kirisutogomen | Trichomonad of the Day

The trichomonad of the month is Trichomonas vaginalis.

Like other parabasalids, Trichomonas vaginalis is anaerobic, due to a secondary loss of mitochondria. (Mitochondria are organelles present within the cells of most eukaryotes; they have their own DNA and complex structural elements such as a double membrane because they are actually the relicts of ancient endosymbiotic prokaryotes. They continually speak to us, telling us the will of the Force. When you learn to quiet your mind, you'll hear them speaking to you.)

(Secondary loss is when you don't have some trait that your ancestors did (for example, the last common ancestor of all molluscs had a shell, but octopodes have dispensed with such things (the eggcase of the paper nautilus, which is actually not a nautilus but an octopus, is shell-like but not really a shell (the paper nautilus is also notable for the fact that the male of this octopus species has a detachable penis called the hectocotylus))).)

But T. vaginalis didn't completely lose its mitochondria -- they have really just streamlined and simplified into hydrogenosomes. Where your mitochondria need oxygen to metabolize glucose (actually pyruvate), hydrogenosomes just need the glucose (actually pyruvate) and nothing else, and then output molecular hydrogen and acetate. I really don't have time to get into these but check this out: animals that don't breathe oxygen. Put that in your hat and smoke it! Or, don't, as that would require oxygen for the combustion.

Trichomonas vaginalis was the first parabasalid to have its genome sequenced. It appears to have three times as many protein-coding genes as the human genome, but is only one-twentieth as long. That's not actually all that uncommon -- single-celled organisms usually have most of their DNA as genes that code for proteins, while only 1.5% of our DNA is actual genes. And in general neither length of genome nor number of genes is terribly strongly correlated with the complexity of the organism: the brown mountain grasshopper has a genome seven times as long as ours and 100 times as long as a fruit fly's, almost as long as the genome of the onion.

OK, so it's a protozoan with malfunctioning mitochondria that you're spinning as "simplified". So what? Big deal.

Sigh. Kids these days.

All right, I'll skip to the disease. Trichomoniasis is a sexually transmitted disease encompassing a broad range of symptoms, with a very common asymptomatic carrier state. Annual incidence of trichomoniasis is over 170 million cases worldwide, eight million in North America, but perhaps half of infections in females and the vast majority of infections in males are asymptomatic and thus largely undiagnosed.

Women who are infected during pregnancy are more likely to have placental rupture, premature labor, and low-birth-weight babies. Trichomoniasis is also associated with cervical cancer and infertility. Perhaps most troubling of all is that T. vaginalis infection makes you more susceptible to HIV infection, probably because the increased concentration of white blood cells in the area in response to the protozoan provides more targets for HIV.

More generally, HIV susceptibility appears to be worsened by any existing STD, probably for the white blood cell reason. This has led to the hypothesis that the reason AIDS is such an apocalyptic disaster in Africa while remaining (relatively) well-controlled here is not because of any differences in condom usage or promiscuity but because of the relative prevalence of lesser "nuisance" STDs like trichomoniasis or chlamydia. This in turn raises the question of whether the most cost effective weapon we have in the fight against HIV might actually be antibiotics.