Comparison of Plasmodium falciparum infectivity to Anopheles dirus D using direct and indirect blood feeding methods

Membrane feeding method (indirect blood feeding) using defibrinated blood has been established and was found to be as good as the direct feeding method with no singificant differences in the production of oocysts and sporozoites in Anopheles dirus D (p > 0.05). However, lsuccessful feeding was greater in the direct feeding method (69.4 per cent) when compared to the membrane feeding method (46.7 per cent) (p <0.0001). Based on 19 malaria patients who had > 400 gametocytes per ul of blood, the effect of antimalarial drugs on oocyst and sporozoite rates was also studied and it was found that mefloquine treated patients produced reduced infection and infectivity in an. dirus D than those who received antimalarial drugs other than mefloquine. Patients who had gametocytes and have been treated for causes other than malaria and who did not receive any antimalarial drugs were found to produce the highest infection and infectivity rates in An. dirus D (p < 0.0001).

Rapid and efficient removal of immature Aedes aegypti in metal drums by sweep net and modified sweeping method.

A modified sweeping method was developed using a cotton sweep net for control of Ae. aegypti immatures in 200 liter (44 gallon) metal drums which are major sources of breeding in Yangon. Laboratory experiments revealed that with only 4 sweeps (approximately 10 minutes duration), the mean % removal (+/- SD) of Ae. aegypti fourth stage larvae was 88.5% +/- 1.47. This was followed by a field study undertaken in Sanchaung township, Yangon. Twenty-eight drums with moderate (< 500 immatures) to high (> or = 500 immatures) Ae. aegypti density were tested in the field. It was found that with only 4 sweeps per drum, a total of 24,886 immatures were removed out of 29,155 immatures in these 28 drums, giving a mean % removal per drum of 85.36% +/- 10.74 (range = 55.54-98.62%). This sweeping method is simple, cost-effective, and readily accepted by the community. It could be an appropriate technology for control of the dengue hemorrhagic fever (DHF) vector Ae. aegypti.

Malaria Situation in a Forested Foot-hill Area of Myanmar

Entomological survey was carried out during July 1987 in a forestedfoot hill teak plantation area Tha-bye-wa village, Oktwin Township, Pegu Division. At the same time, thick and thin blood films were taken and spleen rate determined in children. The parasite rate for children under 10 years of age was 66.7

(16/24) and the infant parasite rate was 50

(2/4). The spleen rate for children 2-9 years age group was found to be 88.2

(15/17). The anopheline fauna collected was mostly made up of An. dirus, An.minimus, An. tessalatus, An. minimus was found to have occysts and one An. vagus collected biting man had sporozoites in the salivary glands. Two species of mosquitoes were also recorded for the first time in Burma. The epidemiological pattern of malaria transmission in the area and possible methodologies for control in such areas are discussed.

Anophiline mosquitoes of Myanmar. 2: Anopheles (Cellia) minimus Theobald, 1901

Anopheles minimus together with Anopheles dirus consitute the primary vectors of malaria in Myanmar. The former has a wider distribution and occurs in higher densities with longer seasonal prevalence and is therefore considered to be the most important malaria vector in the country. Previous studies showed that An.minimus breeds in grassy edges of perennial hill streams, in slow running irrigation channels and terraced rice field while DMR teams, in addition, found it breeding in small puddles in stream beds together with An. maculatus. At Phado, An. minimus was found to constitute 26.2 per cent, 50.5 per cent and 44.1 per cent in monsoon, cool/dry hot/dry seasons respectively.Prevalence of An.minimus in relation to distance from forest was presented. Biting, resting behaviour and host preference studies were carried out and results presented. Man-biting rate and vectorial capicities in relation to rainfall for each month over a year are also presented.

Anopheline mosquitoes of Myanmar. 1: Anopheles (Cellia) dirus Peyton and Harrison, 1979

Results of the study involving distribution, breeding habits, biology under laboratory cinditions, adult bionomics and its relationship to malaria transmission under different ecological condition have been studied and presented. Cytogenetics and iso-enzyme studies to differentiate its sibling species were also presented. Of the sibling species of An.dirus, species D was found to predominate in Myanmar, whereas species A was recorded from Central Burma. Susceptibility of An.dirus to DDT and Bacillus sphaericus was also reported.