For most people in the developed world, the idea of carrying a parasite feels remote. It is something that happens in other countries, or to people who haven't been careful. Not to someone who eats well, lives in a clean home, and sees their doctor regularly.
But a growing body of peer-reviewed research suggests that two very common lifestyle factors — owning a pet and eating raw fish — are associated with a higher-than-expected rate of internal parasitic exposure, even in people who feel perfectly healthy.
This article summarises the key findings from that research. It is not intended as medical advice. If you have concerns about your health, please consult a qualified healthcare professional.
What Research Says About Pets and Parasitic Exposure
A study published in the journal Pathogens examined the pathogen load in healthy household pets and found that a significant proportion of dogs and cats tested positive for organisms capable of transferring to humans, despite showing no visible signs of illness.
The most commonly identified organism was Toxocara, a roundworm that can complete part of its lifecycle in humans. According to data referenced by the U.S. Centers for Disease Control and Prevention (CDC), an estimated 14% of the U.S. population carries Toxocara antibodies, suggesting prior or current exposure.
— CDC-referenced data
— Frontiers in Veterinary Science, 2025
A 2025 paper published in Frontiers in Veterinary Science found that people living with pets had approximately three times the rate of parasitic exposure compared to those without pets. Importantly, the researchers noted that the majority of cases were asymptomatic or presented with symptoms commonly attributed to other causes.
Note on symptoms: Researchers have observed that Toxocara infection in humans can present with non-specific symptoms including fatigue, mild digestive discomfort, and general malaise — symptoms that are frequently attributed to stress, dietary factors, or other common conditions. This is considered one of the primary reasons the infection goes undiagnosed in many cases.
This does not mean these symptoms indicate a parasitic infection. Many conditions share similar presentations. A healthcare professional is the appropriate point of contact for any diagnostic concerns.
An Italian survey cited in the research found that fewer than half of pet owners were aware that common pet parasites have the potential to transfer to humans. Researchers described this as a significant public awareness gap.
What Research Says About Raw Fish and Parasitic Exposure
A separate body of research has examined the relationship between raw fish consumption — including sushi and sashimi — and internal parasitic exposure.
A study conducted by researchers at the University of Washington, which combined four decades of data, found that the prevalence of Anisakis — a parasitic worm found in marine fish — has increased substantially since the 1970s in several commonly consumed species. The researchers reported an increase of approximately 283 times compared to baseline measurements from that period.
About Anisakis: Anisakis is a genus of parasitic nematode that completes part of its lifecycle in marine mammals and fish. In humans, accidental ingestion of larvae through raw or undercooked fish can occur. The majority of cases are mild or resolve without intervention, though some individuals experience gastrointestinal symptoms. Cooking fish to recommended internal temperatures eliminates the risk. Freezing at specific temperatures for specified durations is also considered an effective preventive measure by food safety authorities.
The research does not suggest that eating sushi is inherently dangerous or that most people who do so will experience adverse effects. Rather, it highlights that the prevalence of this organism in commonly consumed fish has changed significantly over recent decades, and that awareness of this is low among the general public.
Why These Two Findings Are Often Discussed Together
Researchers in integrative and preventive health contexts have begun examining these two exposure routes — pets and raw fish — together, because both share a key characteristic: they are everyday lifestyle factors that most people do not associate with internal parasitic exposure, and both are associated with organisms that may cause mild or sub-clinical presentations rather than dramatic illness.
What Health Authorities Recommend
Neither the CDC nor other major health authorities currently recommend routine screening for Toxocara or Anisakis in asymptomatic individuals. However, they do recommend several practical measures to reduce exposure risk.
For pet owners, the CDC recommends regular veterinary deworming schedules for cats and dogs, thorough handwashing after handling pets or cleaning up after them, and avoiding direct contact between pets and food preparation surfaces.
For raw fish consumption, the U.S. Food and Drug Administration (FDA) recommends that fish intended to be eaten raw be frozen at specific temperatures for specified durations prior to consumption. Many commercial sushi establishments follow these guidelines, though practices vary.
Frequently Asked Questions
The research outlined in this article is intended to inform general awareness. It is not a substitute for professional medical advice, diagnosis, or treatment. Individual health circumstances vary significantly, and any concerns about personal health should be discussed with a qualified healthcare professional.
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