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There's a reason it's hard to find information on bowel-dwelling protozoan Trichomonas hominis. It really doesn't do very much other than swim around in your intestines. Once you have swallowed this microorganism (sorry, but you would have consumed feces-contaminated food or drink), then it can establish itself in your intestines, in your gallbladder, or especially in hemorrhoids. However, its presence is more likely to be beneficial than harmful.

Trichomonas is a genus of single-celled, flagellated (meaning they have a kind of "swimming" arm) parasitic protozoans. Trichomonas vaginalis causes urinary tract infections. Trichomonas tenax causes infections in the mouths of humans, dogs, and cats. 

Trichomonas hominis, on the other hand, not only doesn't cause symptomatic infections, it even fights Blastocystic hominis, a different microorganism that can cause:

  • Diarrhea.
  • Flatulence.
  • Nausea.
  • Abdominal cramps.
  • Bloating.
  • Loss of appetite.
  • Fatigue.
  • Hives.

The Trichomonas hominis organism is a predator of the disease-causing Blastocystis organism. You might have a mild toxic reaction to the dead germs, but Trichomonas hominis actually helps you feel better, not worse. In unusual circumstances, some people have accumulated so many Trichomonas hominis that they developed constipation and in one case a toddler developed a fatal ear, sinus, and tonsil infection with the parasite, but these cases are very, very rare. However, these cases date from the 1920's, when distinguishing Trichomonas hominis from other infections by microscope examination was not reliable.

Who is likely to get an infection with this parasite?

During the Vietnam War, about 1.3 percent of American troops developed infections with Trichomonas hominis. A study of children in Thailand in 2004 found that 1.82 percent were infected with the parasite. About six times as many people are infected with the Blastocystis parasite that the Trichomonas hominis can treat.

Most people who have access to clean food and water are not going to develop an infection with Trichomonas hominis. However, people who are treated with immune-suppressant drugsfor rheumatoid arthritis, psoriasis, or Crohn's disease need to take extra precautions when traveling to tropical countries where the Trichomonas parasite may be found in water or food. What are the problem medications?

  • azathioprine (Imuran).
  • corticosteroids such as Prednisone (Deltasone, Orasone).
  • cyclosporine (Neoral, Sandimmune, SangCya).
  • monoclonal antibodies, which include adulimumab (Humira), basiliximab (Simulect), daclizumab (Zenapax), and muromonab (Orthoclone OKT3).
These medications reduce immune resistance just enough that the body may not be able to fend off an infection with the parasite, especially if there has been recent surgery in the gastrointestinal tract.

In people who live in the tropics, the parasite is most likely repeatedly reintroduced by exposure to tainted food or drink. In tourists taken these medications, the parasite is most likely to find a home in scar tissue (adhesions) or swollen blood vessels lining the bowel.

Symptoms of infection include:

  • Abdominal pain, usually lower, on both sides, and
  • Joint pain, as the immune system reacts to the infection.

Trichomonas does not get into the bloodstream and travel to the joints. However, the body has just enough immune power to generate antibodies to attack the parasite and joint tissue, and not enough to get rid of the disease. The failed attack on the parasite instead inflames the joint.

Doctors typically treat this infection with metronidazole given by IV, necessitating a hospital stay. It only takes a few days to bring symptoms under control. However, infection can be entirely avoided by making sure to eat only cooked foods and to drink only boiled or bottled water (making sure the bottle itself has not been contaminated) when traveling to countries where many people have Trichomonas hominis infections. It's only likely to be a problem if you have a weakened immune system, but if you do, failure to take appropriate precautions with food and drink can land you in the hospital.

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