Imaging mosquito transmission of Plasmodium sporozoites into the mammalian host: immunological implications.

The malaria infection is initiated in mammals by injection of the sporozoite stage of the parasite through the bite of Plasmodium-infected, female Anopheles mosquitoes. Sporozoites are injected into extravascular portions of the skin while the mosquito is probing for a blood source. Sporozoite gliding motility allows them to locate and penetrate blood vessels of the dermis or subcutaneous tissues; once in the blood, they reach the liver, within which they continue their development.

Intradermal immunization of mice with radiation-attenuated sporozoites of Plasmodium yoelii induces effective protective immunity.

Background: Intravenous injection of mice with attenuated Plasmodium berghei sporozoites induces sterile immunity to challenge with viable sporozoites. Non-intravenous routes have been reported to yield poor immunity. Because intravenous immunization has been considered to be unacceptable for large scale vaccination of humans, assessment was made of the results of intradermal immunization of mice with Plasmodium yoelii, a rodent malaria parasite whose infectivity resembles that of human malaria.

Neither mosquito saliva nor immunity to saliva has a detectable effect on the infectivity of Plasmodium sporozoites injected into mice.

Malaria infection is initiated when a female Anopheles mosquito probing for blood injects saliva, together with sporozoites, into the skin of its mammalian host. Prior studies had suggested that saliva may enhance sporozoite infectivity. Using rodent malaria models (Plasmodium berghei and P.