Vector biology, broadly defined, is the science devoted to studying insects that transmit pathogens, their contact with humans, and their interaction with the disease-causing organisms. In the case of malaria, the vector is the anopheline mosquito and the disease-causing organism is the malaria parasite. Humans and anopheline mosquitoes are both considered to be the parasite's hosts.
One of the primary goals of vector biology in malaria research is to promote a better understanding of the disease cycle that will facilitate more effectively targeted control strategies. The vast majority of successful antimalaria campaigns have relied heavily on vector control.
The distribution of malaria within human populations is linked closely to site-specific characteristics of vector populations. Within any given area, there are usually fewer than five vector species, although the biology of each species is unique in many respects, including the sites where larvae develop, adult mosquito behavior (especially human-biting behavior), susceptibility to Plasmodium parasites, and the ability to transmit these parasites.
Not all mosquitoes can transmit human malarial parasites. Of the thousands of described mosquito species, only a fraction of those in the genus Anopheles serve as vectors. Some anopheline species do not feed on humans, others are not susceptible to human malaria parasites, and a number have life spans too short to allow the parasite to fully mature. Vector species that pose the greatest threat are abundant, long-lived, commonly feed on humans, and typically dwell in proximity to people. Their role in malaria transmission depends largely on the presence of a favorable environment for larval development and adult survival, and the ability to feed on humans. Transmission also depends significantly on human habits that promote host-vector contact.
Perhaps the least understood process in malaria transmission is the development of the parasite in the vector. To transmit malaria, vectors must be able to support parasite development through several key stages over 8 to 15 days. Only then are the sporozoite-stage parasites present and ready for transmission to new human hosts. Thus, from the standpoint of vector biology, there are three main points of attack for controlling malaria: the environment, human habits, and parasite development in the vector.
In cases in which the impact and feasibility of vector control are questioned, the result is often an overwhelming reliance on chemotherapy-based measures for reducing malaria-related mortality and morbidity. In countries with the most severe malaria problems, there are seldom funds for anything but antimalarial drugs and, in some cases, for limited vector control activities (mostly in urban areas). Such approaches usually do little