Well, neither the tsetse nor the trypanosome actually “walk” per se… Anyway…

A while back I posted a brief “howsyourmother” on a PLoS ONE article discussing the role of trypanosomes in an extinction event on Easter Island during the late 19th century. As it turns out, in 2007, also in PLoS ONE, an article was published discussing factors affecting the maturation of trypanosomes in a particular insect, the tsetse fly. You see, trypanosomes of various species undergo development inside of the tsetse prior to transmission, making the tsetse fly what biologists call a vector. So, understanding the development of these protozoa in the tsetse is particularly useful for those interested in infectious disease transmission. If it is possible to uncover the factors affecting trypanosome development inside the tsetse fly it may be possible to halt or disrupt the development, or so the logic goes.

As you can see in this wonderful diagram provided by the CDC, the transformation from bloodstream forms of trypanosomes to procyclic non-mammalian infective forms occurs in the midgut of the tsetse. To complete this life-cycle, however, they must migrate from the midgut to the salivary glands – only then will they transform into infective metacyclic forms that cause trypanosomiasis, or sleeping sickness. Based on previous research done in this area, the authors describe here the effects of antioxidants and environmental change on the life-cycle of one species in particular: Trypanosome brucei brucei.

They found that with the addition of L-cysteine, a naturally occurring amino acid, the maturation rates in both male and female tsetse are significantly increased, suggesting that this protein amino acid may be used by an enzyme as a substrate. On the opposite end of the spectrum, introduction of asorbic acid acted to significantly reduce maturation rates, while simultaneously increasing susceptibility to midgut infection. All in all, the authors found that it is highly likely trypanosomes require L-cysteine to make it from the midgut to the salivary glands. If it is possible to affect the levels of L-cysteine in the tsetse midgut at an epidemiological level, then it may be possible to significantly lower the prevelance of trypanosomiasis in Africa.

Environmentally, specifically to the trypanosome, it appears that while the infection does not affect the reproductive fitness of the fly, tsetse reproduction has a quite detrimental effect on maturation of trypanosomes. It is thought that this is so because reproduction will lower the available nutrients to the trypanosomes, by way of increasing competition between them and larval production.

So, while inhibiting L-cysteine production in the tsetse will likely prevent full maturation of the trypanosome, there are certainly other elements to the equation that have yet to be fully investigated.

Perhaps if the black rats simply had more sex there never would have been an extinction event in the first place…

(Related Video)

(References)

Macleod, E, Darby, A, Maudlin, I, Welburn, S, 2007, 'Factors Affecting Trypanosome Maturation in Tsetse Flies', PLoS ONE, 2 (2) 10.1371/journal.pone.0000239