mission intensity, derived from measurements of vector densities and sporozoite rates (analogous to the EIR), can provide useful information about patterns of endemicity in human populations. For the purposes of malaria management, it is useful to know whether individuals receive 5, 50, or 500 infective bites per year, as well as when the transmission occurs. Vector-derived EIR estimates are highly correlated with measurements of malaria incidence. In this respect, EIRs provide stronger predictive capabilities than do estimates of prevalence.

Analysis of fresh blood meals of human-fed anophelines for the presence of antimalarial antibodies represents a possible alternative approach to serosurveys. Human antiparasite antibodies remain intact, undigested, for about 24 hours. Even though anophelines ingest only 1 to 2 microliters of blood, stage-specific antibodies can be detected by simple immunoassays (Beier et al., 1989). Although molecular probes do not appear to be sensitive enough to detect the presence of parasites in this small volume of blood, polymerase chain reaction methods could be used in the future to detect low numbers of parasites in mosquito blood meals. If sufficient epidemiologic information can be extracted from analyzing the blood meals of mosquitoes, there may be less need to draw blood from residents of endemic communities. As a replacement for traditional surveys, then, the effectiveness of such an approach deserves consideration.

Entomological Components of Malaria Vaccine Development

The development and testing of P. falciparum sporozoite vaccines depend on the availability of sporozoites from experimentally infected mosquitoes. Sporozoites are in great demand for use in antibody assays and in the characterization and evaluation of candidate vaccines. Studies testing the efficacy of vaccines against sporozoite challenge have used infective mosquitoes to feed on volunteers.

This methodology raises a number of vector-related questions. For example, since the number of sporozoites transmitted by infective mosquitoes is unknown, vaccines are being tested without reference to levels of sporozoite inocula. There is also the concern that laboratory infected mosquitoes may have a greater sporozoite transmission potential than do those in nature, since sporozoite loads are generally 10 to 200 times higher in the former (Davis et al., 1989). These entomological concerns are of equal importance when one is testing vaccines against blood stages of the malaria parasites.

Vector-related issues will become even more important as vaccines move from laboratory testing to field evaluation. Some of the concerns have already been outlined (World Health Organization, 1986). A prerequisite for vaccine field trials is the long-term characterization of malaria transmis-



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