Efficacy of Bacillus thuringiensis israelensis, VectoBac WG and DT, formulations against dengue mosquito vectors in cement potable water jars in Cambodia.

This study reports the evaluation of Bacillus thuringiensis israelensis (Bti), a biological larvicide, in cement jars holding river, well and rain water. Two Bti formulations, VectoBac WG and VectoBac DT, were evaluated in a village in Phnom Penh. Thirty-one households with cement jars supporting the colonization of Ae.aegypti immatures were chosen. In each house 3 jars were aligned next to each another and filled with the same type of water. One of the 3 jars was treated with VectoBac WG at 0.4 g per 50 liters, a second jar was treated with VectoBac DT at 1 tablet per 50 liters, and a third jar was an untreated control (UTC). The jars were not covered, kept outdoors and not subjected to water exchange activity. The efficacy of VectoBac to control natural Ae.aegypti infestation was measured by Ae.aegypti pupae surveillance, conducted 3 days per week for 3 months post-treatment (June-September 2004). All pupae were removed, allowed to emerge in the Cambodia National Malaria Center insectarium and the emerged adults were identified and counted. The VectoBac treatments were more effective in river water, followed by well and rain water. The VectoBac treatments significantly reduced the pupae numbers for a minimum of 3 months in the river water and 2.5 months in the well water (p < 0.05). In the rain water, the pupae densities in the VectoBac WG and DT treated jars were not significantly different from the untreated jars, although the treated jars yielded 2.0 to 5.2 fold less pupae, respectively, than in the untreated jars during the 3 months post-treatment. The efficacy of VectoBac WG to control Ae.aegypti was similar to the efficacy of VectoBac DT in the 3 water types (p > 0.05). It was also observed that VectoBac WG and DT were target specific, without any adverse effects on aquatic predatory insects common in well and rain water. VectoBac WG and DT were found to be easy-to-use formulations, with no need to repackage them prior to use in the containers. The amounts of VectoBac WG and DT used were 12.5 fold less by weight than temephos (Abate 1.0% SG).

Intestinal helminthic infections in schoolchildren in Cambodia.

During the period January to December 1998, the National Malaria Center (CNM) carried out a parasitological survey of schoolchildren in rural and semi-urban areas, to assess intestinal helminthic infections in schoolchildren in the central parts of Cambodia. In the rural areas, there were four schools in Stung Treng Province (all situated along the Mekong River), five schools in Kratie Province (around rubber plantations), six schools in Kampong Chhnang Province (along Tonle Sap Lake); and in the semi-urban areas, three schools in Beng Tumpon Commune and five schools in Chbar Ampeou Commune (Mean Chey District) were selected for study. By Kato-Katz technique, the prevalence of soil-transmitted helminthic infections in schoolchildren in both the rural and urban areas was high. The infection rate was between 10-40% for Ascaris, 2-17% for Trichuris and 5-65% for hookworm. Schistosomiasis and opisthorchiasis were found in the schoolchildren living along the Mekong River (Stung Treng Province); the infection rate of S. mekongi ranged from 12 to 43%. These infections in children were with hepatomegalies. An intervention in an urban area (Chraing Chamres) showed that after repeated treatment with mebendazole 500 mg single dose every 6 months, the prevalence of all parasites had dropped to about one third of the initial level.

Mekong malaria. II. Update of malaria, multi-drug resistance and economic development in the Mekong region of Southeast Asia.

In an expansion of the first Mekong Malaria monograph published in 1999, this second monograph updates the malaria database in the countries comprising the Mekong region of Southeast Asia. The update adds another 3 years' information to cover cumulative data from the 6 Mekong countries (Cambodia, China/Yunnan, Lao PDR, Myanmar, Thailand, Viet Nam) for the six-year period 1999-2001. The objective is to generate a more comprehensive regional perspective in what is a global epicenter of drug resistant falciparum malaria, in order to improve malaria control on a regional basis in the context of social and economic change. The further application of geographical information systems (GIS) to the analysis has underscored the overall asymmetry of disease patterns in the region, with increased emphasis on population mobility in disease spread. Of great importance is the continuing expansion of resistance of P. falciparum to antimalarial drugs in common use and the increasing employment of differing drug combinations as a result. The variation in drug policy among the 6 countries still represents a major obstacle to the institution of region-wide restrictions on drug misuse. An important step forward has been the establishment of 36 sentinel sites throughout the 6 countries, with the objective of standardizing the drug monitoring process; while not all sentinel sites are fully operational yet, the initial implementation has already given encouraging results in relation to disease monitoring. Some decreases in malaria mortality have been recorded. The disease patterns delineated by GIS are particularly instructive when focused on inter-country distribution, which is where more local collaborative effort can be made to rationalize resource utilization and policy development. Placing disease data in the context of socio-economic trends within and between countries serves to further identify the needs and the potential for placing emphasis on resource rationalization on a regional basis. Despite the difficulties, the 6-year time frame represented in this monograph gives confidence that the now well established collaboration is becoming a major factor in improving malaria control on a regional basis and hopefully redressing to a substantial degree the key problem of spread of drug resistance regionally and eventually globally.