Researchers from Harvard Medical School, Brigham and Women's
Hospital and SUNY Upstate Medical University have found that the pathogenicity
of the sexually transmitted protozoan parasiteTrichomonas vaginalis --
the cause of trichomoniasis -- is fueled by a viral invader. Trichomoniasis
infections are more common than all bacterial STDs combined. Annually,
trichomoniasis affects nearly 250 million people, typically as vaginitis in women
and urethritis in men.
"Trichomoniasis is associated with devastating consequences
for women due to inflammation and related risks of reproductive disease,"
said Raina Fichorova, leader of the research team as well as associate
professor of obstetrics, gynecology and reproductive biology at Brigham and
Women's Hospital. "Our future goal is to determine how the viral symbiont
and its inflammatory 'halo' affect the risk of preterm delivery and low birth
weight."
"This is only one of two incidents that we know of for which
the pathogenicity of a protozoan virus has been characterized," said Max
Nibert, Harvard Medical School professor of microbiology and immunology and
co-author of the paper. "When found together, the result is an increase in
virulence of the protozoan parasite to the human host, leading to exacerbated
disease."
This study, which was initiated by a Harvard Catalyst Pilot grant,
will be published online in Public Library of Science (PLOS) One.
Rather than invading human cells, Trichomonas vaginalisattaches
to their surface and feeds on them, sometimes remaining asymptomatic for a
period of time. The virus, called Trichomonasvirus, infects the protozoan and
increases its pathogenic power by fueling virus-specific inflammatory
responses.
Moreover, carrying the protozoan parasite predisposes women to
acquire sexually transmitted viruses, particularly HIV and human
papillomavirus, or HPV, both of which can lead to serious diseases such as AIDS
and cervical cancer, respectively. Fichorova and Nibert have recently obtained
funding from the Harvard University Center for AIDS Research to find out if the
virus itself is directly responsible for increased HIV risk.
According to Nibert, the virus-parasite symbiosis is the norm
rather than the exception with this particular protozoan. Upwards of 80 percent
of Trichomonas vaginalis isolates carry the virus.
"Unlike flu viruses, for example, this virus can't spread by jumping out
of the cell into another one," said Nibert, who has pioneered molecular
biology work on double-stranded RNA viruses, a category that includes Trichomonasvirus.
"It just spreads between cells when they divide or mate."
According to the researchers, it is this double-stranded nature of
the viral genome that contributes to increased virulence of the protozoan
parasite. "The double-stranded RNA seems important to the signaling
process," added Nibert.
Currently, trichomoniasis is treated with the antibiotic
metronidazole. But this treatment is only effective on the protozoan.
"When the medication is used, the dying or stressed protozoa release
unharmed virions, which then signal to the human cells," explained
Fichorova. As a result, the symptoms are aggravated, and this in turn might
increase the danger it poses 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," said Fichorova. "Our complementary expertise,
interdisciplinary team efforts and strong collaboration is the key to our
future success."
Nibert added that basic research on Trichomonas vaginalis is
not nearly as supported as he thinks it should be. "It is unfortunate that
a human pathogen of such worldwide significance has been neglected to such a
degree," he said.
Source:
The above story is reprinted from materials provided
by Harvard Medical School.
Note: Materials may be edited for content and length.
For further information, please contact the source cited above.
Journal Reference:
1. Raina N. Fichorova, Yujin Lee, Hidemi S.
Yamamoto, Yuko Takagi, Gary R. Hayes, Russell P. Goodman, Xenia Chepa-Lotrea,
Olivia R. Buck, Ryan Murray, Tomasz Kula, David H. Beach, Bibhuti N. Singh, Max
L. Nibert. Endobiont Viruses Sensed by the Human Host – Beyond
Conventional Antiparasitic Therapy. PLoS ONE, 2012; 7 (11):
e48418 DOI: 10.1371/journal.pone.0048418
Disclaimer: This article is not intended to provide
medical advice, diagnosis or treatment. Views expressed here do not necessarily
reflect those of Eagle Group or its staff.
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