Relations between Anopheles darlingi breeding habitats, rainfall, river level and malaria transmission rates in the rain forest of Suriname.

Irregular peaks of P.falciparum malaria incidence were monitored in Suriname during 1982-86. An attempt is made to correlate these fluctuations of malaria rates with rainfall and river level in relation to the periodic availability of breeding habitats for the malaria vector Anopheles darlingi Root. Densities of adult female An.darlingi were recorded in the Upper-Marowijne region of Suriname, in a focus of malaria along the Marowijne River. Peaks in biting densities correlated well with periods of (i) high water level in the long rainy season, (ii) low water level in the long dry season, and (iii) abundant rainfall in the short rainy season. Critical levels of river-height and rainfall were defined which could explain most of the monthly fluctuations in malaria parasite incidence observed in this area.

[Epidemiology and control of malaria in Suriname]. / Epidemiología y control del paludismo en Suriname.

Malaria is endemic in the interior of Suriname, which is inhabited by descendants of black slaves and Amerindian tribes. Analysis of epidemiological data for the period 1965-1985 reveals that within that area malaria is endemic only in the territory of the Djuka Indians in the Upper Marowijne region. The endemicity may be due in part to the presence of a relatively large and stable population of the local vector, Anopheles darlingi, and also to the Djukas' frequent travels within their own territory. During 1985, transmission occurred year-round in only two of the many villages of the region, and the majority of cases were found in those same villages. Research following outbreaks of malaria in isolated villages in the plains region and the interior showed that the Djukas employed by the governmental services near these villages probably acted as partially immune carriers of the malaria parasites, transporting them from the reservoir to the villages where the outbreaks occurred. Recommendations are being formulated for the prevention and control of malaria in the interior of Suriname.

Epidemiología y control del paludismo en Suriname / Epidemiology and control of malaria in Suriname

El paludismo es endémico en el interior de Suriname, habitado por descendientes de esclavos negros y tribus amerindias. El análisis de los datos epidemiológicos del período 1965-1985 revela que en esa zona la malaria solo es endémica en el territorio de los djukas de la región del Alto Marowijne. La endemicidad puede ser en parte debida a la presencia de una población relativamente importante y estable del vector local. Anopheles darlingi, y también a los viajes frecuentes de los djukas en su propio territorio. En 1985, solo en dos de las muchas aldeas de la región hubo transmisión durante todo el año. En esas mismas aldeas se presentaron la mayor parte de los casos. Las investigaciones posteriores a los brotes de la malaria en aldeas aisladas de la región de sabana y del interior mostraron que los djukas empleados por los servicios gubernamentales cercanos a estas aldeas probablemente actuaron como portadores semiinmunes de los parásitos palúdicos desde el reservorio hasta las aldeas afectadas por los brotes. Se formularon recomendaciones para la prevención y el control de la malaria en el interior de Suriname

Epidemiology and control of malaria in Suriname.

Malaria is endemic in the interior of Suriname. However, epidemiologic data indicate that as of 1985 the only permanent malaria focus was located in an area along the Upper Marowijne River. The existence of this focal area can be accounted for partly by relatively high and stable numbers of the local malaria vector, Anopheles darlingi, in the region and also by frequent travels of local inhabitants within the Upper Marowijne region. Government workers from this area appear to have played a significant role in spreading malaria to other parts of the country.

Epidemiología y control del paludismo en Suriname / Epidemiology and control of malaria in Suriname

El paludismo es endémico en el interior de Suriname, habitado por descendientes de esclavos negros y tribus amerindias. El análisis de los datos epidemiológicos del período 1965-1985 revela que en esa zona la malaria solo es endémica en el territorio de los djukas de la región del Alto Marowijne. La endemicidad puede ser en parte debida a la presencia de una población relativamente importante y estable del vector local. Anopheles darlingi, y también a los viajes frecuentes de los djukas en su propio territorio. En 1985, solo en dos de las muchas aldeas de la región hubo transmisión durante todo el año. En esas mismas aldeas se presentaron la mayor parte de los casos. Las investigaciones posteriores a los brotes de la malaria en aldeas aisladas de la región de sabana y del interior mostraron que los djukas empleados por los servicios gubernamentales cercanos a estas aldeas probablemente actuaron como portadores semiinmunes de los parásitos palúdicos desde el reservorio hasta las aldeas afectadas por los brotes. Se formularon recomendaciones para la prevención y el control de la malaria en el interior de Suriname

