January 22, 2007

Trichomoniasis Genome Sequenced

ray parasite attached to vaginal cell on left is flat, while a parasite that's not attached, on right, is pear-shaped

Researchers have decoded the genetic makeup of the parasite that causes trichomoniasis, one of the most common sexually transmitted infections (STIs). The accomplishment will help researchers understand how the parasite has become increasingly drug resistant and will likely suggest strategies for new treatments, diagnostics and potential vaccines.

Trichomoniasis affects both men and women, causing roughly 7.4 million infections in the U.S. each year, according to the U.S. Centers for Disease Control and Prevention (CDC). In women, infection commonly occurs in the vagina, resulting in vaginal discharge, odor, irritation, discomfort and, in rare cases, lower abdominal pain. In men, trichomoniasis is most common in the urethra, but infected men often don't have symptoms. Those that do may experience irritation inside the penis, mild discharge or a slight burning sensation after urination or ejaculation.

The parasite that causes trichomoniasis, Trichomonas vaginalis, attaches to cells lining the urinary or genital tract, flattens out and then begins to ingest the cells, along with white and red blood cells, causing direct damage to the urinary and vaginal tissues and resulting in inflammation. The highly predatory parasite also consumes bacteria, including those necessary for maintaining a normal healthy environment in the vagina.

Women infected with the parasite become more susceptible to infection by HIV and other STIs. Pregnant women with trichomoniasis are more likely to deliver low-birth-weight or premature infants. Men with trichomoniasis have an increased susceptibility to HIV infection as well. Although the prescription drugs metronidazole and tinidazole usually cure the disease, drug resistance has become a growing concern.

The results of the T. vaginalis sequencing project, which was funded by NIH's National Institute of Allergy and Infectious Diseases, were detailed in the January 12, 2007, issue of Science.The researchers found a large and highly repetitive genome made up of nearly 26,000 predicted genes.

The decoded genome revealed about 800 genes for surface proteins that likely enable T. vaginalis to adhere to cells in the urinary and genital tracts and cause infection. The researchers were also able to analyze genes thought to be linked to the parasite's unusual metabolism, which is the target of the two drugs used to treat trichomoniasis. They identified possible ways the parasite may become resistant to these medications.

"Although trichomoniasis is very prevalent as a sexually transmitted infection, it has not received the attention given to other STIs," said Dr. Jane M. Carlton, who led the project while at The Institute for Genomic Research. "By better understanding the parasite's genetic structure, we hope to better understand how best to prevent and/or treat the infection it causes."

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