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

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.

Implication of diethylcarbamazine induced morbidity and the role of cellular responses associated with bancroftian filariasis pathologies.

Pre and post-diethylcarbamazine treatment clinical expression, microfilaraemia prevalence and cellular responses were investigated in individuals in Tanga, Tanzania. Fifty-seven male individuals (aged = 15 years old) were identified for further studies on IL-4, IL-6, IL-8. IFN-gamma, IL-beta, TNF-alpha and nitric oxide in plasma and hydrocoele fluid. Microfilarial prevalence in the examined individuals was 12% with a geometric mean intensity (GMI) of 838 mff/ml in a community with a population of 1018 individuals. Microfilaraemic hydrocoele stage II and III were the most frequent pathologies observed with prevalence of 17.5% and 42. 1 %, respectively. All study individuals treated with diethylcarbamazine (DEC) standard dose of 6 mg/kg experienced post-treatment adverse events. There was no direct relationship between elevated IL-6 and the occurrence and severity of clinical adverse effects post-treatment. The findings from this study suggests that, blood elevated cytokine profile is not the main etiological factor in the inflammatory responses developing after treatment of bancroftian filariasis infections and pathology with DEC. Plasma levels of cellular (cytokines) responses during treatment revealed a proportion of symptomatic patients. Prior to treatment, patients with hydroecoele had high levels of IL-6 than those without the pathology. In conclusion these findings do not support the hypothesis that pro-inflammatory cytokines are directly responsible for adverse events to DEC chemotherapy in bancroftian filariasis infections and pathologies such as hydrocoele, lymphoedema and elephantiasis.

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

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.