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Germs that infect humans

Giardia lamblia

Giardia lamblia

© Joel Mancuso

Microorganism: the protozoa Giardia lamblia

Disease: giardia

Occurrence of the disease

History: van Leeuwenhoek, the inventor of the microscope, discovered this microorganism while he was examining his own feces.

Current situation: in Canada and in the United States, the giardia microorganism is endemic in day care centers. In 1998, 5,519 cases of giardia were registered in Canada of which 983 were in the province of Quebec. Worldwide, nearly 200 million people are infected.

Mechanism of action of the microorganism: the microorganism lives in the environment in the form of a cyst. It enters the body following absorption of contaminated water and moves down to the intestines where the cyst breaks open. The microorganism then attaches itself to the intestinal wall and invades the intestine while multiplying. An accumulation of these microorganisms in the intestines can hinder food absorption.

Symptoms of the disease: some people are asymptomatic, i.e., they have no symptoms. Others, however, have serious diarrhea, cramps, and considerable flatulence, which often lead to weight loss.

Giardia can be either acute or chronic. Intermittent diarrhea is a symptom of chronic giardia.

Incubation period: three to 25 days

Contagious period: the whole duration of the infection. This may extend over several months.

Hosts: humans and possibly rodents, cervidae (deer), cattle, and domestic animals. In Quebec, a large proportion of cattle is infected with Giardia lamblia and they contaminate water with their feces.

Transmission: the microorganism is transmitted through contaminated water.

Discoverer of the microorganism: van Leeuwenhoek

Treatment: some medications exist, such as mepacrine hydrocloride, metronidazole or furazolidone.

Geographical distribution of the microorganism: worldwide

Prevention: adequate treatment of water reserves

Vaccine: not available