Infective larvae of Brugia: escape from mosquitoes into water and subsequent oral infectivity in jirds

Distribution of Brugia malayi larvae and DNA in vector and non-vector mosquitoes: implications for molecular diagnostics

Background

The purpose of this study was to extend prior studies of molecular detection of Brugia malayi DNA in vector (Aedes aegypti- Liverpool) and non-vector (Culex pipiens) mosquitoes at different times after ingestion of infected blood.

Results

Parasite DNA was detected over a two week time course in 96% of pooled thoraces of vector mosquitoes. In contrast, parasite DNA was detected in only 24% of thorax pools from non-vectors; parasite DNA was detected in 56% of midgut pools and 47% of abdomen pools from non-vectors. Parasite DNA was detected in vectors in the head immediately after the blood meal and after 14 days. Parasite DNA was also detected in feces and excreta of the vector and non-vector mosquitoes which could potentially confound results obtained with field samples. However, co-housing experiments failed to demonstrate transfer of parasite DNA from infected to non-infected mosquitoes. Parasites were also visualized in mosquito tissues by immunohistololgy using an antibody to the recombinant filarial antigen Bm14. Parasite larvae were detected consistently after mf ingestion in Ae. aegypti- Liverpool. Infectious L3s were seen in the head, thorax and abdomen of vector mosquitoes 14 days after Mf ingestion. In contrast, parasites were only detected by histology shortly after the blood meal in Cx. pipiens, and these were not labeled by the antibody.

Conclusion

This study provides new information on the distribution of filarial parasites and parasite DNA in vector and non-vector mosquitoes. This information should be useful for those involved in designing and interpreting molecular xenomonitoring studies.

The non-specific nature of the response of mosquito flight muscle to filarial parasitization

The significance of the histological changes induced by filarial larvae in the indirect flight muscle fibres of susceptible female mosquitoes was investigated by inflicting mechanical (needle-puncture) injury on thoracic tissues of male and female mosquitoes of various species. Mechanical injury caused the flight muscle of all mosquitoes, irrespective of species, sex or filarial susceptibility, to react in the same way as that of filaria-infected, susceptible females; other thoracic tissues responded in a similar fashion. Since these responses are closely akin to those observed by earlier authors in various tissues of other insects subjected to experimental trauma, it seems reasonable to regard the reactions of indirect flight muscle of mosquitoes to filarial larvae as an example of a common, non-specific response by insects to a range of traumatic stimuli.