Epidemiology and control of malaria in Suriname

Malaria is endemic in the interior of Suriname. However, epidemiologic data indicate that as of 1985 the only permanent malaria focus was located in an area along the Upper Marowijne River. The existence of this focal area can be accounted for partly by relatively high and stable numbers of the local malaria vector, Anopheles darlingi, in the region and also by frequent travels of local inhabitants within the Upper Marowijne region. Government workers from this area appear to have played a significant role in spreading malaria to other parts of the country

Epidemiology and control of malaria in Suriname

Malaria is endemic in the interior of Suriname. However, epidemiologic data indicate that as of 1985 the only permanent malaria focus was located in an área along the Upper Marowijne River. The existence of this focal área can be accounted for partly by relatively high and stable numbers of the local malaria vector, Anopheles darlingi, in the region and also by frequent travels of local inhabitants within the Upper Marowijne region. Government workers from this área appear to have played a significant role in spreading malaria to other parts of the country

Observations on the distribution of anophelines in Suriname with particular reference to the malaria vector Anopheles darlingi

A study was made on the distribution of anophelines in Suriname with special emphasis on the principal malaria vector Anopheles darlingi and on the occurrence of other possible vector species. Peridomestic human bait collections of adult mosquitoes and collections of larvae were made in many localities with a recent history of malaria transmission. Stable population of An. darlingi were only found in the interior, south of the limit of tidal influence, due to year-round availability of breeding habitats in quietly sunlit places in flooded forest areas and along river banks. In the area with tidal movement of the rivers, breeding is limited to flooded areas in the west season. Anopheles darlingi was only incidentally collected in low densities. In the interior, malaria transmission occurred in all places where An. darlingi was found. The absence of malaria transmission along the Upper Suriname River could be explained by the absence of An. darlingi. In the malaria endemic areas, An darlingi was the most numerous mosquito biting on man. In the tidal region, malaria outbreak are infrequent and might be explained by the temporary availability of favourable beeding habitats for An. darlingi. However, evidence is insufficient to incriminate an. darlingi as the vector of malaria in this region and the possible vectorial role of other anophelines is discussed

Observations on the distribution of anophelines in Suriname with particular reference to the malaria vector Anopheles darlingi.

A study was made on the distribution of anophelines in Suriname with special emphasis on the principal malaria vector Anopheles darlingi and on the occurrence of other possible vector species. Peridomestic human bait collections of adult mosquitoes and collections of larvae were made in many localities with a recent history of malaria transmission. Stable populations of An. darlingi were only found in the interior, south of the limit of tidal influence, due to year-round availability of breeding habitats in quiet partly sunlit places in flooded forest areas and along river banks. In the area with tidal movement of the rivers, breeding is limited to flooded areas in the wet season. Anopheles darlingi was only incidentally collected in low densities. In the interior, malaria transmission occurred in all places where An. darlingi was found. The absence of malaria transmission along the Upper Suriname River could be explained by the absence of An. darlingi. In the malaria endemic areas, An. darlingi was the most numerous mosquito biting on man. In the tidal region, malaria outbreaks are infrequent and might be explained by the temporary availability of favourable breeding habitats for An. darlingi. However, evidence is insufficient to incriminate An. darlingi as the vector of malaria in this region and the possible vectorial role of other anophelines is discussed.

Recent research on impregnated mosquito nets.

The present status of impregnated mosquito nets and other impregnated materials is discussed. Research projects which have produced most of the publications on this subject were conducted in areas in Africa with relatively high endemicity of malaria. In these areas, usage of impregnated mosquito nets caused substantial reductions in the sporozoite inoculation rates and some reduction in incidence of malaria attacks. However, there was little or no reduction in parasite rates in the human population. In several countries in Asia and the Pacific, vector control with impregnated mosquito nets has been introduced on a large scale, thus proving its affordability and compatibility with local customs in these countries. Substantial reductions in malaria parasite rates have been obtained in areas with low levels of malaria transmission. In order to develop the vector control method which is most appropriate for each area, much more research is needed on the technical and organizational aspects of vector control with impregnated mosquito nets. Examples are given of data already available as well as an indication of gaps in knowledge which still exist and will need more attention.

