The incubation period for G.lamblia is around 7-14 days. Transmission is by the faecal-oral route from contaminated water or food sources. Person to person transmission may occur with poor hygiene conditions.

Symptoms include fatigue, loss of appetite, diarrhoea, nausea and vomiting, headaches, and weight loss. Chronic infection may result in malabsorption. Symptoms usually resolve within 2 to 6 weeks; occasionally symptoms will return after several days or weeks. In some cases, infected individuals may develop long-term complications such as reactive arthritis or irritable bowel syndrome.