Abstract:
Bancroftian filariasis is one of the major vector-borne diseases in Sri Lanka.
Therefore, this study was mainly focused on finding out the dynamics of the
indoor-resting filarial vector, Culex quinquefasciatus, to understand the present
status of filariasis in Polhena, Matara. Under the vector dynamics the density of the
vector, the effect of housing conditions on their density and their infection and
infectivity rates were studied. The entomological collections of morning indoor-resting mosquitoes were carried out biweekly from late November 2002 to late
March 2003 in the study site. Eight mosquito species were recorded in the
collections and C. quinquefasciatus females showed the highest abundance (80%).
The population density of the vector varied throughout the study period between a
minimum of 8.00 and a maximum of 44.80 C. quinquefasciatus per man-hour
(mean = 17.52). This variation showed a significant relationship (P < 0.05) with the
rainfall received to the area. The density of the vector within the study period
showed a significant increase (P < 0.05) when compared with the year 1992. Also
there is a statistically significant relationship between housing conditions and the
vector abundance (P < 0.05). Among collected mosquitoes, C quinquefasciatus
females were dissected to investigate the presence o f life cycle stages of
Wuchereria bancrofti, the parasite of bancroftian filariasis. These data were used to
calculate the infection and infectivity rates of the vector in Polhena. Infection of C.
quinquefasciatus with W. bancrofti continued throughout the study period and the
infection rate varied between 2% - 15%. Infective mosquitoes were found
occasionally. Therefore, the infectivity rate is a discontinued one (recorded only in
late November - 0.89% and late February - 3.80%). A highly significant reduction
in the infection rate (P <0.01) and a significant reduction in the infectivity rate (P
< 0.05) has resulted in Polhena when compared with the rates (infection and
infectivity) in year 1992. This may be due to the Mass Drug Administrations
(MDAs) that operated in the area from year 1999.
