Three case definitions of malaria and their effect on diagnosis, treatment and surveillance in Cox's Bazar district, Bangladesh.

In countries where malaria is endemic, routine blood slide examinations remain the major source of data for the public health surveillance system. This approach has become inadequate, however, as the public health emphasis has changed from surveillance of laboratory-confirmed malaria infections to the early detection and treatment of the disease. As a result, it has been advocated that the information collected about malaria be changed radically and should include the monitoring of morbidity and mortality, clinical practice and quality of care. To improve the early diagnosis and prompt treatment (EDPT) of malaria patients, three malaria case definitions (MCDs) were developed, with treatment and reporting guidelines, and used in all static health facilities of Cox's Bazar district, Bangladesh (population 1.5 million). The three MCDs were: uncomplicated malaria (UM); treatment failure malaria (TFM); and severe malaria (SM). The number of malaria deaths was also reported. This paper reviews the rationale and need for MCDs in malaria control programmes and presents an analysis of the integrated surveillance information collected during the three-year period, 1995-97. The combined analysis of slide-based and clinical data and their related indicators shows that blood slide analysis is no longer used to document fever episodes but to support EDPT, with priority given to SM and TFM patients. Data indicate a decrease in the overall positive predictive value of the three MCDs as malaria prevalence decreases. Hence the data quantify the extent to which the mainly clinical diagnosis of UM leads to over-diagnosis and over-treatment in changing epidemiological conditions. Also the new surveillance data show: a halving in the case fatality rate among SM cases (from 6% to 3.1%) attributable to improved quality of care, and a stable proportion of TFM cases (around 7%) against a defined population denominator. Changes implemented in the EDPT of malaria patients and in the surveillance system were based on existing staff capacity and routine reporting structures.

Susceptibility of the malaria vectors to insecticides in Bangladesh.

Insecticide susceptibility tests with diagnostic dosages of 4% DDT and 5% malathion concentrations conducted at field sites on the two important principal malaria vectors namely, Anopheles dirus and An. philippinensis have been reported. They are found to be susceptible to DDT and malathion. The implication of the use of insecticides in controlling malaria is also discussed.

A survey of larval and adult mosquitoes on the flood plains of Bangladesh, in relation to flood-control activities.

A mosquito survey was carried out between October 1991 and November 1992 on the flood plains of Bangladesh, as part of a baseline study designed to help predict the effects on vector-borne diseases of embanking rivers under the Bangladesh Government's Flood Action Plan. Overall, 15 species of larval and 15 species of adult anophelines were collected, along with 13 larval and 21 adult culicines. Anophelines made up only 6% of the mosquitoes caught at human bait. The most abundant anopheline biting man was Anopheles vagus, the dominant species in all nine sampling villages. The other recognized malaria vectors in the flood plains of Bangladesh, namely An. philippinensis, An. aconitus and An. annularis, were collected but in relatively low numbers. Culex vishnui was the most abundant biting culicine in all villages. Biting mosquitoes showed a bimodal seasonality of biting, with peaks between February and April and September and October. All biting mosquitoes showed a significant preference for outdoor biting. The densities of the mosquito populations are more likely to be affected by the large-scale environmental changes which have occurred in Bangladesh, as well as the dramatic increase in the density of the human population, than by the river embankments per se.

Incrimination of Anopheles aconitus Donitz as a vector of epidemic malaria in Bangladesh.

In 1989-91, post-monsoon epidemics of vivax malaria occurred in the central flood plain near Dhaka. Anopheles philippinensis, the usual vector in the paddy field habitat, was not present, but 1.4% of parous An. aconitus were infective. This is only the second time An. aconitus has been incriminated as a vector in Bangladesh. We speculate that the surprising increase in lowland malaria may have been caused by environmental change that favored the survival of An. aconitus.

Distribution and chromosomal polymorphism of the malaria vector Anopheles dirus species D.

Preliminary results indicate that species D of the Anopheles dirus complex is widespread west of the Thai-Burma border in Burma and Bangladesh. A chromosomal study of An. dirus species D in these areas has revealed that this malaria vector is highly polymorphic for chromosomal rearrangements in salivary gland polytene chromosomes. The data from the limited number of wild-caught samples suggest that different geographically isolated populations may occur with respect to the frequency of inversions 2La, 3Ra and 3La. The distribution of chromosomal polymorphisms may be associated with the geography and epidemiology of human malaria in this region.

Forest malaria in Bangladesh. I. Parasitology.

Malaria in the eastern forests of Bangladesh has never been controlled and has been the major source of the country-wide resurgence that has occurred since 1971. The malaria status of an isolated, forest-dwelling community was studied for 21 consecutive months. Blood examination, indirect hemagglutination testing, and detailed histories were used. Nearly 88% were found patent for Plasmodium falciparum and 70% for Plasmodium vivax at least once during the study. The population displayed characteristics of intense, annual transmission: asymptomatic patent infections, low trophozoite and gametocyte densities, and increasing antibody and decreasing parasite prevalence with advancing age. Prevalence and mean titer of antibody increased in each age group during the 7-month transmission season. Chloroquine-resistant P. falciparum was demonstrated epidemiologically.

Forest malaria in Bangladesh. II. Transmission by Anopheles dirus.

Seasonal, holoendemic malaria transmission in a small, isolated forest community was studied by doing outdoor and indoor all-night man-biting catches over 21 consecutive months. More than 3.8% of Anopheles dirus (=An. balabacensis s.l.), the most frequently caught anopheline, were infective. One An. annularis was also infective. Transmission occurred only during the 7-month monsoon. In the absence of DDT, An. dirus bit with equal frequency indoors and outdoors. When DDT was present in dwellings, fewer females fed indoors and they fed earlier. Feeding pattern was influenced by the phase of the moon: peak outdoors feeding was sharpest and earliest at first quarter and came later as the moon rose later. An average 31% of biting An. dirus lived long enough to reach infectivity of P. falciparum. Although fewer than 10 females fed per man per night, a resident could have received more than 100 infective bites in 2 years. Correlation between actual and calculated rates of gametocytemia were poorest in months when calculated survival rates of mosquitoes were most suspect.