Most sexually transmitted infections are caused by viruses or bacteria. STIs caused by viruses include herpes and genital warts, and the viruses that cause them aren’t even technically living organisms – they are pieces of genetic information that are able to infect a host cell. STIs caused by bacteria include gonorrhea and syphilis; bacteria are microscopic, single-celled organisms with relatively simple cell structures.
But some STIs are caused by other types of living organisms. Protozoan organisms are microscopic and unicellular, like bacteria; unlike bacteria, their cell structures more closely resemble that of the so-called “higher” life forms such as animals and plants. While protozoa are considered to be “animal-like,” they are not animals at all – they are single-celled organisms that reproduce asexually. When certain types of protozoans get into your body, they can cause infections – such as trichomoniasis, the most common curable STI among young females (as well as more females over 40 than previously thought). It is estimated that 7.4 million new cases of trichomoniasis occur annually in the United States; worldwide, there are about 170 million cases each year.
Trichomoniasis, colloquially known as trich, is spread by vaginal or anal intercourse, direct vulva-to-vulva contact, and other activities that involve passing secretions from one partner to another (e.g., sharing sex toys or mutual masturbation). Sexually active people can reduce the risk of contracting trichomoniasis by using latex barriers, such as condoms.
It is common not to have symptoms – up to half of trichomoniasis cases are asymptomatic – but symptoms disproportionally affect females and are very rare in males. When symptomatic, females might experience a vaginal discharge (which may or may not have an unpleasant odor), spotting, and itching or swelling in the genital area. A trichomoniasis infection during pregnancy could increase risk for a preterm birth. A symptomatic male might experience discharge from the urethra. Either sex might experience an increased urge to urinate, along with pain during urination. When symptoms appear, they usually show up within four weeks of infection but can take longer. Symptoms can also go away on their own, but that doesn’t mean you don’t need to seek treatment – you may still be infected.
Trichomoniasis is caused by a protozoan organism called Trichomonas vaginalis, which inhabits the urogenital tract. This organism has flagella to move around and doesn’t need oxygen to survive. It can live in the vagina, urethra, or prostate, but is usually kept in check by bacteria that colonize the urogenital tract. However, if the normal pH is altered, it could lead to an imbalance of the regular urogenital flora and an overpopulation of T. vaginalis.
In order to colonize the urogenital tract, T. vaginalis must be able to adhere to the host’s cells, which it is able to do by producing enzymes that degrade the surfaces of the host’s cells. It is possible that T. vaginalis is unable to produce such enzymes unless triggered to do so by an environment with a sufficiently low pH. After adhering to the surface of a host cell, T. vaginalis is able to stretch its body to maximize the surface area between itself and the cell and can interdigitate some of its appendages with the host cell. The organism also eats bacteria (aiding in the imbalance of urogenital flora), its host cells (such as the epithelial cells in the vagina), and red blood cells (which it consumes for the fat and iron content). The cellular damage caused by the organism brings about inflammation, which is thought to increase the host’s risk for HIV infection. The immune response can also lead to symptoms such as pus and the pain and irritation that can accompany it.
A diagnosis is obtained by performing a pelvic exam on females or a urethral swab on males. If you have a vagina, there are a few things you can do to prepare for your exam that will help you receive an accurate diagnosis: do not douche, do not use any kind of deodorant in your genital area, try not to schedule your appointment during your period, and don’t insert anything into your vagina for 48 hours before your appointment. Those who are diagnosed with trichomoniasis, along with their sexual partners, can be treated with a prescription medication, such as metronidazole or tinidazole. Without treatment, an infected person – even a person without symptoms – can continue to transmit the parasite to other sexual partners.
More information can be found at the CDC’s website. You can seek diagnosis and treatment at a Planned Parenthood health center, as well as other clinics, private health-care providers, and health departments.