THE MERCK VETERINARY MANUAL
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Prevention of Zoonoses

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Humans can be protected from some zoonoses by eliminating the pathogen from its animal reservoir(s). In some countries, livestock diseases such as bovine and porcine brucellosis and bovine tuberculosis have been eradicated, and the prevalence of Salmonella in poultry has been significantly reduced. Vaccination (eg, rabies), treatment of clinical cases, flea and tick control, periodic testing for enteric parasites or other pathogens, and other disease control measures in domestic animals can also protect humans. Human vaccines are available for a few diseases, and arthropod control measures decrease the risk of vectorborne infections.

Foodborne zoonoses can often be interrupted by using good sanitation and hygiene during food preparation, eliminating cross-contamination of foods, cooking all foods of animal origin (including invertebrates such as mollusks and snails) to safe temperatures, and thoroughly washing vegetables shortly before eating. Prions cannot be destroyed by cooking; meat inspection and elimination of the pathogen from animals remain the only ways to reduce the risks from these agents. Modern water treatment procedures eliminate most waterborne zoonoses. Where such facilities are unavailable, drinking water should be boiled, filtered, or otherwise treated to remove pathogens. Accidental ingestion of lake or stream water should be avoided. The contamination of irrigation water used for agriculture has become an increasing concern with the rise of pathogens such as Escherichia coli O157:H7. Measures such as composting livestock manure before spreading it on fields may lower the risks from this source. However, post-harvest procedures to eliminate contamination are also critical.

It is often difficult to avoid diseases acquired from the environment. However, measures to eliminate skin contact with soil, such as the use of gloves when gardening and avoidance of dust inhalation, are helpful.

During contact with apparently healthy animals, good hygiene (including hand washing) is an important preventive measure. Hand washing is particularly important before eating. In fairs, petting zoos, or other environments where the public may contact animals, hand-washing facilities should be provided, and eating or drinking in the animal areas should be discouraged. Children <5 yr old should be supervised closely: their immune systems are generally more vulnerable to pathogens, they are less likely to follow sanitary precautions, and they are more likely to engage in behaviors such as tasting dirt. Detailed zoonosis control programs for various types of facilities have been published.

Protective measures in veterinary hospitals include barrier precautions (including gloves, protective outerwear, and other personal protective equipment as appropriate), good hygiene, sanitation and disinfection, appropriate disposal of infectious material, and the use of isolation units for animals with known zoonoses. Whenever possible, hand washing should be done with antimicrobial soaps or alcohol-based sanitizers, which are more effective than ordinary soap.

Counseling immunocompromised clients must strike a balance between awareness of the risks from zoonoses and acknowledgement of the human-animal bond and the psychological benefits of animal companionship. If the person chooses to have a pet, the family veterinarian can help make that decision as safe as possible. Topics to discuss include the risks from feeding raw meat or eggs, the prevention of garbage eating and coprophagia in dogs, the importance of flea and tick control, and the dangers of allowing cats and dogs to hunt. Pets should not be allowed to drink nonpotable water, including water from lakes or streams and water from toilet bowls. Claws should be kept clipped short to reduce the risk of scratches, and rough play that might encourage biting or scratching should be avoided. Regular and thorough cleaning of bedding and cages prevents the accumulation of debris that can shelter microorganisms. Clients should be counseled to avoid any direct contact with feces, as well as to practice excellent hygiene when handling the pet. The litter box should be cleaned daily, preferably by a household member who is not immunocompromised, to reduce the risk of toxoplasmosis. Similarly, cleaning aquariums carries the risk of exposure to Mycobacterium marinum and is best done by an individual who is healthy. Regular veterinary visits, with periodic screening for intestinal parasites and/or other zoonotic pathogens as appropriate, are essential for all pets. Pets that develop diarrhea or other diseases should be brought in promptly for diagnosis.

Any new pet should be examined by a veterinarian to ensure that it is not carrying intestinal parasites, mites, dermatophytes, or other zoonotic pathogens. A healthy, unstressed adult dog or cat with a known history and no recent exposure to environments with high concentrations of pathogens is preferable to a puppy or kitten. Immunocompromised persons should avoid contact with reptiles, baby chicks, or ducklings, all of which may shed Salmonella. Avoidance of strays, wildlife, nonhuman primates, and animals with diarrhea or any other illness is particularly important. It is also prudent to stay away from animals in fairs, petting zoos, farms, schools, and similar settings, and to take additional precautions if avoidance is impractical.

Veterinarians have a vital role in educating immunocompromised clients on the risks from zoonotic diseases, as well as the steps that can be taken to decrease risk. Educational materials such as signs and brochures may prompt clients to ask for advice. Educational materials can also be used to warn pregnant women of the risks from toxoplasmosis and other zoonotic pathogens, or to remind clients that their veterinarian can provide help with safe pet selection and zoonosis prevention in households with children. Guidelines on zoonosis prevention for therapy animals used in hospitals and convalescent homes have also been published.

Last full review/revision March 2012 by James A. Roth, DVM, PhD, DACVM; Anna Rovid Spickler, DVM, PhD

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