1989 Master's thesis, Fakultät für Biologie der Universität Tübingen, Germany
Institute of Tropical
Medicine, University of Tübingen, Germany
Martin Eichner
1989
Master's thesis, Fakultät für Biologie der Universität Tübingen,
Germany
Institute of Tropical
Medicine, University of Tübingen, Germany
After a fly's blood meal or injection the larvae needed the same time
for development. The earliest third stage larvae (L
appeared six days
post infectionem
(pi). The development was finished
nine days pi.
After nine days pi 30 % of the injected microfilariae (mff) had developed
to third stage larvae, irrespective of vector species or size. But the
flies from the breeding sites Bile and Nyoke (
S. squamosum
) gave
rise to only 13 % L
/mff.
Maybe they form to some extent a refractary subpopulation.
The frequency distribution of flies with n larvae (
injection dose) didn't fit to a binomial distribution, which was expected
for a constant portion of 30 % microfilariae being in the physiological
state for development.
It was not possible to influence the success of injection systematically by haemolymph transmissions.
Injected microfilariae of the forest strain developed as well as those of the savanna strain. In contrast to blood meal infections the forest strain developed well in the savanna flies ( S. sirbanum, S. damnosum s. str. ). Consequently the peritrophic membrane and the penetration of the gut wall are the main reasons of the missing development after a blood meal.
In male flies microfilariae can also develop to infective larvae. Injected as well as non-injected male flies had a shorter life expectancy than females.
S. bovis
, which frequently feeds on man, is able to develop microfilariae
to the infective stage and might therefore be a vector of onchocerciasis.
Although
S. hargreavesi
doesn't feed on man,
O. volvulus
developed better in this fly (37 % L
/mff)
than in
S. damnosum. s. l.
. In
S. kenyae
the development
stopped at the second stage.
The infective larvae of the savanna strain were significantly longer (663 µm) than those of the forest strain (624 µm). The strains may be distinguished by this feature.
The length of the infective larvae wasn't influenced by the age pi, the localization (in head, thorax and abdomen), the vector species and size, the number of larvae per fly (forest strain) and the thoracic volume per larva. Within the savanna strain the length stages increases with the number of larvae per fly. The lengths of the larvae developing in one fly had a variance, which was smaller than expected. This suggests an influence of the fly or a mutual effect of the larvae.
The non-injected flies survived up to 39 days, while injected ones didn't
live longer than 29 days pi. In the beginning they had a roughly constant
mortality (5 - 12 % per day), which increased at the time of the appearence
of third stage larvae. The whole survivorship curves were approximated
by Gompertz curves.