, routine or environment- all the unavoidable elements of normal shelter life. Animals who are malnourished, pregnant, lactating, injured, sick, infected with parasites or generally diseased and debilitated are physically stressed. Emotional stresses include fear, pain, anxiety, depression, and even boredom, etc. Environmental stresses include wide fluctuations in ambient temperature, excessive humidity, inadequate ventilation, excess noise, and most of all, crowding. Stress compromises immunocompetency of both immune competent and debilitated animals, which then renders the animals more susceptible to disease caused by the opportunistic organisms they may already be harboring or that they are exposed to in the shelter. Efforts must be directed toward reducing stress to maintain animal health. It has already been mentioned that cats who have recovered from herpes virus infection will exhibit clinical signs of upper respiratory infection and shed virus when stressed. This level of stress can be triggered just by moving the cat from one cage to another. Some other readily observable physiological responses to stress include vomiting, anorexia, self mutilation, and diarrhea. Behavioral or emotional responses include depression, aggression, withdrawal, stereotypies, failure to groom and so on. There are also many diseases that are directly stress related. Some examples of canine diseases are parvo, infectious tracheobronchitis complex, Giardia and coccidia; stress related feline diseases include upper respiratory infections, Giardia, coccidia and FIP. The fact that it is extremely difficult to distinguish the symptoms of true clinical disease from those induced by stress poses a real problem for shelters, especially those that utilize euthanasia to manage disease.

Overcrowding should be viewed as a serious shelter problem to be avoided whenever possible, and managed efficiently to minimize its negative impact when it is unavoidable. In fact, in this author's opinion, overcrowding may be the single most important factor contributing to disease spread in shelters because systems of isolation and segregation of animals inevitably break down as a result of crowding, stress levels rise and more disease transmission via direct contact and fomites occurs. Animals must have sufficient space and opportunity to exhibit normal behaviors, be free from harassment by other animals, have separate space for eating, waste elimination and sleeping and so on to in order to thrive. Staff also have less time to clean, feed and tend to animal needs when the shelter is overcrowded. Allowing overcrowding to continue indefinitely almost always results in more disease, more animal deaths and eventually more disease dictated euthanasia.

Temperature, humidity and ventilation should always be maintained at appropriate levels to increase the comfort of each animal and thus minimize stress. Animals that are hypothermic, hyperthermic, or subjected to drafts or wide fluctuations in temperature and humidity are more susceptible to illness. In general, if humans are comfortable, dogs and cats will be also. Excessive noise, lack of sleep and failure to accommodate diurnal and nocturnal habits of dogs and cats can also increase stress levels. The environmental conditions in different areas of the facility should be monitored to ensure the comfort of all the animals.

Some methods for minimizing stress include 1) providing colony housing for healthy, compatible animals to reduce loneliness and boredom 2) minimization of noise, 3) routine timing of procedures (such as cleaning, walking and feeding) using the same staff, 4) proper nutrition for the life stage and condition of the individual animal, 5) shelves, perches and places for cats to hide, 6) toys and 7) access to natural light etc. The lights should be turned off at night to allow the animals to sleep. Environmental temperatures should be kept as constant as possible. Animals should be segregated by species, age and temperament in colony housing situations and monitored for behavioral compatibility; there should always be discrete, single unit housing available for animals with special needs or temperament problems. Special needs animals include those who are emaciated, debilitated, nursing, pregnant, unsocialized, obese, geriatric, etc. If animals are housed outdoors, they must have access to protection from wind, rain, snow, excessive heat, sunlight or cold, predators, malicious acts from humans, etc. Additional bedding should be provided for animals housed outdoors in temperatures below 40°F. In general, exclusive outdoor housing of shelter animals should be discouraged.

Good nutrition plays an important part in bolstering the immune system and reducing stress. In short, the highest quality, nutritionally complete and balanced food that is obtainable should be fed. Food should be wholesome and fresh, and provided in adequate amounts to meet the needs of each individual animal. It should be stored securely so vermin and pests do not have access to it. The temptation to save money by feeding leftover table scraps or poor quality food should be avoided. Donations of food to shelters are not uncommon, but food that is generic, expired or of poor quality is not a bargain. General recommendations are to feed dogs measured amounts in accordance with their size, age and weight, but to feed cats free choice unless they are obese. Juveniles under 6 months should be fed three times a day to meet their energy and caloric needs. Different foods should be available at the shelter to meet these various needs.

In some shelters food is offered as treats to train animals to make them more adoptable and to alleviate boredom. Fresh, potable water should be available at all times. Confinement in shelters does not allow for normal behavioral responses to stress. Housing considerations should allow for animals to manifest their normal coping mechanisms whenever possible. In the case of cats for example, this would include providing perches, shelves, shoeboxes, paper bags and hiding places at least for the first few days in the shelter. The effect of stress on the individual animal and the entire shelter population should never be underestimated, and stress reduction must be a major goal of any shelter health care program.

A poorly designed shelter can have a major negative impact on the health of the animals. Good ventilation is essential to the maintenance of a healthy population. Fresh air is invaluable, however drafts are not. Fans are often a necessity, particularly for shelters without air conditioning or an HVAC system, but they may help spread disease if not properly placed. They should be used judiciously, especially during disease outbreaks. Ultra violet radiation may be helpful and should be available via windows and sunlight. Hepa filters may help reduce the particle load, dust and odors and thus freshen the air, but will not replace a good ventilation system. Commercial units that are professionally installed and maintained should be used for the best results.

Non-porous materials that are durable enough to withstand repeated cleaning and disinfecting should be used in shelters. Foot traffic and work patterns in multi room facilities should go from healthy areas first to disease areas last, or in other words, from areas with the most disease susceptible animals first (puppies and kittens) to healthy, disease resistant (adult) animals and then to already diseased animals last (isolation ward). In considering cage placement, it should be remembered that a cat's sneeze can propel a disease droplet across a span of 4 feet. Although not a primary route of transmission, cat cages should nonetheless be spaced accordingly. Some dogs will bark incessantly if facing other dogs, so barriers should be placed to prevent direct eye contact of these dogs with each other. One simple solution is to move dogs that bark at every distraction away from doors where passersby may inadvertently provoke their excessive barking.

There is no "one size fits all" housing for all shelter animals. There should be different enclosures for juveniles, large and small adult dogs, feral cats, dangerous dogs and so on. Shelters should consider having both group housing and individual cages. New cat arrivals should be placed in quiet areas with hiding places until their stress levels go down. Physically separate rooms that can be used for isolation should be considered mandatory for all shelters. Animals with infectious disease should be housed and treated in designated isolation wards rather than in a common treatment room that they must be transported to. A quarantine area may be desirable for some situations, although research by Edinboro showed that the longer animals stay in shelters, the more likely they are to contract disease. It may be better to get them in and out as soon as possible. "All in", "all out" cohort systems of quarantine are advised if importing or transferring several animals into the shelter at once, especially if they are coming from areas of unknown or high risk of disease. If it is decided to utilize a quarantine, it should be equal to or exceed the incubation period of most shelter diseases-generally 2 weeks.

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