Abstract
BackgroundThe 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.ResultsParasite 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.ConclusionThis 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.
Highlights
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
These studies allowed us to assess the potential value of tissue specific assays to estimate the prevalence of infective-stage larvae in mosquitoes; we investigated the issue of direct mosquito to mosquito transfer of parasite DNA that could confound molecular xenomonitoring (MX) studies
In Ae. aegypti-LVP, 73.6% of the recovered B. malayi mf at 2 h post ingestion (PI) had successfully penetrated the midgut, with 49.4% located in the thorax
Summary
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. Human lymphatic filiarasis (LF) is caused by the mosquito-borne filarial nematodes Wuchereria bancrofti, Brugia malayi, and B. timori These parasites are currently targeted for elimination by the Global Program for the Elimination of Lymphatic Filariasis (GPELF), and workers in this program have reported both achievements and future challenges to eliminating parasite transmission in endemic areas [1,2,3]. There are several factors that should be carefully considered when using molecular techniques to investigate parasites within the mosquito intermediate host, including the (1) various life cycle stages and their tissue locations, (2) likelihood of parasite development to the infective stage, i.e., vector competence, and (3) limitations of the particular detection assay, i.e., ability to distinguish infection stages and living from dead parasites. Anopheles spp. have been divided into two body regions (head/thorax and abdomen) to provide better estimates of mosquitoes infected with Plasmodium sporozoites and/or pre-sporozoite stages [15,16,17] and the heads of blackflies have been removed (by mass dissection techniques) for the restricted, head-only, PCR assays targeting Onchocerca DNA, which is more likely to provide a better estimate of infective-stage parasites because other developmental stages generally reside outside of the head [18,19]
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