OVERVIEW: Giardia is a protozoan parasite that infects the small intestine of cats and can cause diarrhoea. The biotypes that affect cats do not appear to infect humans. Infection is most common in young cats, particularly from multicat backgrounds.
DISEASE SIGNS: Infected cats that develop clinical signs show small intestinal diarrhoea and there may be associated weight loss.
DIAGNOSIS: Diagnosis of infection is usually based on an in-practice ELISA for faecal antigen or zinc sulphate flotation of several pooled faecal samples. Polymerase chain reaction (PCR) tests are available but not used so widely. Infection can be detected in clinically healthy cats so interpretation of a positive result in cats with diarrhoea requires care.
TREATMENT: Fenbendazole or metronidazole are regarded as the treatments of choice. Secondary gut changes may be slow to resolve and so diarrhoea may continue for some time after infection has been eliminated.