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October 9, 2007
Genome of Common Intestinal Parasite Sequenced
What do children in daycare and hikers have in common? They are both prone to catching the intestinal parasite Giardia lamblia. Now, scientists have revealed its genetic secrets, paving the way to new treatment methods and possibly new vaccines.
Giardia is a strange-looking parasite that is responsible for more than 20,000 reported infections a year in the United States. Its lifecycle is divided into two parts, known as the "cyst" and the "trophozoite" phases. In the cyst form, the parasite can exist in fresh water for long periods without food — and turn an innocent sip from a fresh pristine spring into a nightmare. The cyst turns into the trophozoite form in the warm acidic juices of the stomach. It then swims into the intestine and attaches to the intestinal wall, where it absorbs fats and nutrients.
Many people with Giardia infections never even know they have it, and the infection resolves on its own. About half of those infected, however, develop severe nausea, diarrhea, bloating and abdominal cramping. Because trophozoites absorb fats and nutrients, infection with Giardia may have serious complications such as poor nutrient absorption and weight loss. Although drugs are available for treating the infections, researchers have been concerned that Giardia, like other microbes, could develop resistance. By understanding the genome of the pathogen, researchers could develop new drug targets.
An international team of researchers, led by scientists at the Marine Biology Laboratory in Massachusetts and funded by NIH's National Institute of Allergy and Infectious Diseases (NIAID), described the complete genetic material (the genome) of the parasite in the September 28, 2007, issue of the journal Science.
"The Giardia lamblia genome shows us that the parasite has a large complement of unusual proteins that are potential targets for new drugs or vaccines," says NIAID Director Dr. Anthony S. Fauci.
Besides providing new targets for drugs and vaccine development, the complete genetic sequence of this parasite also sheds light into its evolutionary past. Interestingly, the Giardia genome is compact, with simplified forms of many cellular processes.
The Giardia genome has been deposited into a public database for genetic sequences maintained by the National Center for Biotechnology Information at NIH's National Library of Medicine (http://www.ncbi.nlm.nih.gov/Genbank/GenbankSearch.html). This free scientific resource will help with future research and the development of new drugs.