There are a large number of zoonotic diseases that can potentially affect people, caused by a wide variety of bacteria, parasites, viruses and fungal organisms. People may become infected by a number of different routes. Poor sanitary habits may lead to the ingestion of small amounts of animal waste products and transmission of zoonotic disease. Fecal waste is a source of many bacterial and parasitic infections, and even urine contamination can lead to disease (e.g. Leptospirosis). Ingestion of undercooked food products, skin contact with infectious agents (e.g. ringworm, fleas, mites), and bite wound or scratches are all potential modes of zoonotic transmission.

Many zoonotic diseases are not directly transmitted from animal to people, but they require an intermediate host (vector), such as a flea or a tick, for transmission to occur. The dog or cat brings the vector into the household where humans can become exposed.

Even though many zoonotic diseases include some very common aliments in animals, serious disease in people is relatively uncommon. Certain individuals, however, are at increased risk.

Young children are probably at highest risk because they are more likely to be exposed to animal excrements during play. Additionally, wild animals or cats may defecate in sand boxes where children play. Poor hygiene habits practiced by children also make them naturally at increased risk for many zoonotic diseases.

People with suppressed immune function because of chemotherapy, organ transplants, or immunosuppressive drugs are also at increased risk. Individuals with acquired immunodeficiency syndrome (AIDS) are also more susceptible. In addition, some zoonotic diseases (e.g. toxoplasmosis) that cause only mild or self-limiting disease in healthy people may be life threatening in immunocompromised individuals.

Finally, certain culinary practices may lead to an increased risk of contracting a zoonotic disease. Eating raw or undercooked beef is a common cause of transmission of toxoplasmosis. Eating undercooked eggs may lead to salmonellosis. Hikers that drink unfiltered or untreated water have a greater risk of acquiring giardia.

A good knowledge of the most common zoonotic diseases and routine health care with good husbandry and sanitation practices will significantly decrease the likelihood of either you or your pet acquiring a zoonotic disease. Your veterinarian routinely provides yearly exams, preventative internal and external parasite control programs and vaccinations. These services dramatically reduce the zoonotic potential of disease. Additionally, veterinarians usually provide information and consultation on training and behavioral issues. This advice is extremely important, since the most common zoonotic diseases caused by small animals are bite and scratch wounds.