Giardia lamblia is a parasitic protozoan belonging to the group of flagellates. The parasite is found in the small intestine of humans and other mammals, which when excreted by an organism survives as a cyst before being ingested by the next host. Giardia is characterised by the presence of the outer shell which allows it to survive for long periods of time in an external environment and provides resistance to chlorine disinfectants. Giardia’s cysts have the ability to survive for weeks to months outside the body. This protozoan can be spread in numerous ways person-to-person or animal-to-animal contact; however, the most common method of transmission is by water. Giardia infection occurs by the mouth ingestion of the cyst, which may be present in the directly or indirectly contaminated with faeces water. Rivers, creeks, ponds, dams, lakes and pools are examples of potential sources of Giardia. Contamination of drinking water supplies is also known as a common outbreak.

Giardia causes illness known as giardiasis, which symptoms include weakness, fatigue, weight loss, prolonged diarrhoea and abdominal cramps. Giardiasis can affect anyone at any age; however, not every carrier has symptoms but every carrier can pass the disease to others. Person-to-person is the primary root for the infection.