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The Long-Term Effects of Giardiasis

author image Marie Zhuikov
Marie Zhuikov is an award-winning public relations professional who has been covering medical, environmental, fitness and travel topics since 1984. Zhuikov has a Master of Arts in health journalism from the University of Minnesota, and has produced a variety of products for the Mayo Clinic, Superior National Forest, and the Sea Grant Program.
The Long-Term Effects of Giardiasis
Female in bed feeling ill. Photo Credit KatarzynaBialasiewicz/iStock/Getty Images


Infections of the microscopic Giardia parasites, also known as Giardia duodenalis or Giardia lamblia, usually clear up in two to six weeks on their own. However, repeated infections or infections in people with compromised immune systems can have long-term effects, some of them severe. The infections, called Giardiasis, happen in the small intestine when a person drinks or eats contaminated water or food. Giardiasis can also spread by personal contact with another person.

Malnutrition and Weight Loss

Many people who have Giardiasis don’t know they are infected. According to the American Medical Association, about two-thirds of infected people have no symptoms. Those with symptoms develop them after about seven days. Symptoms include upset stomach, nausea, diarrhea, gas, abdominal cramps and foul-smelling, greasy stools that have a tendency to float in the toilet bowl. The infection makes it hard for the body to absorb nutrients. This can lead to weight loss. Repeated infections are most likely to occur in people who live in developing countries or in backcountry areas with no water treatment. The repeated insults on a person’s digestive system and long-term malabsorption can cause malnutrition, especially in children.

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Stunted Growth

The malnutrition caused by Giardiasis can eventually lead to stunted growth in children. This is a condition where a child’s growth is slowed because the body doesn’t have the nutrients it needs. In an article in the "Children and Poverty Journal," authors Eugene Lewit and Nancy Kerrebrock explain that children who fall below the fifth percentile of the reference population in height for age are defined as stunted. Usually, once the cause of the Giardiasis is removed and the infection is treated with antibiotics, the child’s growth rate should catch up. If the Giardia source is not removed, the growth problem will continue and the child may never regain the lost height. Growth stunting can also delay puberty, negatively affect cognitive development and cause premature death.

Lactose Intolerance

According to the New Zealand Ministry of Health, about 40 percent of people with Giardiasis go on to develop lactose intolerance. Lactose intolerance is the inability to digest lactose, a sugar found in milk. The sugar is normally digested by an enzyme found in the small intestine. When this enzyme is missing, the lactose accumulates in the intestine and ferments. This can cause symptoms similar to Giardiasis: abdominal cramps, flatulence and diarrhea. For some reason, Giardiasis damages the body’s ability to produce the enzyme that digests lactose.

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