Laboratory wash-resistance and field evaluation of deltamethrin incorporated long-lasting polyethylene netting (Netprotect(®)) against malaria transmission in Assam, north-east India.

North-east India is co-endemic for Plasmodium falciparum and P. vivax malaria, and disease transmission is perennial and persistent. This study reports the results of a field-based village scale trial of deltamethrin incorporated long-lasting polyethylene netting (Netprotect(®)) conducted in P. falciparum predominant pocket of Assam, north-east India to assess operational feasibility, acceptability and sustainability against disease vectors and malaria transmission. The study monitored the residual efficacy of the long-lasting net in relation to serial washings in the laboratory and malaria prevalence in experimental villages for the first year of investigations from September 2008 to June 2009. The mosquito vector populations of Anopheles minimus were observed to be highly susceptible to deltamethrin (0.05%), and follow up investigations revealed that the vector mosquito had virtually disappeared in Netprotect(®) intervention villages. Concurrently, there was consistent decline in malaria cases in Netprotect(®) villages and transmission reduction was statistically significant compared to untreated net (net without insecticide) and no-net control villages for the corresponding study period. The contact cone-bioassay investigations against malaria transmitting mosquito species revealed that the bioavailability of the insecticide on the net fiber was persistent up to 20th serial wash resulting in ≥80% mortality. Community compliance and acceptance were high, and users reported decreased nuisance due to biting mosquitoes. It was concluded that deltamethrin incorporated polyethylene long-lasting netting was safe, wash-resistant, and assessed to be an operationally feasible, community-based intervention for sustainable management of disease vectors to prevent malaria transmission.

Wash-resistance and field efficacy of Olyset net, a permethrin-incorporated long-lasting insecticidal netting, against Anopheles minimus-transmitted malaria in Assam, Northeastern India.

INTRODUCTION: The long-lasting insecticidal nets are ready-to-use, pretreated nets, which do not require retreatment for 4-5 years. Olyset nets that are made of high-density polyethylene monofilament yarn with 2% w/w permethrin incorporated (corresponding to 1 g/m(2)) are type-2 in which insecticide is incorporated into the polymers and are wash resistant. In these, insecticide migrates to the surface of the netting fiber to be bioavailable against mosquitoes and other insect pests. STUDY SITE AND OBJECTIVES: The present study was a village scale, field-based trial that was conducted in Plasmodium falciparum predominant area of Assam to assess feasibility, acceptability, and sustainability of this intervention against vector populations and disease transmission. We here report the research findings of Olyset net as an intervention against Anopheles minimus-transmitted malaria in foothill area of Assam for the first year of observations beginning July 2005 till June 2006. RESULTS: An. minimus, the mosquito vector species, was observed to be fully susceptible to permethrin. Follow-up investigations revealed that An. minimus mosquitoes had virtually disappeared in Olyset net villages, which was corroborated by data on human bait mosquito-landing catches. There was a consistent decline in the malarial incidence in Olyset net intervention villages, and the overall impact on the malarial transmission was significant compared to untreated net and no-net control villages for the corresponding study period. The bioavailability of insecticide on Olyset netting fiber was consistent (100% kill effect) up to 10 months of monitoring, and was observed to be wash resistant even after the 20th wash at fortnightly intervals. CONCLUSIONS: The Olyset nets were safe to use, wash resistant, and assessed to be operationally feasible, community-based intervention for sustainable management of disease vectors against malaria. Community compliance and acceptance was high, and users reported decreased nuisance due to biting mosquitoes.

Wash resistance and residual efficacy of long-lasting polyester netting coated with alpha-cypermethrin (Interceptor) against malaria-transmitting mosquitoes in Assam, northeast India.

Malaria is endemic in Assam, northeast India, with low-to-moderate transmission of the causative parasites, mostly by Anopheles minimus. Plasmodium falciparum is the predominant parasite (>60%), with remaining cases being due to P. vivax. As an alternative intervention for malaria control, long-lasting insecticidal nets [Interceptor coated with alpha-cypermethrin 10% suspension concentrate (SC), 0.667% w/w, 0.2g/m(2)] underwent field evaluation for laboratory wash resistance and residual efficacy in field conditions against malaria-transmitting mosquitoes. Based on entomological observations, the Interceptor net intervention was the most effective, corresponding to the lowest mosquito vector density in experimental villages. There was virtual disappearance of A. minimus in Interceptor net villages in contrast to the untreated net intervention and the no-net control. Contact cone bioassay tests revealed 100% mortality in the A.minimus group of mosquito species in the community using the Interceptor net, which was consistent during the follow-up monitoring period (October 2006 to April 2007) in field conditions. Similar levels of mortality were observed in laboratory-washed nets compared with unwashed nets, and wash resistance was consistent even after the 20th serial wash at fortnightly intervals. Community compliance and acceptance of the Interceptor net was high, with decreased nuisance due to biting mosquitoes and other household insect pests being reported.

Malaria parasite burden and treatment seeking behavior in ethnic communities of Assam, Northeastern India.

