Increased intradermal probing time in sporozoite-infected mosquitoes.

Because malaria sporozoites destroy segments of the salivary glands of vector mosquitoes, we determined whether salivary function is impaired. Such pathology would result in a prolonged intradermal probing phase of feeding behavior, because the role of saliva is to help locate blood vessels. Indeed, non-infected Aedes aegypti mosquitoes probed for a shorter period than did either sporozoite-infected or saliva-deprived mosquitoes. Salivary apyrase activity is reduced to a third following maturation of sporozoites. Apyrase activity, normally, is confined to those regions invaded by sporozoites. Sporozoite-infected and non-infected mosquitoes produced equal volumes of saliva. We conclude that sporozoite infection impairs the vector's ability to locate blood vessels by affecting the quality of salivary product, thereby increasing potentially infective host contacts.