House-scale evaluation of bifenthrin indoor residual spraying for malaria vector control in India.

In an area of India where the main rural malaria vector, Anopheles culicifacies Giles, has developed triple resistance to DDT, HCH, and malathion sprayed indoors in antimalaria program, bifenthrin (10% wettable powder) was evaluated in a randomized house-scale trial between July 1999 and March 2000. Entomological impact of four serial doses of bifenthrin (25, 50, 100, and 200 mg/m2) sprayed in rooms in five villages was compared with malathion (2 g/m2) and unsprayed control. An. culicifacies was 100% susceptible to bifenthrin (0.1%), but only 57% to malathion (5%) test papers. Contact bioassays were carried out on sprayed surfaces for 24 wk, and 24 h mortality in An. culicifacies was recorded. Bifenthrin 100- and 200-mg doses caused > or = 80% mortality until 24 wk. The 50-mg dose caused > or = 80% mortality on tin, wood, and mud surfaces for 24 wk, and on brick walls for 16 wk. Bifenthrin 25-mg dose produced > or = 80% mortality for 24 wk on tin, 20 wk on mud walls, 16 wk on brick walls, and 8 wk on wood surfaces. Persistence of > or = 80% mortality did not differ for 25- and 50-mg doses on any surface except on wood (P < 0.05). Malathion sprayed in three rounds of 6 wk apart caused > or = 80% mortality for 16 wk on the brick and mud walls, and for 20 wk on the tin and wood surfaces. Bifenthrin 25- and 50-mg doses produced a similar impact on the densities of An. culicifacies and other mosquitoes but a superior one to malathion or control. Bifenthrin 25-mg dose caused least excitorepellency. Overall, efficacy of bifenthrin was superior to malathion. Considering the duration of the persistence of significant insecticidal action of bifenthrin on the most common surfaces (mud and brick walls), least excito-repellency and a relative impact on the mosquito densities, the 25-mg dose was the most superior among all the four doses evaluated.

Japanese Encephalitis epidemic in Anantapur district, Andhra Pradesh (October-November, 1999).

Epidemic of Japanese Encephalitis has occurred in Andhra Pradesh during October-November, 1999 affecting 15 out of 23 districts. In total, 873 cases with 178 deaths have been recorded up to the day 29.11.99. The epidemiological investigation has been done in Anantapur district in western Andhra Pradesh, where the outbreak has started in the third week of October. In the district 47 PHC have been affected. On an average 4.5 per cent of 3175 villages have been affected. Average number of cases per affected village have been 1.5. Rural population has been primarily affected. Age groups 1-14 years including infants have been affected but nearly 86.8% of cases have been among 1-9 year age group. The overall case fatality rate has been 18.4 per cent. Clinical features have been high fever, headache, altered sensorium, convulsions and coma. A marked seasonal onset of a few cases per village and 93.75 per cent of human serum samples collected from hospitalised cases showed the evidence of J.E. virus infection indicating that the present outbreak was due to JE virus. High density of Culex vishnui complex mosquitoes has been observed in the area. All the environmental and ecological conditions, temperature, rainfall and relative humidity have been in favour of JE transmission. Analysis of the data for the last 10 years showed that the human JE cases occurred in Anantapur in September-October months, which shifted to October-November, 99. Prolonged draught conditions were observed till October. Possibly the delayed monsoon and congenial atmospheric conditions after monsoon were favourable to the vector species for extra-human cycle of transmission in 1999. Low level transmission leading to small number of cases continued during the succeeding years every September-October till the present epidemic. In all 24 PHCs and urban towns were identified with 212 cases and 39 deaths till 29.11.99.

Some aspects of changing behaviour of malaria vectors in tribal areas of India.

The field entomological studies and surveys carried out in 72 tribal districts out of 100 in seven penninsular States namely, Andhra Pradesh, Bihar, Gujarat, Madhya Pradesh, Maharashtra, Orissa and Rajasthan indicated that in most of the areas the vector mosquitoes encountered during the present study were almost the same as recorded by the earlier workers except that Anopheles fluviatilis James, 1902 was recorded in the areas of district Raipur, Durg, Bilaspur, Raigarh, Shahdol, Rajnandgaon, Barwani and Janjgir of Madhya Pradesh, and Sundergarh of Orissa during the present survey. This vector was not recorded in earlier studies by other workers. An. culicifacies Giles, 1901 was not found in present survey in East Godavari and Vishakhapatnam of Andhra Pradesh and Ganjam and Koraput of Orissa where this mosquito was found in collections earlier. Similarly, An. fluviatilis was not encountered during the present field study in Bhilwara of Rajasthan, Phulbani and Kalahandi of Orissa, Thane, Nanded and Nasik of Maharashtra and Bharuch of Gujarat state. During this study An. fluviatilis was noted to be mostly endophilic whereas earlier workers noted this mosquito to be exophilic in a large number of districts. The majority of the tribal districts seem to be under the influence of two malaria vectors, An. culicifacies and An. fluviatilis and these tribal districts are maintaining a high malaria endemicity with predominance of Plasmodium falciparum infection. In the present study, the transmission seasons were noted to be longer than recorded earlier in the districts of Andhra Pradesh, Gujarat, Rajasthan and Orissa. In the remaining states it is almost similar as recorded earlier.

Blood meal identification by using Microdot ELISA in vector mosquitoes.

