Impact of single dose of diethylcarbamazine and other antifilarial drug combinations on bancroftian filarial infection variables: assessment after 2 years.

The impact of single dose mass drug administration of diethylcarbamazine (DEC), DEC with albendazole (ALB), and ivermectin (IVR) with albendazole, was examined on the human bancroftian filarial infections in village scale trials in south India, from a follow-up study after 2 years. The treatment arms administered with DEC alone and DEC+ALB demonstrated long-term benefits in reducing microfilaraemia significantly (P<0.05), while antigenaemia reduction was negligible. The arm with ALB+IVR did not show such reductions. Among the antigenaemic and microfilaraemic individuals, 87% became amicrofilaraemic in DEC+ALB arm, which were higher than that observed in the other 2 treatment arms. Among amicrofilaraemics (but Ag+), nearly 35% cleared of infection in DEC+ALB, while 26% and 6% in DEC alone and IVR+ALB arms, respectively. The drug combination DEC+ALB was observed to demonstrate a significant impact in reducing filarial infection even after 2 years post treatment.

Mosquito blood feeding patterns as a factor in the epidemiology of Japanese encephalitis in southern India.

Determinations were made of the source of 16,330 bloodmeals from 10 species of Culex mosquitoes, including recognized vectors of Japanese encephalitis (JE) virus, in two epidemiologically distinct areas in southern India. In Madurai, where cases occurred sporadically and pigs were reared only in some villages, Cx. tritaeniorhynchus, Cx. pseudovishnui, and Cx. vishnui had fed predominantly on cattle (89.2-91%), but less frequently on humans (2.1-6.2%) and on pigs and ardeid birds (0-0.1%). In Nallur, which was endemic for JE and had a large pig population, 4.4-5.4% of the feedings were on these hosts. Cattle feedings accounted for 84.6-88% of the total feedings, human feedings for 2.4-6.2%, but there were no ardeid-positive feedings. Culex tritaeniorhynchus and Cx. vishnui showed a marked increase in the proportion of human feedings during the hot season, due to increased availability of humans sleeping outdoors to mainly exophagic mosquitoes. Feeding indices were corrected for spatial and temporal concurrence of hosts in each season, but these factors were found to require further elucidation. Discrepancies in the relative abundance of vectors as monitored by two different methods are discussed in the light of these observations.

Surveillance for Japanese encephalitis in villages near Madurai, Tamil Nadu, India.

A simple dusk index was developed to monitor the density of recognized vectors of Japanese encephalitis virus (JEV) based on hand catches around cattlesheds at dusk and parous rates. When used routinely in combination with sentinel animal studies for surveillance in villages with a high prevalence (46.2%) of neutralizing antibodies against JEV in children under 16 years, there was a peak in vector density and virus activity during the north-east monsoon period, October-December. The reasons for an unusual outbreak of cases of encephalitis during the summer months of 1984 are discussed.

Sustainability of soil-transmitted helminth control following a single-dose co-administration of albendazole and diethylcarbamazine.

We evaluated the long-term impact of single-dose diethylcarbamazine plus albendazole combination therapy with that of diethylcarbamazine alone on the control of soil-transmitted helminths (STH) in 2 blocks (revenue units) of Villupuram district, south India, as part of an ongoing mass drug administration (MDA) campaign for the elimination of lymphatic filariasis in 2001. The prevalence and intensities of STHs were studied in 287 children, aged 9 and 10 years (136 in the combination therapy cohort and 151 in the diethylcarbamazine alone cohort), using the Kato-Katz technique to examine stool samples at 4 time-points (baseline, and 3 weeks, 6 months and 11 months after MDA). The combination therapy showed long-term efficacy against STHs and the magnitude of control remained at a moderate and significant level for 11 months after MDA compared with the moderate gains of diethylcarbamazine alone. Single-dose MDA with albendazole and diethylcarbamazine combination therapy may prove to be a good strategy in treating multiple parasitic infections in endemic communities.

Impact of two annual single-dose mass drug administrations with diethylcarbamazine alone or in combination with albendazole on Wuchereria bancrofti microfilaraemia and antigenaemia in south India.

