Molecular xenomonitoring for Wuchereria bancrofti in Culex quinquefasciatus in two districts in Bangladesh supports transmission assessment survey findings.

BACKGROUND: Careful monitoring for recrudescence of Wuchereria bancrofti infection is necessary in communities where mass drug administration (MDA) for the elimination of lymphatic filariasis (LF) as a public health problem has been stopped. During the post-MDA period, transmission assessment surveys (TAS) are recommended by the World Health Organization to monitor the presence of the parasite in humans. Molecular xenomonitoring (MX), a method by which parasite infection in the mosquito population is monitored, has also been proposed as a sensitive method to determine whether the parasite is still present in the human population. The aim of this study was to conduct an MX evaluation in two areas of Bangladesh, one previously endemic district that had stopped MDA (Panchagarh), and part of a non-endemic district (Gaibandha) that borders the district where transmission was most recently recorded. METHODOLOGY/PRINCIPAL FINDINGS: Mosquitoes were systematically collected from 180 trap sites per district and mosquito pools were tested for W. bancrofti using real-time PCR. A total of 23,436 intact mosquitoes, representing 31 species, were collected from the two districts, of which 10,344 (41%) were Culex quinquefasciatus, the vector of W. bancrofti in Bangladesh. All of the 594 pools of Cx. quinquefasciatus tested by real-time PCR were negative for the presence of W. bancrofti DNA. CONCLUSIONS/SIGNIFICANCE: This study suggested the absence of W. bancrofti in these districts. MX could be a sensitive tool to confirm interruption of LF transmission in areas considered at higher risk of recrudescence, particularly in countries like Bangladesh where entomological and laboratory capacity to perform MX is available.

Fitness cost of Litomosoides sigmodontis filarial infection in mite vectors; implications of infected haematophagous arthropod excretory products in host-vector interactions.

Filariae are a leading cause of infections which are responsible for serious dermatological, ocular, and vascular lesions. Infective third stage larvae (L3) are transmitted through the bite of a haematophagous vector. Litomosoides sigmodontis is a well-established model of filariasis in the mouse, with the vector being the mite Ornithonyssus bacoti. The aim of the study was to analyse the filarial infection in mites to determine the consequences of filarial infection in the blood-feeding and the reproduction of mites as well as in the regulation of vector-induced inflammation in the mouse skin. Firstly, L3 are unevenly distributed throughout the host population and the majority of the population harbours a moderate infection (1 to 6 L3). Filarial infection does not significantly affect the probing delay for blood feeding. The number of released protonymphs is lower in infected mites but is not correlated with the L3 burden. Finally, induced excreted proteins from infected mites but not from uninfected mites stimulate TNF- α and the neutrophil-chemoattractant KC production by antigen-presenting cells (APCs). Altogether, these results describe the modification of the mite behavior under filarial infection and suggest that the immunomodulatory capacity of the mite may be modified by the presence of the parasite, hindering its defensive ability towards the vertebrate host.

Field evaluation of an insect growth regulator, pyriproxyfen 0.5% GR against Culex quinquefasciatus, the vector of Bancroftian filariasis in Pondicherry, India.

Pyriproxyfen, 0.5% granular formulation (GR), an insect growth regulator (IGR) was tested against Culex quinquefasciatus larvae and pupae in disused wells, cesspits and drains at the dosages of 0.1, 0.25, and 0.5kg(ai)/ha to determine the most appropriate field dosage. The IGR was found to be effective against C. quinquefasciatus larvae and pupae in all the larval habitats tested. In drains with slow moving water, application of pyriproxyfen 0.5% GR at 0.5kg(ai)/ha resulted in >80% emergence inhibition (EI) of adults for 4 weeks. At 0.1 and 0.25kg(ai)/ha, the EI was always less than 80%. In stagnant drains, the IGR yielded >80% EI for 1-week period at 0.1kg(ai)/ha. At 0.25 and 0.5kg(ai)/ha, the efficacy was 5-10 times higher. In cesspits, the EI was >80% for 6 weeks when pyriproxyfen 0.5% GR was applied at 0.1kg(ai)/ha, for 11 weeks at 0.25kg(ai)/ha and 9 weeks at 0.5kg(ai)/ha. In disused wells treated at the dosage 0.1kg(ai)/ha, there was >80% EI for 15 weeks and at 0.25 and 0.5kg(ai)/ha, the effective duration was about 1.6-1.8 times longer (24-28 weeks). Considering the quantum of IGR required and the cost and also for safety reasons, the low dosage 0.1kg(ai)/ha is recommended as the field dosage to be applied at weekly interval in stagnant drains, 6 weeks interval in cesspits and 15 weeks interval in disused wells. Since pyriproxyfen 0.5% GR has a relatively longer residual effect than the other IGRs the operational cost could be minimized. Pyriproxyfen 0.5% GR could be one of the choices in the chemical control strategy in Integrated Vector Control Programmes.

Effect of yearly mass drug administration with diethylcarbamazine and albendazole on bancroftian filariasis in Egypt: a comprehensive assessment.

BACKGROUND: Egypt was one of the first countries to implement a national programme to eliminate lymphatic filariasis based on WHO's strategy of repeated rounds of mass drug administration (MDA) with diethylcarbamazine and albendazole (target population, 2.5 million in 181 localities). We assessed the effect of five yearly rounds of MDA on filariasis in four sentinel villages in Egypt. METHODS: We studied two areas with different infection rates before MDA: the Qalubyia study area had a low infection rate because of previous treatment with diethylcarbamazine; this was typical of most filariasis-endemic villages in Egypt before MDA. The Giza study area had a high baseline infection rate. We undertook repeated surveys in villages for treatment compliance and tests for microfilaraemia and circulating filarial antigenaemia, antibodies to filarial antigen Bm14 in schoolchildren, and infections in indoor-resting mosquitoes (assessed by PCR). FINDINGS: MDA compliance rates were excellent (>80%). In Giza after MDA, prevalence rates of microfilaraemia and circulating filarial antigenaemia fell from 11.5% to 1.2%, and from 19.0% to 4.8%, respectively (p<0.0001). Corresponding rates in Qalubyia fell from 3.1% to 0% and 13.6% to 3.1%, respectively (p<0.0001). Rates of antifilarial antibody and circulating filarial antigenaemia in schoolchildren (aged about 7-8 years), fell from 18.3% to 0.2% (p<0.0001) and from 10.0% to 0.4% (p<0.0001) in Giza, respectively, and from 1.7% to 0% and 1.7% to 0% (both p=0.13) in Qalubyia, respectively. Mosquito infection rates fell from 3.07% (95% CI 2.38-3.88) to 0.19% (0.08-0.38) in Giza and from 4.37% (3.07-5.99) to 0% (0-0.05) in Qalubyia. INTERPRETATION: MDA greatly affects variables related to infection (microfilaraemia and circulating filarial antigenaemia prevalence rates) and transmission (antifilarial antibodies in young children and mosquito infection rates). Our results suggest that after five rounds of MDA filariasis is likely to have been eliminated in most endemic localities in Egypt.

Assessment of Leptoconops bequaerti as a potential vector of Mansonella ozzardi in Haiti.

Experimental studies in Bayeux, Haiti showed that the biting midge, Leptoconops bequaerti, is capable of supporting the complete development of Mansonella ozzardi but only on a very limited scale. This suggests that the species may not be involved in the natural transmission cycle despite its abundance and pestiferous nature in certain areas of Haiti. A midge-holding container is described which markedly enhanced the survival of engorged L. bequaerti in the laboratory.