Plasmodium falciparum and P. berghei: detection of sporozoites and the circumsporozoite proteins in the saliva of Anopheles stephensi mosquitoes.

Sporozoites and free circumsporozoite (CS) protein were stained immunoenzymatically in 1-min saliva samples collected from Anopheles stephensi mosquitoes infected with either Plasmodium berghei or P. falciparum. The number of sporozoites in 1-min saliva-streak samples significantly increased as the salivary gland index rose from 3+ to 4+. For P. berghei-infected mosquitoes from which saliva had been collected before 30 days postfeed, the median sporozoite counts for 3+ and 4+ gland indexes were 4.5 and 116, respectively. For P. falciparum-infected mosquitoes, the median counts obtained in two experiments were 4.5 and 14.5 (3+) and 97 and 107 (4+), respectively. The frequency of sporozoite detection in the saliva of mosquitoes containing < 100 salivary-gland sporozoites was low (0.1), whereas that in the saliva of mosquitoes with > 100 sporozoites was high (0.96). In highly infected 4+ P. berghei-infected mosquitoes from which saliva had been collected after 30 days postinfection, both the volume of saliva collected and the median number of sporozoites recovered decreased significantly.