Find information about parasites affecting humans, dogs and cats.

One of the most common intestinal parasites worldwide. Roundworms are large nematodes that live in the small intestine and can grow up to 35 cm long. Spread through contaminated soil, food, or feces — especially dangerous in children and immunocompromised individuals.

Flat, ribbon-like segmented worms that attach to the intestinal wall using hook-like suckers. They can grow several meters long and shed egg-filled segments (proglottids) that look like grains of rice in feces or around the pet's rear end.

A microscopic single-celled protozoan parasite that colonizes the small intestine. One of the most common waterborne parasites globally, Giardia forms hardy cysts that survive in cold water for months. It is a leading cause of diarrheal illness worldwide.

A single-celled intracellular parasite that can infect virtually any warm-blooded animal, but cats are the only definitive host where it reproduces sexually. Estimated to infect up to one-third of the global human population, usually without symptoms in healthy individuals.

A serious and potentially fatal parasitic roundworm that lives in the heart, lungs, and associated blood vessels. Adult worms can reach 30 cm in length. Dogs are the natural host; cats are atypical hosts and often have fewer but more unpredictable symptoms.

Head lice (Pediculus humanus capitis) are tiny wingless insects that live on the scalp and feed on human blood. Extremely common in school-age children, they spread through direct head-to-head contact. They are host-specific — human head lice cannot survive on pets.