Harvard Gazette (Harvard University) (11.07.12)
Researchers at Harvard Medical School, Brigham and Women’s Hospital, and State University of New York Upstate Medical University have discovered that the Trichomonas vaginalis parasite—the cause of the sexually transmitted disease trichomoniasis—can be itself infected by a virus. Trichomoniasis is a common bacterial STD that affects about 250 million people annually. According to Raina Fichorova—leader of the research team and associate professor of obstetrics, gynecology, and reproductive biology at Brigham and Women’s Hospital— trichomoniasis is associated with serious consequences for women because of inflammation and risks of reproductive disease.
The Trichomonas vaginalis parasite does not invade human cells, but attaches to their surface and feeds on them. The disease may produce no symptoms for a period of time. The virus, trichomonasvirus, infects the bacteria and increases its pathogenicity by stimulating virus-specific inflammatory responses. The increased inflammation can cause women to acquire other STDs including HIV and HPV. Max Nibert, Harvard medical school professor of microbiology and immunology and co-author of the paper, stated that when the protozoa and virus are found together, the result is an increase in the virulence of the protozoa to the human host, leading to exacerbated disease. Nibert explains that the virus-parasite symbiosis is the norm rather than exception with this particular protozoan. About 80 percent of Trichomonas vaginalis isolates carry the virus.
Trichomoniasis is treated with the antibiotic metronidazole, but this only treats the parasite, not the virus. When the parasite is dying or stressed it releases unharmed virions which cause aggravated symptoms that might increase the danger of trichomoniasis to pregnant women and their infants. Additional research is required to understand the viral cycle and structural features that might be vulnerable to drugs and lead to better treatment of this STD. The study titled, “Endobiont Viruses Sensed by the Human Host—Beyond Conventional Antiparasitic Therapy” was published in the journal PLoS ONE (7(11): e48418. doi:10.1371/journal.pone.0048418).