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Relationship between T. vaginalis, TVV may be commensal
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Trichomonas vaginalis virus, or TVV, is prevalent in T. vaginalis, infecting almost half of the more than 350 isolates analyzed in a recent study. However, researchers found that TVV-positive isolates were not associated with clinical symptoms, repeat infections or metronidazole resistance in patients, suggesting that the relationship between TVV and T. vaginalis may be commensal.
Infection with T. vaginalis can cause trichomoniasis — the most common nonviral STD in the world.
“The role of TVV in the pathogenesis of trichomoniasis and T. vaginalis is still not well understood despite the wealth of information that has been uncovered,” Keonte Graves, MS, a researcher in the division of infectious diseases at the University of Alabama at Birmingham School of Medicine, told Infectious Disease News.
“Research has shown that T. vaginalis has been becoming more resistant to metronidazole. TVV may not be involved in the resistance, but it appears to make T. vaginalis more sensitive to metronidazole treatment, and as stated before, metronidazole treatment of TVV-positive organisms may lead to increased inflammatory responses in those with trichomoniasis.”
Graves and colleagues analyzed archived T. vaginalis isolates obtained from 355 women participating in a T. vaginalis treatment trial in Birmingham, Alabama, which included an enrollment visit and a test-of-cure visit 4 weeks after treatment. Additionally, 47 isolates were collected at the test-of-cure visit, and in vitro testing for metronidazole resistance was performed for 25.
According to the study, 40% of isolates tested positive for TVV. The researchers observed that the women with TVV-positive isolates were significantly older (P = .01), more likely to smoke (P = .04) and less likely to report a history of gonorrhea (P = .04). They noted that TVV was independently associated with older age and smoking and was less likely to be found in women with a history of gonorrhea.
“These findings need to be further investigated in order to better understand why [and] how the presence and absence of TVV affect how T. vaginalis changes the vaginal microbiota, along with how the different strains of TVV can influence these changes,” Graves said.
Moreover, the researchers did not observe an association between the presence of clinical symptoms or repeat infection with TVV-positive isolates. Of the 25 isolates Graves and colleagues tested for metronidazole resistance at the test-of-cure visit, none of the 10 TVV-positive isolates demonstrated resistance, whereas two of the 15 TVV-negative isolates demonstrated mild to moderate resistance.
“With the findings in our study, the verdict is still out on whether the virus directly affects symptom severity or not,” Graves concluded. “These would be very important topics of interest when it comes to finding more effective drug treatments to clear the infection, as well as how to better combat the symptoms that people experience.” – by Marley Ghizzone
Disclosures: Graves reports no relevant financial disclosures. Please see the study for all other authors’ relevant financial disclosures.
Perspective
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Nicolas W. Cortes-Penfield, MD
T. vaginalis is itself subject to viral infection. The creatively named TVV has four known strains, which can cause coinfections and modulate T. vaginalis virulence factor expression — and possibly clinical severity — in a strain-dependent manner.
The authors sought to ascertain the prevalence of TVV in T. vaginalis from U.S. patients. They found that 40% of 355 isolates banked during a clinical trial had TVV infection. TVV-positive isolates came from women who were older, more often smoked and had fewer gonorrhea coinfections, all modest associations. TVV-positive isolates were not associated with symptom severity, metronidazole resistance or treatment failure. Unfortunately, the authors could not afford to type the TVV strains, a limitation that may have obscured meaningful clinical associations.
This research provokes interesting questions. Has T. vaginalis harnessed TVV as a sort of "plasmid" — a transmissible genetic element allowing it to shift phenotype, adapting to specific niches? If so, might TVV be a novel therapeutic target for trichomoniasis? If we identify a lytic TTV strain, might it have potential as a therapeutic agent? Moreover, do other protozoan human pathogens have viruses, and if so, could the concept of bacteriophage therapy find a new home in parasitology?
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