Viral symbionts of parasites can increase virulence to host

A team of researchers recently found that parasites can be made more virulent when they are invaded by a virus.

The team of researchers from Brigham and Women's Hospital, SUNY Upstate Medical University and Harvard Medical School found that the pathogenicity of the protozoan parasite Trichomonas vaginalis is increased by a viral invader. The sexually transmitted parasite is the cause of trichomoniasis, an infection that affects approximately 250 million people.

"Trichomoniasis is associated with devastating consequences for women due to inflammation and related risks of reproductive disease," Raina Fichorova, the leader of the research team, said. "Our future goal is to determine how the viral symbiont and its inflammatory 'halo' affect the risk of preterm delivery and low birth weight."

The virus, called Trichomonasvirus, infects Trichomonas vaginalis and causes virus-specific inflammatory responses. The parasite attaches to the surface of human cells and feeds on them. More than 80 percent of Trichomonas vaginalis parasites carry the virus.

"Unlike flu viruses, for example, this virus can't spread by jumping out of the cell into another one," Max Nibert, the co-author of the paper, said. "It just spreads between cells when they divide or mate."

Trichomoniasis is treated with metronidazole, an antibiotic that only treats the protozoan, not the virus.

"When the medication is used, the dying or stressed protozoa release unharmed virions, which then signal to the human cells," Fichorova said.

The medication kills the parasite but can actually increase danger to pregnant women and their children.

"Ahead is more research to better understand the viral cycle and structural features that might be vulnerable to drugs, which will lead to opening new doors for better treatment of trichomoniasis and related diseases," Fichorova said. "Our complementary expertise, interdisciplinary team efforts and strong collaboration is the key to our future success."