Giardiasis is an intestinal disease caused by a parasite called Giardia lamblia. It is normally transmitted through water which has been contaminated with human feces. The disease is especially common among hikers and backpackers, as they tend to drink from isolated lakes, streams and ponds that may appear crystal clear but are contaminated nonetheless. This disease is not limited to developing countries. It occurs worldwide but at present seems to be particularly prevalent in Russia. It is also more common at present among male homosexuals as it may be spread through oral-anal sexual contact.
Symptoms may be sudden but usually develop slowly several weeks after exposure. They consist of nausea, loss of appetite and weight loss, fatigue and listlessness, and the typical intestinal symptoms of bloating, gasiness, cramps, diarrhea and foul-smelling stools.
Diagnosis is traditionally by a stool examination but sometimes requires more sophisticated tests such as an Enterotest (a swallowed capsule on a string) or upper intestinal endoscopy. There is a new blood test available which shows a lot of promise in diagnosing Giardiasis.
Treatment is most commonly with an antibiotic named Flagyl (metronidazole). Alternatives are tinidazole (Fasigyn, Tindamax), quinacrine or furoxone.