No abstract

We developed and evaluated real-time polymerase chain reaction (PCR) assays for detecting Wuchereria bancrofti DNA in human blood and in mosquitoes. An assay based on detection of the W. bancrofti "LDR" repeat DNA sequence was more sensitive than an assay for Wolbachia 16S rDNA. The LDR-based assay was sensitive for detecting microfilarial DNA on dried membrane filters or on filter paper. We also compared real-time PCR with conventional PCR (C-PCR) for detecting W. bancrofti DNA in mosquito samples collected in endemic areas in Egypt and Papua New Guinea. Although the two methods had comparable sensitivity for detecting filarial DNA in reference samples, real-time PCR was more sensitive than C-PCR in practice with field samples. Other advantages of real-time PCR include its high-throughput capacity and decreased risk of cross-contamination between test samples. We believe that real-time PCR has great potential as a tool for monitoring progress in large-scale filariasis elimination programs.

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.

Abstract. We studied effects of compliance on the impact of mass drug administration (MDA) with diethylcarbamazine and albendazole for lymphatic filariasis (LF) in an Egyptian village. Baseline microfilaremia (mf) and filarial antigenemia rates were 11.5% and 19.0%, respectively. The MDA compliance rates were excellent (> 85%). However, individual compliance was highly variable; 7.4% of those surveyed after five rounds of MDA denied having ever taken the medications and 52.4% reported that they had taken all five doses. The mf and antigenemia rates were 0.2% and 2.7% in those who reported five doses of MDA and 8.3% and 13.8% in those who reported zero doses. There was no significant difference in residual infection rates among those who had taken two or more doses. These results underscore the importance of compliance for LF elimination programs based on MDA and suggest that two ingested doses of MDA are as effective as five doses for reducing filariasis infection rates.

PCR has recently been studied as a promising tool for monitoring the progress of efforts to eliminate lymphatic filariasis. PCR can be used to test concurrently at least 30 pools, with as many as 40 mosquitoes in each pool, for the presence of filarial larvae. The SspI PCR assay for the detection of Wuchereria bancrofti DNA in pools of mosquitoes has been used since 1994 in a variety of laboratories worldwide. During that time, the original assay has been modified in these different laboratories and no standardized assay currently exists. In an effort to standardize and improve the assay, a meeting was held on 15-16 November 2001, at Emory University in Atlanta, with representatives from most of the laboratories currently using the assay. The first round of testing was designed to test the four most promising methods for DNA extraction from pools of mosquitoes. Two of the four methods stood out as clearly the best and these will be now optimised and evaluated in two further rounds of testing.