Study of the distribution of circumsporozoite antigen in Anopheles gambiae infected with Plasmodium falciparum, using the enzyme-linked immunosorbent assay.

Anopheles gambiae, experimentally infected with Plasmodium falciparum, were dissected 14 days later for microscopical detection of sporozoites and oocysts. The head, salivary glands, thorax, midgut, legs, ovaries, Malpighian tubules, the remainder of the abdominal tissues and the dissection fluid of each mosquito were examined by a two-site enzyme-linked immunosorbent assay (ELISA) for the detection and quantification of circumsporozoite antigen (CS ag). 19 mosquitoes had CS ag in at least one of the specimens examined. Very large individual variability was observed in the presence and/or quantity of CS ag in the various parts. 7 mosquitoes were ELISA-positive in all 9 specimens; the salivary glands and thorax contained most CS ag, whereas the Malpighian tubules and ovaries contained the least; all the thoraces contained CS ag, even that of one mosquito of which the salivary glands lacked both sporozoites and CS ag; of 17 ELISA-positive salivary glands, 15 were found to contain sporozoites. The existence of free antigen associated with sporozoites, and the limitations of the ELISA technique in demonstrating the infectivity of a malaria vector, are discussed.