Toxoplasmosis

Toxoplasmosis is an infection caused by a single-celled parasite called Toxoplasma gondii. Cats are the main host for this organism, and while many cats carry it without showing signs of illness, some—particularly those with weakened immune systems—can develop symptoms. Dogs can also become infected, though they do not shed the parasite in the same way and clinical illness is less common. Owners often arrive at this page because routine testing has detected exposure to the parasite, or because their pet is unwell and toxoplasmosis has been mentioned as one possibility. Signs, when they occur, can vary widely depending on which part of the body is affected—eyes, lungs, nervous system, or muscles. In many cases, the infection remains dormant and causes no trouble at all. This page explores what toxoplasmosis can look like in dogs and cats, what is happening in the body when infection occurs, how it is identified through testing, and the range of approaches that exist when treatment is considered. The goal is to help you understand the condition and the questions that shape decisions around it.