The roundworm infection you catch from soil, not from other people

Health · Published 3 October 2026 Swipe more like this →

In short: Toxocariasis is a parasitic infection caused by roundworms found in dog and cat feces. While many people carry the parasite without ever feeling sick, it can occasionally cause serious damage to the eyes or internal organs. Understanding how these eggs survive in the environment is key to staying safe.

Toxocariasis is a zoonotic infection, meaning it spreads to humans from animals—specifically dogs and cats. The parasite, known as Toxocara, lives in the digestive systems of these pets and sheds eggs through their waste. Crucially, the infection is not contagious between humans; you cannot catch it from another person like a cold or flu. Instead, the risk comes from the environment. Fresh feces are not immediately infectious. The eggs require a period of incubation in soil or sand, often lasting several weeks or months, before they become capable of causing disease in a human host.

Once these infective eggs are accidentally ingested—often through contaminated hands, unwashed vegetables, or children eating dirt—they hatch into larvae. In most cases, the human immune system handles the intrusion without the host ever developing symptoms. However, if the larvae migrate through the body, they can cause two primary clinical syndromes. Visceral toxocariasis occurs when larvae move into organs like the liver or the central nervous system, leading to symptoms such as fever, wheezing, or abdominal pain. Ocular toxocariasis is a distinct, often more localized form where a larva enters the eye, potentially causing inflammation, retinal damage, or vision loss, typically in only one eye.

Diagnosis can be challenging because the symptoms often mimic other common infections. Healthcare providers typically rely on blood or eye fluid tests to detect specific antibodies produced by the immune system in response to the parasite. While most cases are mild and resolve on their own, severe infections are treated with antiparasitic drugs, and ocular cases may require steroids or surgery to prevent permanent vision loss. Prevention remains the most effective strategy: regular de-worming of pets, prompt disposal of animal waste, and thorough handwashing after outdoor activities or handling animals are essential for reducing the risk of exposure.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

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