Malaria transmission in Tripura: disease distribution & determinants.

Background & objectives: Malaria is a major public health problem in Tripura and focal disease outbreaks are of frequent occurrence. The State is co-endemic for both Plasmodium falciparum and P. vivax and transmission is perennial and persistent. The present study was aimed to review data on disease distribution to prioritize high-risk districts, and to study seasonal prevalence of disease vectors and their bionomical characteristics to help formulate vector species-specific interventions for malaria control. Methods: Data on malaria morbidity in the State were reviewed retrospectively (2008-2012) for understanding disease distribution and transmission dynamics. Cross-sectional mass blood surveys were conducted in malaria endemic villages of South Tripura district to ascertain the prevalence of malaria and proportions of parasite species. Mosquito collections were made in human dwellings of malaria endemic villages aiming at vector incrimination and to study relative abundance, resting and feeding preferences, and their present susceptibility status to DDT. Results: The study showed that malaria was widely prevalent and P. falciparum was the predominant infection (>90%), the remaining were P. vivax cases. The disease distribution, however, was uneven with large concentration of cases in districts of South Tripura and Dhalai coinciding with vast forest cover and tribal populations. Both Anopheles minimus s.s. and An. baimaii were recorded to be prevalent and observed to be highly anthropophagic and susceptible to DDT. Of these, An. minimus was incriminated (sporozoite infection rate 4.92%), and its bionomical characteristics revealed this species to be largely indoor resting and endophagic. Interpretation & conclusions: For effective control of malaria in the State, it is recommended that diseases surveillance should be robust, and vector control interventions including DDT spray coverage, mass distribution of insecticide-treated nets/ long-lasting insecticidal nets should be intensified prioritizing population groups most at risk to avert impending disease outbreaks and spread of drug-resistant malaria.

Seasonal prevalence & resting behaviour of Anopheles minimus Theobald & An. fluviatilis James (Diptera: Culicidae) in east-central India.

Background & objectives: Anopheles minimus has recently been reported to have re-appeared in Keonjhar district of Orissa after a period of about 45 years of launching the malaria eradication programme. An. minimus and An. fluviatilis were the incriminated major malaria vectors in the district, endemic for falciparum malaria. The information on seasonal prevalence and resting behaviour of the vectors is crucial for implementing appropriate malaria control measures. Therefore, a study was undertaken on seasonal prevalence and resting behaviour of An. minimus and An. fluviatilis in this district. Methods: Seven randomly selected villages of Keonjhar district, Orissa, were studied during August 2005 to November 2007. Daytime resting collections indoors and outdoors were made covering three seasons of the year. The Anopheles mosquitoes obtained from different habitats were identified. Collections were maintained separately according to different sites as well as heights of the walls in human dwellings. Results: Among the indoor collections, the densities of An. minimus and An. fluviatilis were higher in human dwellings than cattle sheds. An. fluviatilis was the predominant (41.5%) species followed by An. minimus (26.3%) in human dwellings. The density of both the vector species in human dwellings peaked during rainy and winter seasons followed by summer. Walls were the most preferred site by these vectors for resting and the maximum number was collected at a height of 3 to 4 ft. Interpretation & conclusions: The resting behaviour of the vector species increases their contact with the sprayed walls and therefore, a quality residual spraying of human dwellings focusing indoor walls could interrupt the malaria transmission in this area.

STUDIES ON DISTRIBUTION AND BEHAVIOR OF ANOPHELES MINIMUS AND ITS ROLE OF MALARIA TRANSMISSION IN HAINAN PROVINCE AT PRESENT / 中国寄生虫学与寄生虫病杂志

Anopheles minimus was once a main malaria vector in Hainan Island and had been e-liminated basically through the campaign of indoor residual spraying launched in 1959. It again became an incriminated vector of some focal malaria outbreaks in recent years. The present study was conducted in a selected county-Danxian and a typical hilly area-Feibar in the west part of Danxian county in 1989-1990.An. minimus was found in 50% and 62. 5 % of the surveyed sites at mountainous and hilly area of Danxian county,but not found in coastal region. An. minimus was found in all 18 sites surveyed in Feibar district constituting 52% of anopheline composition. Man-biting rate made by human-baited collection was 3. 2 before midniaght and 38. 2 when collected through whole night in some sites. However, the behaviour characteristics of An. minimus has changed. It has become exophilic,exophagic, and has an equal preference for man and cattle. The vectorial capacity of An. minimus estimated by quantitative data was in accord with malaria infection rate in Feibar district ,and the malaria infection rate among the inhabitants in three types of residential quarter with different socioeconomic conditions. Malaria infection rates of residential quarter of land-reclamation outcomers, villagers and state farm residents were 10%,2. 9% and 0. 5% respectively during 40 days from July to August,1990.Owing to the fact that An. minimus has become a secondary vector only next to An. dirus, with a wide range of distribution and a considerable different characteristics in behaviour compared to that before spraying campaign , it is suggested that a malaria control programme must be seriously planned to adjust the new problem of malaria epidemiology in Hainan Province.