Haematophagy and Opportunities for Symbiotic Control of Insect Vectors of Human Protozoan Diseases

Insect vector-symbiotic relationships are widely reported in literature with several microorganisms reported to play a key role in growth, development, survival and evolutionary success of insect disease vectors. Symbiotic bacteria are prevalent in insects like mosquitoes, sand flies, tsetse flies that are known efficient vectors of tropical diseases. Several studies have been undertaken to determine the mechanisms of the insect host-symbiotic relationships with the aim of developing new strategies to control human vector borne diseases. Some bacterial symbionts have evolved together with the respective insect hosts such that the hosts cannot survive without them. This is the basis of an intervention strategy known as symbiotic control. It is a recent multi-pronged approach that targets symbiotic microorganisms to control insect disease vectors and possibly interfere with their vectorial capacity. The strategy is promising and has recently generated a lot of research interest. Three such approaches have been reported and are: the interference and destabilization of microbial symbionts essential for insect vector survival; changing the genetic make-up of symbionts so that they generate and express anti-parasite agents within the insect host; and the introduction of other microorganisms that may eventually negatively affect the longevity and vector competence of the offspring in future populations. The availability of new molecular techniques has made the understanding of symbiotic relationships more clear. With sustained and increasing research interest and recent findings in insect-symbiotic associations, there is high possibility that soon we will have many insect-vector control programs utilizing this information and techniques. In this review we highlight the evolution of blood feeding behavior in insect disease vectors, new findings and developments on microbial symbiosis in mosquitoes, sand flies, triatomine bugs and tsetse flies that are feasible and therefore form basis for formulating symbiotic control strategies for major human insect borne parasitic protozoan diseases: malaria, leishmaniasis and trypanosomiasis.