Bancroftian filariasis: house-to-house variation in the vectors and transmission — and the relationship to human infection — in an endemic community of coastal Tanzania

Abstract

The house-to-house variation in Wuchereria bancrofti vector abundance and transmission intensity, and the relationship of these parameters to human infection, were investigated in an endemic community in coastal Tanzania. Vector mosquitoes were collected in light traps set up in 50 randomly selected households once weekly for 1 year. They were identified, dissected and checked for filarial larvae. Vector densities and transmission potentials varied markedly between households, both for all vectors combined and for the individual vector species (Anopheles gambiae s.1., An. funestus and Culex quinquefasciatus), even between households located close to each other. The variation in vector abundance was probably mainly attributable to differences in the distance to breeding sites, to specific household features likely to ease mosquito entry and hiding, and to the number of household inhabitants. Household annual biting rates (ABR) correlated positively with household annual transmission potentials (ATP), indicating that intense vector biting led to a high transmission intensity. Intriguingly, however, the human filarial-infection status (as indicated by microfilaraemia or circulating filarial antigenemia) did not differ significantly between households with relatively high and lower ABR or ATP. Possible reasons for this result include the long time required for W. bancrofti infection to establish in humans, human behaviour affecting exposure, the sharing of mosquito populations between households, and differential susceptibility of humans to infection. The marked heterogeneity in exposure between households, and the lack of immediate relationship between transmission and detectable human infection at household level, should be taken into account when considering the transmission pattern of lymphatic filariasis.

Association between Mannose-Binding Lectin Polymorphisms and Wuchereria bancrofti Infection in Two Communities in North-Eastern Tanzania

“…The frequently noted family and household clustering in lymphatic filariasis has generally been ascribed to variation in individuals' exposure to infection, 10 adaptive immune responsiveness, 31 or genetic composition. 16 There is accumulating evidence that host genetics is an important determinant of infection and morbidity in several helminth infections, including schistosomiasis and ascariasis.…”

“…This notion is supported by the very static infection patterns observed in long-term follow-up studies. [6][7][8][9] Clustering of infection could be an effect of individual differences in exposure to infective vectors, which has been shown to vary considerably within the endemic community, 10 or in adaptive immune responsiveness, which e.g. may be affected by the infection status of the mother during pregnancy.…”

Comparison of Methods for Xenomonitoring in Vectors of Lymphatic Filariasis in Northeastern Tanzania

“…18,19 A detailed description of the village is provided by Rwegoshora and others. 7 In this village, 12 households were recruited for mosquito trapping that was conducted from September 6 to October 14, 2011. Vyeru is a village on Manza Bay (S 04.95754, E 39.13483).…”

“…4 Second, mosquitoes can be collected and tested (xenomonitoring), either through dissection to find the filarial larvae, or through the use of molecular methods to detect the DNA of the filarial worms. 5 Light traps are commonly used for the collection of mosquitoes for LF xenomonitoring, [6][7][8] and are usually placed indoors near a sleeping person who is protected with an untreated mosquito net. Other methods such as human landing catches have been used, 9 but this method is used less often due to ethical concerns.…”

A simple and efficient tool for trapping gravid Anopheles at breeding sites

“…Oviposition traps have also been developed for Culex [5] and Aedes mosquitoes [6-10]. However, to our knowledge, there is no efficient oviposition trap for gravid Anopheles , which include malaria and lymphatic filariasis vectors [11]. Such a tool would help in understanding the physiology of gravid females in the wild, distances travelled for oviposition, the characteristics of productive breeding sites and whether gravid mosquitoes deliberately choose these, and for general mosquito surveillance.…”