DDT & deltamethrin resistance status of known Japanese encephalitis vectors in Assam, India.

Background & objective: Japanese encephalitis (JE) outbreaks are common in Assam, northeastern State of India. Information on resistance in known JE vectors in the affected area is important for effective control measures. This study was undertaken to determine the species abundance of JE vectors endemic to Sibsagar district of Assam, and their susceptibility against DDT and deltamethrin. Methods: Adult mosquitoes were collected using CDC light trap and aspirators from human dwellings from 13 endemic villages falling under three Primary Health Centres. Collected mosquitoes were identified and unfed female mosquitoes were used for DDT and deltamethrin sensitivity bioassay. The bioassay was performed following WHO protocol using standard susceptibility test kit. Knockdown time (KDT) was monitored at every 10 minutes intervals, whereas mortalities were recorded 24 h post-exposure. Vector density and resistance status were mapped using geographic information system (GIS) technique. Results: A total of 7655 mosquitoes were sampled under three genera, i.e. Anopheles, Culex and Mansonia, and nine species, the JE vector Cx. vishnui group (31.78%) was the most predominant species, followed by Ma. uniformis (16.81%) and Ma. indiana (16.45%). All vector species were suspected to be resistant to DDT and sensitive to deltamethrin, except Ma. indiana, which was suspected to deltamethrin resistant. The KDT50 and KDT95 values of vector mosquitoes for DDT were significantly higher as compared to deltamethrin. The probit model used to estimate KDT50 and KDT95 values did not display normal distribution of percentage knockdown with time for all the vectors tested for DDT and deltamethrin, except for Ma. indiana for deltamethrin assay and Cx. gelidus for the DDT assay. Interpretation & conclusion: Differences in insecticide resistance status were observed between insecticides and vector species. The results of this study provided baseline data on insecticide resistance in known JE vectors of Sibsagar, Assam. The maps generated may allow better communication in control operations and comparison of changes in susceptibility status of these vectors over time.

Malaria situation in forest-fringed villages of Sonitpur district (Assam), India bordering Arunachal Pradesh during an outbreak.

BACKGROUND & OBJECTIVES: Epidemiological and entomological studies were undertaken in forest-fringed villages in Sonitpur district (Assam) bordering Arunachal Pradesh, India to assess the malaria situation. Blood smears (thick and thin) were collected from the fever cases through door-to-door survey. Both the blood smears stained with Giemsa were used for malaria parasite detection. Slide positivity rate (SPR) was recorded as 39.1% with predominance of Plasmodium falciparum (97.1%) infections. Children between 5 and 14 yr showed higher rates of infection. METHODS & RESULTS: Over all malaria prevalence was higher among the males (SPR 43.2%) than in females (SPR 34.5%). Adult mosquito collection was made using CDC miniature light-traps from dusk-to-dawn. Per-trap night density of mosquitoes in human dwellings and cattlesheds were 289 and 925, respectively. Anopheles minimus and An. dirus, the major vectors of malaria in Northeastern region of India formed 33.2% of the total vectors recorded. An. dirus could be recorded only from human dwellings. The results showed high malaria risk in the study villages. INTERPRETATION & CONCLUSION: High vector density with high parity rate, poor socio-economic conditions, lack of awareness, poor sanitation and congenial atmosphere for mosquito proliferation are aggravating the malaria situation in the study area.

The drug sensitivities of Plasmodium falciparum in the Sonitpur district, Assam, India.

Falciparum malaria is an ongoing problem in the foothills of Northeast India. Evaluation of the drug sensitivities of P. falciparum was carried out in four endemic villages of the Sonitpur District of Assam, involving 218 cases who were tested in vivo over 35 days. Chloroquine resistance was detected at the RI level in 29 cases (13%) and RII level in 8 cases (4%). No RIII chloroquine resistant cases were detected in the study. RI resistance was observed in the age groups 6-10 years, 11-14 years, and 15 years and above in 16%, 17%, and 13%, respectively. RII level resistance was observed in 4% of all those groups combined. All the RI and RII resistant cases responded well to a single dosage of Metakelfin (sulfamethoxypyrazine I.P 1,500 mg and pyrimethamine I.P 75 mg).

Epidemiological and entomological aspects of malaria in forest-fringed villages of Sonitpur district, Assam.

BACKGROUND & OBJECTIVES: Detailed epidemiological and entomological studies were undertaken in forest-fringed villages and a Tea Estate in Sonitpur, Assam to assess the malaria situation. METHODS: Door-to-door active surveillance was carried out to collect blood samples. Thick and thin blood smears stained with Giemsa were used for malaria parasite detection. Mosquito collections were made using CDC miniature light-traps and hand catch methods from dusk-to-dawn. RESULTS: 48% SPR, 49.1 Pf% was recorded from the study villages. Children between 10 and 14 years were most sufferers. Per trap night density of mosquitoes in human dwellings was 204.3 and in cattlesheds--908.7, An. minimus accounted for 20.7% of total malaria vectors. INTERPRETATION & CONCLUSION: The results showed high malaria risk in the study villages. High vector density with high parity rate, poor socio-economic conditions, lack of awareness, poor sanitation and congenial atmosphere for mosquito proliferation are aggravating the malaria situation more complex in the study area.

Evaluation of botanicals as repellents against mosquitoes.

Repellent properties of three plant extracts--essential oil (steam distillate) of Zanthoxylum limonella (fruits), Citrus aurantifolia (leaf) and petroleum ether extract of Z. limonella (fruits) were evaluated as repellent against Aedes (S.) albopictus mosquitoes in mustard (Dhara) and coconut (Parachute) oil base under laboratory conditions. Three concentrations--10, 20 and 30% of the repellents were evaluated. Repellents in mustard oil afforded longer protection time against the bites of Aedes (S.) albopictus mosquitoes than those in coconut oil. At 30% concentration, 296-304 min protection time was achieved by the test repellents in mustard oil base while repellents in coconut oil exhibited 223.5-245 min protection time at the same concentration. Oil of Z. limonella gave the highest protection time against the bites of Aedes (S.) albopictus mosquitoes at all the concentrations than other herbal repellents tested both in mustard and coconut oil.

Field evaluation of herbal mosquito repellents.

Repellent properties of Zanthoxylum armatum DC. Syn. Z. alatum Roxb. (Timur), Curcuma aromatica (Jungli haldi) and Azadirachta indica (Neem) oils were evaluated against mosquitoes in mustard (Brassica sp.) and coconut (Cocos sp.) oil base and compared with synthetic repellent. Dimethyl phthalate (DMP) as standard. Timur and jungli haldi afforded better protection in the both the base at all the concentrations. Tepellents in mustard oil gave longer protection time than those in coconut oil. At 0.57 mg/cm2 concentration timur oil gave significantly higher protection both in mustard (445 min) as well as coconut oil (404 min) than the other repellents and DMP.

Role of Anopheles culicifacies during an outbreak of malaria in Gorubandha P.H.C., Assam.

Entomological investigation during an outbreak of malaria in Gorubandha PHC in Sonitpur district revealed unusually high density of Anopheles culicifacies followed by An.minimus. Parity rates of both the species were very high, 65% and 62.2% respectively. An. culicifacies was incriminated as malaria vector. Sporozoite rate recorded was 0.63%. Both the species were found susceptible to DDT. This substantiates the epidemiological observation which yielded 98% Plasmodium falciparum malaria out of 35.2% malaria positive cases. Incrimination of An. culicifacies means adding one more malaria vector to this region.