The blood meals of five mosquito species which are vectors for malaria, J.E. and Filaria were determined by using Microdot ELISA technique, which is a rapid and sensitive method. A total of 4354 freshly fed mosquitoes comprising of Anopheles culicifacies, An stephensi, Culex quinquefasciatus, Cx. vishnui gp. and Cx. tritaeniorhynchus were tested. Results of the study reveal that highest proportion of An. culicifacies between 76-100% fed on bovine host followed by 0.3 to 24.2% on human. Cx. vishnui showed 1.9% feeding on human, 49-87.7% on bovine and 7.4-12.3% on the pigs. It has been observed that malaria vectors namely An. culicifacies and An. stephensi are still zoophilic in nature. Similarly, the vector of J.E. namely Culex vishnui gp. and Cx. tritaeniorhynchus also fed on cattle but some samples have indicated feeding of blood meal from pigs.

Susceptibility status of malaria vectors to insecticides in India.

The use of chemical insecticides for control of malaria vector populations continues to be the mainstay of malaria control strategy in India. Monitoring vector susceptibility to chemical insecticides is an important activity under the National Malaria Eradication Programme to ensure judicious and effective use of chemical Insecticides. 72 entomological zones were established under NMEP in 1977 for undertaking entomological studies in the malaria problematic areas. These zones have been generating insecticide susceptibility data in respect of the various malaria vectors. In this paper the insecticide susceptibility data, in respect of major vectors of malaria as on 1997, is presented.

Malaria transmission during post-spray period of pirimiphos-methyl in Arunachal Pradesh.

Observations made for a period of four years from 1985 to 1988 on post-spray impact of pirimiphos-methyl (25 per cent Wp) on malaria vectors in Tirap district of Arunachal Pradesh showed that a low density (0.0 to 0.02 PMH) of Anopheles dirus was maintained in the areas sprayed with the insecticide at the dosages of 1 and 2 g/m2 from 1981 to 1984. The post-spray data (1985 to 1988) showed a reduction of 62.5 to 62.8 per cent in SPR, 55.6 to 64.7 per cent in SRF and 72.3 to 75.5 per cent decline in API as compared to baseline data of 1980 in areas sprayed with pirimiphos methyl.

Blood Cholinesterase monitoring in spraymen involved in malathion spraying--a health protection measure.

The blood Cholinesterase (ChE) level of malathion in spraymen is continuously monitored through a "built-in warning system" existing under NMEP since the introduction of malathion spraying. The data available from the States of Maharashtra, Punjab and Gujarat revealed that, in spraymen of Punjab, the ChE level in 1988 and 1989 remained normal in about 99.8 per cent spray personnel, and in 1 out of 381 workers, the ChE level fell to 62.5 per cent during 1989. In Gujarat and Maharashtra, the normal level of ChE was maintained in nearly 88 and 98.4 per cent of spray personnel respectively during the spraying period. The ChE level fell to 62.5 per cent in 11.9 per cent of spray staff in Gujarat during 1987 and in 1.5 and 1.6 per cent persons during 1988 and 1989 respectively in Maharashtra. Only in three cases (0.07 per cent) out of 4,100 in Maharashtra showed depression in ChE to 50 per cent in 1988. In none of the above mentioned cases, there was any parasympathetic overstimulation or uneasiness, etc, even then they were withdrawn from spray and were given rest and where needed medical care.

Success of integrated methods of control of mosquitoes in India--a review.

The integrated methodology for the control of vectors of diseases as well as mosquitoes has become an accepted concept amongst the public health experts. The feasibility of adopting this approach in different situations for mosquito control as per field trials by various institutions has been reviewed in this article. This concept, to some extent, has been in vogue under National Malaria Eradication Programme since long in a practicable way. Satisfactory results have been obtained wherever this approach has been applied carefully. The applicability of the integrated control methodology is not difficult provided various methods to be integrated are chosen and utilized in a rational way. Thorough health education is a prerequisite to awaken the community to accept the methods as part and parcel of routine life.

Field trial of the effectiveness of indoor-spraying with pirimiphos-methyl emulsion for malaria control in a tribal area of Phulbani district, Orissa State, India.

A field trial of malaria vector control was conducted in Phulbani district, Orissa, during 1984 and 1985. Indoor-spraying of pirimiphos-methyl emulsion formulation was undertaken at an application rate of 2 g/m2 in two sections (population 14,692) of Nuagaon Primary Health Centre. Houses in two adjacent sections (population 21,450) were sprayed with DDT a water dispersible powder (wdp) formulation at 1 g/m2 for comparison purposes. Operational problems in this area come from the tendency of tribal people to re-plaster over wdp applications. Pre-spray malariological indices in the trial area were 38% slide positivity rate, 37% slide falciparum rate and 12.1% annual parasite incidence. Densities of Anopheles annularis Van der Wulp, An. culicifacies Giles, An. fluviatilis Theobald and other potential malaria vectors were reduced in the pirimiphos-methyl trial area 2-35-fold more than in the area sprayed with DDT. Malariological indices were reduced by 65-68% in the pirimiphos-methyl sprayed area compared with only 26-35% reduction in the DDT sprayed area. Spraymen and villagers experienced no adverse side-effects from residual house-spraying with pirimiphos-methyl emulsion and it is concluded that this organophosphate product has advantages for malaria vector control, especially in operationally difficult situations.