How are zoonotic parasites transmitted from animals to humans and how can transmission be prevented?
Executive summary
Zoonotic parasites—protozoa and helminths that move from animals to people—reach humans through a handful of well-established routes: ingestion of contaminated food or water, direct contact with infected animals or their feces, vector-borne transfer via arthropods, and environmental exposure to contaminated soil or surfaces [1] [2] [3]. Preventing transmission demands layered actions at the personal, veterinary, food‑safety and public‑health levels, guided by One Health coordination across human, animal and environmental sectors [4] [1].
1. How parasites get across: ingestion and foodborne routes
Many zoonotic parasites enter humans when people eat or drink contaminated products: undercooked meat and seafood, unpasteurized milk, or produce tainted by animal feces carry agents like Toxoplasma, Echinococcus, Anisakis and foodborne protozoa—boiling, thorough cooking and pasteurization eliminate most of these risks [2] [1] [5]. Agricultural and “farm‑to‑fork” vulnerabilities allow contamination at multiple points along the production chain, so food-safety measures across farms, processing and households are central to interrupting transmission [5].
2. Direct contact, pets and companion animals as reservoirs
Direct handling of infected animals, contact with pet saliva, urine or feces, and contaminated household environments are routine ways zoonotic parasites move to humans; common examples include roundworms and Toxoplasma linked to cats and dogs [6] [3]. Veterinary care, regular deworming, vaccination where relevant, and hygienic practices such as handwashing and cleaning litter boxes reduce these risks, though socio‑economic and behavioral barriers can limit implementation in some communities [6] [7] [8].
3. Vectors and environment: insects, soil, and water
Some parasites require an insect or arachnid vector—sand flies for Leishmania, mosquitoes for certain filarial worms—or persist as eggs/oocysts in soil and water that infect people who walk barefoot, eat unwashed produce, or drink untreated water [3] [2]. Environmental control—vector control campaigns, insecticide‑treated collars for reservoir dogs, safe water, irrigation and filtration practices—has proven effective in specific settings and is often preferable to blunt measures such as culling [7] [3].
4. System-level drivers and surveillance gaps
Human-driven changes—urbanization, wildlife trade, habitat loss, and global movement of animals and people—increase contact with wildlife reservoirs and novel parasites, raising emergence risk; antimicrobial use in livestock further complicates control by promoting resistance among bacterial zoonoses and can indirectly affect parasite control strategies [9] [10] [5]. Federal and international reviews highlight that surveillance, data sharing and interagency coordination remain patchy, limiting early detection and prevention of outbreaks linked to wildlife and imported animals [11] [10].
5. Practical prevention: an integrated One Health playbook
Effective prevention combines individual behaviors—hand hygiene after animal contact, safe food handling and cooking, avoiding raw dairy, proper disposal of animal waste, and tick/mosquito bite prevention—with veterinary measures such as routine parasite control and vaccination for domestic animals, and environmental interventions including vector control and water safety [1] [6] [12]. Public‑health strategies must add targeted surveillance, education at animal‑contact venues (petting zoos, markets), regulated animal import controls and coordinated One Health policies to address reservoirs and transmission chains rather than relying on single measures like culling [12] [4] [11].
6. Limits, trade‑offs and emerging research avenues
There is no one‑size‑fits‑all solution: interventions are weighed by feasibility, cost and social acceptability and can have unintended impacts on biodiversity or livelihoods; for instance, culling dogs failed to curb visceral leishmaniasis but insecticide collars and integrated control did [3] [7]. Diagnostic advances, better drugs and transmission‑blocking agents show promise, but gaps remain in translating research into scalable, equitable programs—available sources document the need for multidisciplinary surveillance and community‑sensitive implementation rather than claiming definitive fixes [4] [1].