Pjm. Milligan et al., TRYPANOZOON - INFECTIVITY TO HUMANS IS LINKED TO REDUCED TRANSMISSIBILITY IN TSETSE .2. GENETIC MECHANISMS, Experimental parasitology, 81(3), 1995, pp. 409-415
Trypanozoon infections are less likely to mature in female tsetse than
in males. Analysis of maturation data from 37 trypanozoon isolates in
Glossina in. morsitans showed that while the proportion of mature inf
ections (salivary gland infections as a proportion of established midg
ut infections) varied from isolate to isolate, the proportion of matur
e infections in female flies was consistently smaller than the proport
ion in male flies. The log of the probability of maturation in females
is, on average, twice the log of the probability in males (estimate o
f 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 proportion
s 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 inf
ected bloodmeal and maturation) increases. The decrease is approximate
ly 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 obse
rvations which assumes that product(s) from an X-linked gene(s) kills
or otherwise prevents migrating parasites from establishing a mature i
nfection. Longer maturation times are associated with a heavy penalty
in terms of transmissibility as measured by the vectorial capacity. (C
) 1995 Academic Press, Inc.