Efficacy of mosquito nets treated with permethrin in Suriname.

In the rain-forest of Suriname, where malaria is endemic, 95% of the Maroons (who call themselves bush-negroes) and all Amerindians use mosquito nets made of cotton cloth or, less frequently, nylon or cotton gauze over their hammocks or beds. Bush-negroes usually wash their nets weekly; Amerindians wash nets at 1-4 month intervals. Females of the principal local malaria vector, Anopheles darlingi Root, were seen blood-feeding through cotton cloth netting (at 22.30-23.30 hours) on a person sleeping in a hammock; others fed successfully after the net was opened in the morning. Cotton cloth impregnated with permethrin at a rate of 0.5 g/m2 killed all An. darlingi females exposed for 2 min, but after the material had been washed twice in soapy water the bioassay mortality fell to only 21.4%. Exit traps on a hut with a single sleeper protected by a permethrin-impregnated net yielded 185 An. darlingi females (12% blood-fed) in 74 nights, compared with 276 females (19% blood-fed) from another hut with a sleeper using an untreated net on the same nights (P less than 0.001). No An. darlingi females remained resting alive indoors in these huts during the daytime, and very few were found dead on the floor in the mornings (one treated, seven untreated). The 24 h mortality rate for those collected in exit traps was 58.4% for the test hut and 27.1% for the control hut (P less than 0.001). Bioassays of permethrin-treated cotton cloth using laboratory-reared sugar-fed Culex quinquefasciatus Say females showed that sprayed nets were less effective than nets impregnated by soaking (at equivalent dosages of 0.16-1.34 g/m2 measured by chemical assay) and confirmed that washing causes severe decline in insecticidal activity. The feasibility of local mass treatment of mosquito nets is discussed.

Biting and resting behavior of Anopheles darlingi in the Suriname rainforest.

An experimental hut study was conducted on the biting and house resting behavior of Anopheles darlingi in the rainforest of Suriname. Of all anophelines collected on human bait at indoor and peridomestic sites, An. darlingi comprised 100% and 98%, respectively. A single peak in biting activity occurred around 2300 h. With hourly exit trap collections, a peak of exit from the hut was observed at sunrise. Of these mosquitoes, 91% were freshly fed. The indoor resting period was calculated to be about 4 h. When the human bait in the hut was protected by a mosquito net, only 18% of the exiting mosquitoes were fed and the resting period was about 3 h.

Behavioral responses of Anopheles darlingi in Suriname to DDT residues on house walls.

A study was conducted in Suriname on the effects of DDT residual house spray on the main vector of malaria, Anopheles darlingi. Results obtained with an experimental hut sprayed with DDT wettable powder (2 g/m2 AI) were compared with results obtained with an unsprayed control hut. In the sprayed hut, entry rates were reduced by 32% and feeding success by 43.6%. The 24-h mortality of mosquitoes which entered the sprayed hut was 95% (range 85-100%) over the 10-month study period. After furnishing the sprayed hut according to local custom, no reduction in mortality was observed despite an abundance of unsprayed resting surfaces. Bioassays showed that the DDT deposits remained effective for at least 14 months. With excito-repellency test boxes an irritant effect caused by DDT on recently fed An. darlingi females was shown. With a choice-box experiment no preference for unsprayed over sprayed resting places could be demonstrated.

Epidemiology and control of malaria in Suriname

Malaria is endemic in the interior of Suriname. However, epidemiologic data indicate that as of 1985 the only permanent malaria focus was located in an area along the Upper Marowijne River. The existence of this focal area can be accounted for partly by relatively high and stable numbers of the local malaria vector, Anopheles darlingi, in the region and also by frequent travels of local inhabitants within the Upper Marowijne region. Government workers from this area appear to have played a significant role in spreading malaria to other parts of the country

Published in Spanish in Bol. Oficina Sanit. Panam 111(6):497-511, 1991