Giardia is the name given to an infection by the organism Giardia lamblia, a single celled parasitic micro-organism. It can exist in 2 different forms, as an active organism called a trophozoite and as an inactive cyst. The most common way to become infected is to ingest the cysts through contaminated foods or water. The cysts are activated to become the trophozoites by stomach acids and go on to proliferate in the intestines. Cysts are often present in the faeces of those infected and will lead to further spread of the organism. It is very common indeed, perhaps the most common source of infectious diarrhoea. Many adults can become infected and never know as their body deals with the infection on its own. Children and weaker adults tend to suffer the most.

Infection can occur through drinking water, bathing in public baths, drinking from infected lakes/streams, close contact with an infected person, from infected animals, not washing hands etc.

Once in the body, it attaches via a sucker to the intestinal walls where it interferes with the body's ability to digest fats and lactose, leading to fatty, slimy, yellowish, foul smelling stools. Carbohydrates (starches and sugars) encourage it to grow so should be avoided or limited during recovery. Other symptoms include diarrhoea, abdominal pains, flatulence, eggy smelling burps, bloating, vomiting or nausea, loss of appetite, slight fever or no symptoms at all. The infection can be difficult to eradicate if left untreated for a long time.

Healing objectives are to kill the organism and restore the body's vitality.