U.Va. researcher reports on advances in treatment of a leading parasitic killer

April 16, 2003

In the developing world, one of every 10 children dies by his or her fifth birthday. In the April 17 issue of the New England Journal of Medicine, Dr. William Petri, professor of medicine at the University of Virginia Health System, discusses advances in the diagnosis and treatment of amebic dysentery, one of the leading parasitic killers of young children.

In the review article, Petri reports that bowel and liver disease due to this parasite is epidemic in many parts of the world. Outbreaks in the United States are only prevented by hygienic measures. When water becomes contaminated with the parasite, as it recently has in Tblisi in the Republic of Georgia, then epidemics occur.

"This is a serious problem in developing countries, but also in countries or regions where there is war or social disruption, like in Iraq," Petri says. "Since the infectious cyst is resistant to chlorine and remains environmentally stable for days or weeks, once food or water is contaminated, disease can quickly reach epidemic proportions."

Diagnosis of infection is very difficult. In fact in a test of clinical laboratories in the United States and Canada, the correct diagnosis was made in only one of 10 cases, Petri says. The team at U.Va. has developed the only FDA-approved diagnostic test for Entamoeba histolytica, the parasite that causes amebic dysentery or amebiasis. Use of this test can greatly improve diagnostic accuracy and prevent this treatable parasitic disease from being confused with inflammatory bowel disease, also know as ulcerative colitis or Crohn's disease.

Entaboeba histolytica can live in the large intestine (colon) without causing disease. However, sometimes, it invades the colon wall causing colitis, acute dysentery or chronic diarrhea. The infection also can spread through the blood to the liver and rarely, to the lungs, brain or other organs. This condition can occur anywhere in the world, but it is most common where crowded living conditions and poor sanitation exist, Petri says.

Transmission occurs through ingestion of cysts in fecally contaminated food or water, and can be easily spread person to person. There are an estimated 50 million cases worldwide of amebiasis, with 40,000 to 50,000 deaths annually. Infection is most serious in infants, the elderly and people taking steroids such as prednisone.

"In a perfect world, amebiasis would be prevented by providing clean food and water," Petri says. "However, providing safe food and water for all children in developing countries would require massive societal changes and monetary investment. An effective vaccine would be much more practical." Studies by University of Virginia scientists of Bangladeshi children have shown that children who have been infected once are immune, so Petri feels that developing a vaccine is an attainable goal.

Immunity in children has provided the basis for design of a prototype vaccine at the University of Virginia. It has proven effective in models of amebiasis and could be developed and tested in humans. In the future, such a vaccine may, through the use of plant biotechnology, be a part of an edible vegetable or fruit, such as tomatoes or carrots, Petri says.

University of Virginia Health System

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