A two-arm community-based lymphatic filariasis elimination trial is being carried out in Tamil Nadu state, India to assess the effect of 2 annual single-dose mass drug administrations of diethylcarbamazine + albendazole (DEC + ALB) on microfilaraemia and antigenaemia in one arm, and diethylcarbamazine(DEC) alone in the other arm. In a cross-sectional survey at each time-point, 450-650 subjects in childhood (2-9 years old) and young adulthood (10-25 years old) were screened from each treatment arm. After 2 annual mass drug administrations, microfilaraemia prevalence in the 2-drug arm was reduced by 54% and 62% in the 2-9 year old and 10-25 year old groups respectively; and corresponding figures for the single-drug arm were 26% and 37%. Though higher reductions were recorded for geometric mean intensity of microfilaraemia in the 2-9 year old groups for both treatment arms, reduction was more pronounced in the 2-drug arm than the single drug arm (74% vs. 24%) in the 10-25 year old group. The reduction in the antigenaemia prevalence in the 2-9 year old group was evident in both treatment arms, but in the 10-25 year old group the reduction was only 16.8% in the 2-drug arm. Our results suggest that the annual, single-dose combination (DEC + ALB) mass treatment regimen has an enhanced effect against bancroftian filariasis compared to single-drug therapy.

Space-spraying with malathion as a supplementary measure for operational malaria control.

Entomological studies showed that due to outdoor resting by the vector Anopheles culicifacies as well as poor spray coverage, indoor residual spraying with malathion was ineffective in malarious villages of the Thenpennai riverine tract in Tamil Nadu. Over a 4 yr period during which residual spraying was supplemented with ground applications of malathion space spraying, the slide positivity among patients with fever fell from 21.04 to 1.1 per cent. In mass blood surveys 0.7 per cent persons surveyed at the beginning of the study were positive for the malarial parasite, but no positives were detected in the last survey, in 1984. There was a rising trend in malaria incidence in riverine villages outside the programme.

Field efficacy of "Mosbar" mosquito repellent soap against vectors of bancroftian filariasis and Japanese encephalitis in southern India.

Deet-permethrin "Mosbar" soap was field tested for repellency against mosquitoes by volunteers in urban and rural localities in southern India. Eighty-nine to 100% reduction in man-vector contact was recorded for 8 mosquito species, including Culex quinquefasciatus and recognized vectors of Japanese encephalitis. The soap was highly acceptable to the community.

Development of a high level of resistance to Bacillus sphaericus in a field population of Culex quinquefasciatus from Kochi, India.

Field resistance to Bacillus sphaericus was observed in a population of Culex quinquefasciatus in Kochi, India, exposed to 35 rounds of spraying with a formulation of B. sphaericus 1593 M over a 2-year period. Larvae from the sprayed area gave LC50 and LC90 values that were 146 and 180 times greater than corresponding values for a susceptible strain from an unsprayed locality. When the resistant strain was colonized in the laboratory and subjected to moderate selection pressure at each generation, resistance rapidly increased and by the 18th generation it was 6,223 and 31,325 times greater at the LC50 and LC90 levels in comparison with the susceptible strain. There were no significant differences among 6 susceptible strains tested. Tests were repeated and validated using the standard primary powder SPH88, B. sphaericus 2362. No cross resistance was observed against B. thuringiensis H-14.

Cross-resistance to Bacillus sphaericus strains in Culex quinquefasciatus resistant to B. sphaericus 1593M.

Bacillus sphaericus 1593M resistant larvae of Culex quinquefasciatus were reared in the laboratory since 1995. Resistance in the larvae was monitored by subjecting selection pressure using B. sphaericus 1593M at every generation. Bioassays were conducted with different strains of B. sphaericus (Bs 2297, Bs 2362 and Bs IAB 59) and confirmed cross-resistance in the present study. The level ranged between 27.3 to 18.2 fold in comparison with susceptible larvae. But Bacillus thuringiensis var israelensis strains (Bti PG14 and Bti 426) did not show any cross-resistance in the larvae and it emphasized a need to study the mode of action of B. sphaericus toxin that induces cross-resistance in the larval strain.