Comparative Susceptibility of Different Biological Forms of Anopheles stephensi to Plasmodium berghei ANKA Strain

There are varying degrees of compatibility between malaria parasite-mosquito species, and understanding
this compatibility may be crucial for developing effective transmission-blocking vaccines. This study investigates the
compatibility of different biological forms of a malaria vector, Anopheles stephensi, to Plasmodium berghei ANKA strain.
Methods: Several biologically different and allopatric forms of A. stephensi were studied. Three forms were isolated from
different regions of southern Iran: the variety mysorensis, the intermediate form and the native type form, and an additional
type form originated from India (Beech strain).The mosquitoes were experimentally infected with P. berghei to compare
their susceptibility to parasitism. Anti-mosquito midgut antiserum was then raised in BALB/cs mice immunized against gut
antigens from the most susceptible form of A. stephensi (Beech strain), and the efficacy of the antiserum was assessed in
transmission-blocking assays conducted on the least susceptible mosquito biological form.
Results: The susceptibility of different biological forms of A. stephensi mosquito to P. berghei was specifically inter-type
varied. The Beech strain and the intermediate form were both highly susceptible to infection, with higher oocyst and
sporozoite infection rates than intermediate and mysorensis forms. The oocyst infection, and particularly sporozite infection,
was lowest in the mysorensis strain. Antiserum raised against midgut proteins of the Indian Beech type form blocked
infection in this mosquito population, but it was ineffective at blocking both oocyst and sporozoite development in the
permissive but geographically distant intermediate form mosquitoes. This suggests that a strong degree of incompatibility
exists between the mosquito strains in terms of midgut protein(s) acting as putative ookinete receptors.
Conclusions: The incompatibility in the midgut protein profiles between two biological forms of A. stephensi demonstrates
a well-differentiated population structure according to geographical origin. Therefore, the design of potential transmissionblocking
strategies should incorporate a more thorough understanding of intra-species variations in host-parasite
interactions.