Plasmodium berghei: mechanisms and sites of resistance to sporogonic development in different mosquitoes

An experimental study of the mechanisms and patterns of resistance to Plasmodium berghei in different mosquito species revealed a diversity of factors which prevent or inhibit sporogonic development in its different phases and in different sites in the mosquito vector. The experiments showed that Culex salinarius was a totally resistant species in which exflagellation and ookinete formation are prevented. In Aedes aegypti, ookinetes in small or moderate numbers are formed but penetration of the mosquito midgut wall is blocked and oocysts are not formed. In the three experimental vectors, Anopheles quadrimaculatus, Anopheles aztecus, and Anopheles stephensi grades of enhanced susceptibility are recognized. They are expressed in lesser numbers of abnormal and degenerative oocysts, in higher numbers of sporozoites in the salivary gland, and greater viability and invasiveness of these sporozoites. In Anopheles dureni, the natural vector of rodent malaria, one observes both in nature and under experimental conditions the highest adaptation and most pronounced grade of susceptibility to P. berghei.