Bancroftian filariasis: patterns of vector abundance and transmission in two East African communities with different levels of endemicity

Abstract

Intensive monitoring of Wuchereria bancrofti vector abundance and transmission intensity was carried out in two communities, one with high-level endemicity for bancroftian filariasis (Masaika, Tanzania) and the other with low-level (Kingwede, Kenya), on the East African coast. Mosquitoes were collected in light traps, from 50 randomly selected households in each community, once weekly for 1 year. They were identified, dissected and checked for parity and filarial larvae. Anopheles gambiae s. l., An. funestus and Culex quinquefasciatus transmitted W. bancrofti in the two communities but the importance of each of these taxa differed between the communities and by season. The overall vector densities and transmission intensities were significantly higher in Masaika than in Kingwede (the annual biting rate by 3.7 times and the annual transmission potential by 14.6 times), primarily because of differences in the available breeding sites for the vectors and in the vectorial capacity of the predominant vector species. A marked seasonal variation in vector abundance and transmission potential contributed to the complex transmission pattern in the communities. Generally, these indices were higher during and shortly after the rainy seasons than at other times of the year. Considerable differences in W. bancrofti transmission were thus observed between communities within a relatively small geographical area (mainly because of environmentally-determined differences in vector habitats), and these were reflected in the marked differences in infection level in the human populations. The variation in vector abundance, vector composition and transmission intensity in the two communities is discussed in respect to its cause, its effects, and its significance to those attempting to control bancroftian filariasis.

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

“…A longitudinal entomological survey was carried out in 50 randomly selected houses for 1 year, from July 1998 to June 1999, as described by Rwegoshora et al (2005). Briefly, in each selected house, a batteryoperated CDC light trap was placed, on one night each week, beside an occupied bed provided with an un-impregnated mosquito net.…”

“…The results of several studies on bancroftian filariasis in coastal East Africa have shown that the human infection and disease burden vary considerably from one community to the other within the same endemic area (White, 1971;Wijers, 1977;McMahon et al, 1981;Meyrowitsch et al, 1995;Simonsen et al, 1995;Wamae et al, 1998;Mukoko et al, 2004). In a study recently carried out in a community of high endemicity and another of low endemicity, both in coastal East Africa, it was found that the much higher intensity of transmission and rates of human infection and disease seen in the highly endemic community were clearly associated with considerably higher vector densities (Simonsen et al, 2002;Rwegoshora et al, 2005), and that the differences in level of endemicity appeared to result primarily from differences in the mosquito breeding habitats in the two communities.…”

“…When it comes to the microepidemiological household level, additional factors, such as the characteristics of the houses and their inhabitants, may affect transmission and infection. The aims of the present study were to investigate the differences in vector density between different households within Masaika, the high-endemicity community studied by Rwegoshora et al (2005), and then determine to what extent these differences were reflected in differences in transmission and human infection.…”

Immunoepidemiology ofWuchereria bancroftiInfection: Parasite Transmission Intensity, Filaria-Specific Antibodies, and Host Immunity in Two East African Communities

“…Briefly, in Masaika and Kingwede there were 950 and 1,013 inhabitants who were 1 year old or older; the overall mf prevalence and the overall CFA prevalence in these individuals were 25.5 and 52.2%, respectively, in Masaika and 2.9% and 16.4%, respectively, in Kingwede. Thus, the prevalence of lymphatic filariasis was higher in Masaika than in Kingwede, a fact that was reflected in a much higher level of transmission in Masaika than in Kingwede (the annual transmission potentials were 92.9 and 6.4, respectively, during the year preceding the surveys reported here [39]). The study was approved by the Medical Research Coordinating Committee of the National Institute for Medical Research, Tanzania, the Kenyatta National Hospital Ethical and Research Committee, Kenya, and the Central Scientific-Ethical Committee, Denmark.…”

“…We present here results from one such comparative immunoepidemiological analysis in which we focused on comparing observed age relationships between filarial specific antibody responses and W. bancrofti intensity in a community with low parasite transmission intensity in coastal East Africa with the relationships observed in a community in the same region with a higher transmission intensity (25,39,43). One feature of the analyses reported here was the use of a combined empirical data analysis and mathematical modeling approach for investigating mechanisms that may underlie the observed differences in the age patterns of parasite-specific antibody responses between communities exposed to different transmission pressures (24,25,50,51).…”