| dc.description.abstract | Transmission of trypanosomes (Genus Trypanosoma) by tsetse flies (Genus Glossina) is a process influenced by several factors. Such factors may arise from the trypanosomes, tsetse flies, hosts upon which flies feed and environmental conditions such as temperature. Investigations of these variables have a direct bearing on tsetse/trypanosomiasis control measures as well as providing information on the disease situation. In this study, three factors were investigated under laboratory conditions; these comprised age, sex and period of starvation of G.M morsitans on the effect of uptake and development of Trypanosoma congolense and T. congolensej T.b. brucei mixed infections.
In the first study to investigate fly age, sex and period
of starvation on the development of T. congolense, a total of
5 groups of flies were used comprising 1,739 specimens.
Following infection with. congolense all flies were maintained
on rabbits for a period of 30 days before each was dissected
and the infection assessed.
Mature trypanosome infections were highest in 16 hour
old and 2 day old (48 hours starved) flies, neither of which
had previously had a blood meal. The other groups comprising
2 day old fed flies, 7 day old fed flies and 7 day old (48 hours
starved) flies, had significantly lower infection levels and,
furthermore, did not differ significantly (P > 0.05) from each
other. within both day old: fly groups, the group starved for
48 hours had significantly higher levels of infection than the
group which had been allowed to feed on rabbits prior to
infection. Additionally, within the two 7 day old fly groups,
a period of 48 hours starvation did not produce any
enhancement of infection levels over the non-starved group which
were maintained on rabbit blood for 5 days prior to infection.
The results indicate that the age of the fly alone, is not a
significant factor cont rolling the level of trypanosome infections.
Rather, it may be concluded that trypanosome infections are elevated significantly when the first blood meal that an adult fly receives, is an infective one. From this laboratory derived
data it could therefore be postulated that in the field situation, young flies which take their first blood meals from
an infected host animal, are most likely to have the highest
levels of trypanosome infection in the case of T. congolense
and this species of vector.
A sex-linked factor was also noted in this study in that
immature infections were most frequently recorded in female
flies whilst males displayed a preponderance of mature
infections. Whether trypanosome maturation is inhibited in
females or enhanced in males, remains unknown.
In the second study, to determine the effect of mixed
trypanosome T. congolense/T.b. brucei) infections on levels
of infection rates in flies, 5 groups of flies were again
employee comprising 571 specimens. Following maintenance of
flies on rabbits for a period of 30 days, infected fly organs were inoculated into Swiss mice to determine the species of
trypanosomes. One out of 46 (2.2%) males of the flies that
fed on a mixed trypanosome infected mea 1 developed double
mature infections of T. congolense and T.b.brucei. It seems
possible that even under natural conditions a single fly can
transmit such mixed infections to a susceptible host.
Labral infections in the group of flies that fed on only
T. congolense infected meal through the silicone membrane
were observed in 5 out of 51 (11.8%) males and 5 out of 59
(8.5%) females. These infection levels were statistically
comparable to labral infections in the group of flies that
fed on mixed T. congolense/T.b. brucei infected meal for
which results were, 4 out of 46 (8.7%) males and 10 out of
71 (14.1%) females. The latter group, however, showed. significantly lower (X2 = 6.4, p < 0.05) hypopharyngeal infections in females, 2 out of 71 (2.8%) than the former group, 9 out of 59 (15.3%), respectively. Similar comparisons of mature infections between groups that had fed on T.b. brucei infected meal alone and on mixed infections did not
reveal any significant differences. It seems that within the fly system, development of T. congolense might be inhibited by T.b.brucei in experimentally infected flies.
Defibrination of infected blood for silicone membrane feeding lowered salivary slana infections in the case of T.b. brucei as compared to a control group that fed directly on the same donor rats. This was not the case for T. congolense infections in which infections in flies that fed through the membrane did not differ significantly with a
control group of flies that fed directly on infected rats | |
