Toxoplasma gondii is a protozoan parasite that uses cats as its definitive host, with implications for cat welfare, wildlife populations, and human public health.
For most cats, Toxoplasma infection causes minimal direct welfare impact as cats are well-adapted hosts. However, immunocompromised cats can develop serious disease affecting the eyes, nervous system, and other organs. The welfare dimensions extend beyond individual cats to the broader ecosystem — cats shed Toxoplasma oocysts that can persist in soil and water for years, affecting wildlife including threatened species. Marine mammal populations, including Hawaiian monk seals and southern sea otters, have been affected by Toxoplasma from terrestrial runoff. From an integrated welfare perspective, managing feral cat populations and keeping pet cats indoors not only protects wildlife from direct predation but also reduces environmental Toxoplasma contamination.