Trypanozoon infections are less likely to mature in female tsetse than in males. Analysis of maturation data from 37 trypanozoon isolates in Glossina m. morsitans showed that while the proportion of mature infections (salivary gland infections as a proportion of established midgut infections) varied from isolate to isolate, the proportion of mature infections in female flies was consistently smaller than the proportion in male flies. The log of the probability of maturation in females is, on average, twice the log of the probability in males (estimate of the ratio of the logged proportions is 2.09, 95% confidence interval (CI) 1.8 to 2.5). Human serum-resistant isolates were less likely to mature than human serum-sensitive isolates (ratio of logged proportions maturing was 1.5, 95% CI 1.3 to 1.8, in both male and female tsetse). Data for four other trypanosome stocks show that the probability of maturation decreases as the maturation time (the delay between the infected bloodmeal and maturation) increases. The decrease is approximately exponential with twice the half-life in male flies compared to that in female flies (estimate of the ratio of the exponential parameters is 1.97, 95% Cl 0.7 to 3.3). A model is proposed to explain these observations which assumes that product(s) from an X-linked gene(s) kills or otherwise prevents migrating parasites from establishing a mature infection. Longer maturation times are associated with a heavy penalty in terms of transmissibility as measured by the vectorial capacity.
Milligan, P.J.M.; Maudlin, I.; Welburn, S.C. Trypanozoon: Infectivity to Humans Is Linked to Reduced Transmissibility in Tsetse. Experimental Parasitology (1995) 81 (3) 409-415. [DOI: 10.1006/expr.1995.1132]