A critical appraisal of molecular xenomonitoring as a tool for assessing progress toward elimination of Lymphatic Filariasis

Abstract

We used molecular xenomonitoring (MX, detection of filarial DNA in mosquitoes) to evaluate the impact of mass drug administration (MDA) in sentinel locations in Egypt with high (11.5%) and low (4.1%) baseline microfilaria prevalence rates. Blood-fed Culex pipiens were pooled by household and tested for Wuchereria bancrofti DNA by PCR. There was no significant relationship between the infection status of household residents and parasite DNA status of mosquitoes from the same houses. After 5 MDA rounds, parasite DNA rates in mosquitoes in high- and low-prevalence areas were reduced by 93.8% and 100% to 0.19% (95% CI: 0.076-0.382%) and 0% (95% CI: 0-0.045%), respectively. These changes were consistent with decreases in microfilaria prevalence rates in these sites; they provide insight regarding the minimal mosquito DNA rates necessary for sustained transmission of filariasis in Egypt. We conclude that MX is a powerful tool for monitoring the impact of MDA on filariasis endemicity and transmission.

Figure 1

Map of Tahoria village in the Qal study area, showing households where mosquitoes were collected for PCR testing prior to the first round of mass drug administration (MDA): ▲, houses with mosquitoes positive for filarial DNA by PCR; △, houses with mosquitoes negative for filarial DNA by PCR; housing blocks are shown as squares; dashed lines represent irrigation and drainage canals.

Figure 2

Effect of mosquito sample size on the percentage of houses with Wuchereria bancrofti DNA in Culex pipiens in the Giz (A) and Qal (B) study areas. Histograms show results obtained before the first round of mass drug administration (MDA) and after each round of MDA.

Figure 3

Frequency distributions for the number of houses with different numbers of gravid or blood-fed Culex pipiens captured before treatment in the Giz (A) and Qal (B) study areas.

Figure 4

Impact of mass drug administration on the percent of houses with Wuchereria bancrofti DNA in Culex pipiens in the Giz (gray bars) and Qal (black bars) study areas. Data are shown for households with mosquito pool sizes ≥ 5; error bars show 95% confidence limits.