Merck Manual

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Professional Version

Prevention of Zoonoses

By

Anna Rovid Spickler

, DVM, PhD, Center for Food Security & Public Health, College of Veterinary Medicine, Iowa State University

Reviewed/Revised Feb 2023 | Modified Jun 2023

Humans can occasionally be protected from zoonoses by eliminating the pathogen from its animal reservoirs or reducing its prevalence. In some countries, control programs for production animal or poultry diseases such as brucellosis, bovine tuberculosis Tuberculosis , or salmonellosis Salmonellosis in Animals Salmonellosis is infection with Salmonella spp bacteria. It affects most animal species as well as humans and is a major public health concern. The clinical presentation can range from... read more Salmonellosis in Animals have contributed greatly to decreased exposure of humans.

Other protective measures directed at the animal may include vaccination (eg, rabies Rabies ), treatment of clinical cases, periodic testing for enteric parasites or other pathogens, and other disease control measures. Arthropod control measures, such as flea and tick control programs in dogs and cats, are sometimes valuable; however, some long-term vector control programs (eg, some programs directed at diseases in production animals) are not practical or sustainable. Vaccines for humans are available for a few diseases.

Transmission of 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 decrease 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 enterohemorrhagic Escherichia coli (eg, E coli O157:H7). Measures such as composting production animal manure before spreading it on fields may lower the risks from this source. However, postharvest procedures to eliminate contamination are also critical.

Some diseases acquired from the environment are common to humans and animals (eg, soil-transmitted helminths). Measures to eliminate skin contact with soil, such as wearing gloves when gardening and avoiding 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 or any other hand-to-mouth contact. 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 years 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 risky 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 use of isolation units for animals with known zoonoses.

Prevention of Zoonoses in Immunocompromised Populations

Counseling immunocompromised owners 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 veterinarian can help make that decision as safe as possible. Topics to discuss include the risks from feeding raw meat, fish, 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 decrease 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.

Owners 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 decrease the risk of toxoplasmosis. Similarly, cleaning aquariums carries the risk of exposure to Mycobacterium marinum and is best done by an individual with a healthy immune system.

Regular veterinary visits, with periodic screening for intestinal parasites 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 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. Some amphibians and exotic mammalian pets may also have a higher likelihood of carrying 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 owners 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 owners 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 owners 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.

Key Points

  • Preventive measures directed at the animal host vary with the disease and may include vaccination, disease eradication programs, screening for the agent (eg, enteric parasites), and prompt treatment of disease.

  • Vector control programs can help interrupt transmission of some diseases.

  • Food safety measures, hygiene, and the provision of safe drinking water decrease the risk from foodborne and waterborne zoonoses.

  • Good sanitation and hygiene decrease the risk of infection when interacting with animals or their environments.

  • Immunocompromised individuals should be advised on the risks of common zoonotic diseases and made aware of useful general preventive measures.

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