OBJECTIVES: The objectives of the study were to define the infectious reservoir of malaria with particular reference to transmission dynamics of Plasmodium falciparum, and to ascertain the disease trends in view of the existing containment practices and treatment seeking behavior in malaria endemic communities of Assam, India. METHODS: Cross-sectional surveys were conducted in population groups of malaria endemic districts of the state to determine parasite prevalence, and data were analysed retrospectively for the years 1991-2003 to ascertain the disease trends. Structured questionnaire based surveys were conducted to study the treatment seeking behavior and practices of healthcare providers. RESULTS: P. falciparum and P. vivax were the only two parasite species encountered, the former being in the majority (>60%). Malaria transmission was persistent, and a seasonal peak of P. falciparum was consistently observed during the months of heavy rainfall (April to September). Among children (5-15 years) there was a significantly higher malaria parasite rate as compared to the <5 years age group and adults (>15 years). There was a decline in parasite rates for all age groups over the years of the study that could not be attributed to vector control intervention intensities and/or meteorological factors. CONCLUSIONS: The persistence of P. falciparum is attributed to the emergence of drug resistant varieties, inadequate interventions and treatment seeking patterns, and for its containment focused intervention measures are advocated in partnership with the communities.

Multi-drug resistant Plasmodium falciparum malaria in Assam, India: timing of recurrence and anti-malarial drug concentrations in whole blood.

The susceptibility of 23 cases of Plasmodium falciparum malaria from the Sonapur primary health center in the Kamrup district of Assam, India to different antimalarials was investigated using the 28-day World Health Organization in vivo test. Whole blood concentrations of chloroquine, sulfadoxine, and quinine were determined at different intervals and at the time of parasites recrudescence after completion of treatment with the respective drugs to confirm the status of drug sensitivity. A case of multi-drug resistant P. falciparum malaria was found where recrudescence occurred, despite standard oral treatment with chloroquine, sulfadoxine/pyrimethamine, and quinine sequentially. Whole blood concentrations of chloroquine, sulfadoxine, and quinine at the time of recrudescence were 0.35 microg/ml (day 7), 18 microg/ml (day 14), and 0.009 microg/ml (day 14), respectively. Therefore, monitoring of drug-resistant P. falciparum malaria and its proper treatment should be intensified to check the spread of multi-drug resistant strains in other parts of the country.

Therapeutic efficacies of antimalarial drugs in the treatment of uncomplicated, Plasmodium falciparum malaria in Assam, north-eastern India.

In the Indian state of Assam, the current therapeutic efficacies of the drugs commonly used in the area for the treatment of uncomplicated, Plasmodium falciparum malaria were investigated. As is routine in this area, subjects found positive for P. falciparum malaria were initially treated with chloroquine (CQ). They were given sulfadoxine-pyrimethamine (SP) if this treatment failed, and subsequently quinine if the SP failed. The protocol of the World Health Organization's extended in-vivo test was used to follow parasite clearance and clinical cure. Therapeutic response was assessed by comparing the baseline (day-0) level of parasitaemia with that observed on day 3. Many (75.7%) of the 144 evaluable subjects were treatment successes after CQ, but six early (4.2%) and 29 (20.1%) late CQ-treatment failures were observed. Of the 34 CQ-treatment failures followed, 31 (91.2%) responded adequately to SP but the other three were early (one) or late (two) SP-treatment failures. Two (66.7%) of the SP-treatment failures responded adequately to parenteral quinine but the other (a late quinine-treatment failure) had to be given an artemisinin derivative to achieve a clinical cure. The foci in which multidrug-resistant cases of malaria are developing in India need to be identified quickly, so that such cases can be cured before the mutant strains of P. falciparum that are resistant to several drugs have a chance to become more widespread.

Morbidity and mortality due to malaria in Tarajulie Tea Estate, Assam, India.

Beginning 1991, a sudden rise of malaria cases were recorded in Tarajulie TE (Assam) coupled with mortality due to malaria. Deaths were confirmed due to Plasmodium falciparum (Pf) infections and were recorded in all age groups excluding infants. Malaria positives were recorded in all months of the year, however, there was a increased hospital attendance due to fever/malaria positives during May to September. During the years (1991-1993), the slide positive rate was as high as 33.04%, mostly being Pf infections (69%), and the annual parasite index ranged between 6 to 304 per thousand population. Morbidity and mortality due to malaria were attributed to labor movements to and fro from garden premises to adjoining hamlets, the latter being the site of acquisition of the infections.

Susceptibility of Plasmodium falciparum to chloroquine in tea garden tribes of Assam, India.

P. falciparum was the predominant parasite ( > 80%) species in malaria ridden tea estates of Assam. A simplified 3 day in vivo test to determine chloroquine sensitivity in tea garden tribes revealed that the majority of the cases (85%) were S/RI, 7% were RI, and 3% were RII and 5% were RIII, respectively. Early case detection and treatment were deemed necessary to reduce morbidity and mortality due to P. falciparum in these tea estates.