Nina Monica Simon - OPUS - Universität Würzburg

________________________________________________________________Introduction
1.6 The malaria parasite and the human complement in the mosquito
midgut
1.6.1 Sexual reproduction of malaria parasites in the mosquito midgut
Malaria parasites are taken up by the mosquito in form of sexual precursor cells, the
intraerythrocytic gametocytes (reviewed in Pradel, 2007 and Kuehn and Pradel, 2010).
After the ingestion into the mosquito’s midgut the malaria parasite has not only to
survive, it has to reproduce sexually in the aggressive environment of the mosquito
midgut. Triggered by external stimuli in the mosquito midgut, gametocytes egress
from the enveloping host erythrocyte and form gametes. During this process the
surrounding and protecting parasite membranes rupture (Sologub et al., 2011). Within
approximately 20 min, fertile gametes have formed and fertilization occurs within one
hour post-blood meal. The mosquito midgut contains digestive enzymes, midgut
bacteria and furthermore, antibodies, immune cells, and human complement factors
which were taken up together with the blood meal (see Fig. 1.13). Previous studies on
P. berghei describe that during the first three hours of development in culture, 30-50 %
of mosquito midgut stages survive complement exposure. Subsequently, parasites
become increasingly sensitive to complement mediated lysis (Margos et al., 2001).
Initial studies on complement effects on the infectivity of malaria parasites were
conducted with P. gallinaceum, the malaria parasite which infects birds. The ability of
gametocytes to infect mosquitoes in the presence of native human serum has been
previously been attributed to proteases that inactivate the human complement system
before the gametes and zygotes emerge as extracellular parasites in the blood meal
(Grotendorst et al., 1986).
Figure 1.13: The malaria parasite in the mosquito midgut is surrounded by mosquito midgut factors
and human blood meal contents.
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