Veterinarians play a crucial role in preventing zoonotic parasitic infections transmitted from pets to humans due to their expertise and regular interaction with pet owners. In the United States, the number of dog and cat owners continues to grow, with approximately 73 million dogs and 90 million cats reported, and nearly 60% of households owning at least one pet. Households with young children have the highest rates of pet ownership. Dogs and cats often carry intestinal parasites that can infect humans through direct contact or contaminated environments, making children particularly vulnerable to these zoonotic infections.
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Veterinarians are encouraged to provide preventive treatments for these parasites and advise owners on reducing transmission risks. This article reviews the modes of transmission and the frequency of zoonotic intestinal parasites among pets in the U.S.
Helminths such as Toxocara canis and Toxocara cati, common roundworms in dogs and cats, can cause larva migrans syndromes in humans upon accidental ingestion of their eggs. Toxocariasis, a prevalent zoonotic infection, shows seroprevalence rates in humans ranging from 1% to 20%, influenced by factors such as age, socioeconomic status, and pet ownership. Annually, toxocariasis contributes to cases of blindness and other illnesses in children. The risk of infection increases significantly in homes with dogs, especially puppies, and is exacerbated by behaviors such as dirt eating.
Hookworms like Ancylostoma braziliense and Ancylostoma caninum are also common in pets, particularly in southern U.S. regions. Human infections occur through contact with contaminated soil, resulting in cutaneous larva migrans, a condition characterized by itchy skin lesions. While diagnosed infrequently in the U.S., eosinophilic enteritis due to hookworms has been noted, particularly in Australia.
Infections from tapeworms, such as Dipylidium caninum, occur mainly in young children who accidentally ingest infected fleas, typically causing mild gastrointestinal symptoms. Meanwhile, Echinococcus species can lead to severe conditions like cystic echinococcosis, particularly in areas where dogs consume infected animal viscera. 42 cases were recorded in Alberta, Canada, from 1991 to 2001, and transmission has been linked to certain cultural practices among various regional populations.
Echinococcus multilocularis is emerging as a concern in North America, particularly among certain populations in Alaska. Its range is expanding, with cases linked to interactions with wild and domestic animals.
Toxoplasma gondii, generally transmitted via contaminated food and water or through undercooked meat, shows antibodies in about 23% of the U.S. population. Congenital toxoplasmosis is the most severe form, potentially causing significant illness in newborns, with estimates of 400 to 4,000 annual cases in the U.S.
The protozoan Giardia duodenalis, found in various hosts including humans, often causes gastrointestinal issues. Lastly, Cryptosporidium species are significant contributors to nonbacterial diarrhea, with potential zoonotic transmission from pets, notably in young and immunocompromised individuals.
Overall, understanding these zoonotic infections and their transmission routes is vital for veterinarians to effectively treat pets and educate owners on prevention. None of these zoonotic parasitic infections are monitored as reportable diseases in the U.S., resulting in a lack of systematically collected data on their prevalence.