Gene map turns up surprises in itchy genital bug

By Maggie Fox, Health and Science Editor

WASHINGTON, Jan 11 (Reuters) - A one-celled parasite called Trichomonas, which causes an itchy and smelly genital infection especially dangerous to women, has nearly as many genes as a human being, researchers reported on Thursday.

They mapped the genome of Trichomonas vaginalis, which causes the most common non-viral sexually transmitted infection, and hope they have found a few chinks in its armor.

Trichomonas, often called "trick", affects at least 170 million people globally. It is not only itchy and unpleasant, but can infect newborns, cause preterm births and small babies.

It also makes women more vulnerable to the AIDS virus, gonorrhea and syphilis and, unlike many other sexually transmitted infections, can be passed along by wet towels or toilet seats.

While it can be irritating to men, and is passed along by both sexes, women suffer more, said Dr. Jane Carlton of the New York University School of Medicine, who led the study.

"If men had itchy penises I reckon this disease would have a lot more money thrown at it than it has. It is thought of as a woman's disease," Carlton said in a telephone interview.

Her team of 66 researchers in 10 countries found the little protozoan has an exceptionally large collection of DNA, with close to 26,000 confirmed genes -- nearly as many as the human genome.

"It was a huge shock," Carlton said.

Researchers are not sure why, but believe it may have something to do with helping the pear-shaped organism migrate from the intestines to the urogenital tract.

Only two drugs, both in the same class, are approved for treating Trichomoniasis infections, which can be symptom-less for years and then break out unexpectedly with a vengeance. The microbe is already resistant to one of the drugs in many cases, the researchers aid.

FINDING CHINKS

But examination of the gene map shows some weaknesses, and also some good ways to perhaps identify it more easily and earlier in patients.

"We found a few chinks in the armor," Carlton said.

Another surprise -- it contains genes that appear to have been passed to the organism from bacteria. This is the first such case scientists have seen.

Although both the parasite and bacteria are one-celled organisms, on the tree of life they are very far apart -- less closely related than humans are to fungi.

These genes allow Trichomonas to synthesize the amino acid cysteine, which in turn allows it to control the amount of oxygen in the environment.

It is by manipulating the environment that Trichomonas does much of its damage, Carlton said.

"The pH shifts towards more alkaline and that makes the vaginal environment not as healthy," she said. An alkaline environment allows HIV and other sexually transmitted infections to take hold more easily.

And the little microbe itself looks and acts in complex ways.

"The organism is really funky to look at," Carlton said. It has four flagella sprouting from its apex, a tail, and an "undulating membrane which like a frilly nightgown," she said.

It flattens itself and sticks tendrils into the wall of the vagina or urethra, Carlton said.

"It starts to secrete a lot of nasty proteases, pore-forming proteins to degrade vaginal tissue," she said.

"It produces hydrogen. That is probably what produces the gray-green frothy discharge from women."

And perhaps the characteristic fishy odor, as well, she said.