Molecular and biochemical factors influencing vector competence in mosquito-borne filariasis

Efforts to control mosquito-borne diseases based on traditional control strategies are problematic. Therefore, novel control strategies, which incorporate vector resistance or refractory mechanisms to prevent parasite development, are being designed to stop disease transmission by mosquitoes. Resistance mechanisms are active immune responses, like melanotic encapsulation, that are directed against the pathogen, while refractory mechanisms prevent parasite development due to a physiological or biochemical incompatibility.; Because previous studies reported the increased expression of an 84-kDa polypeptide in Aedes aegypti mosquitoes that were melanotically encapsulating filarial worms, the present work was designed to begin characterization of this 84-kDa polypeptide. Sequence analysis of protein microsequence data did not provide conclusive data regarding this polypeptide's identity. However, using mosquito genomic DNA and degenerate oligonucleotide primers, designed from the microsequence data, a PCR-generated clone was obtained. A 540-bp cDNA clone then was isolated by screening a mosquito library with the PCR-generated clone. Northern blot hybridization revealed a 2.0-kb message that is up-regulated in immune-activated mosquitoes. DNA sequence analysis of this 540-bp clone did not reveal the identity or the role the 84-kDa polypeptide might play during melanotic encapsulation reactions.; The mechanism responsible for increased parasite intensity in a strain of A. aegypti selected for susceptibility to the filarial worm, B. malayi also was investigated. Experiments assessing midgut penetration in this susceptible strain and a refractory strain selected from the same parental stock show that significantly greater numbers of microfilariae are ingested and then penetrate the midgut of susceptible mosquitoes compared to refractory mosquitoes. The genetic basis for these differences was assessed using restriction fragment length polymorphism markers (RFLP) and quantitative trait loci (QTL) mapping. This mapping identified a QTL on chromosome 2, idb (2,LF181), that seems to influence ingestion ability. This QTL is linked to a previously identified QTL for susceptibility to B. malayi, fsb (2,LF98), as well as to loci for susceptibility to the malaria parasite, Plasmodium gallinaceum, and yellow fever virus. These results suggest that this region of chromosome 2 contains one or more genes that influence susceptibility to several mosquito transmitted pathogens.