Biology and biochemistry of sexual and sporogenic stages of Plasmodium falciparum: a review.

Abstract

Gametocyte development has been studied in synchronous cultures of P. falciparum. These studies have confirmed that maturation of this stage occurs over 7 days and doubling of the DNA content takes place early in the development stage. There appears to be no direct relationship between the number of gametocytes ingested by a mosquito and the oocyst load, nor between the latter and the number of salivary gland sporozoites. The variability in oocyst load could in part be explained by the individual differences in digestion speed of mosquitoes. The number of salivary gland sporozoites and thus also that of sporozoites inoculated per bite of a mosquito is influenced by the number of blood meals which the mosquito has ingested after the infectious blood meal. Moreover, the longer the mosquito survives the more infective it becomes due to increased density of sporozoites in the glands. Anti-sporozoite antibodies present in the blood meal of an already infected mosquito do not hinder migration of sporozoites to the salivary glands. It has been demonstrated that monoclonal antibodies directed against epitopes of gamete surface proteins of molecular weight of 230, 45/48 and 25 kDa could block sporogony. Transmission blocking antibodies are also present in the sera of individuals exposed to natural transmission. These epitopes of the target proteins are non-repetitive and conformational and thus rendered non-reactive by reduction. Moreover, some of these surface proteins are glycosylated and/or acylated, and may depend on the presence of the native disulphide bonds for the preservation of immune reactivity. These post-translational modifications have made screening of gene libraries with immunoproteins difficult.(ABSTRACT TRUNCATED AT 250 WORDS)