Preliminary report on the effect of selective application of propoxur on indoor surfaces in El Salvador
Lassen, K.; Liu, S.Y.; Lizarzaburu, C.; Ríos, R.
American Journal of Tropical Medicine and Hygiene 21(5): 813-818
1972
ISSN/ISBN: 0002-9637 PMID: 5074694 Document Number: 53463
Anopheles albimanus Wied. has become resistant to DDT in many parts of Central America, where it is the main vector of malaria. A promising substitute for DDT is propoxur. In 1966-69, this had given encouraging results when applied every 3 months at 2 g/m2 to all interior surfaces of houses in La Union, El salvador. However, for several reasons it was considered that application of lower dosages to selected surfaces at shorter intervals might be at least as successful. Amongst these reasons were the facts that substantial renovation of about a third of the houses takes place each year, leading to a loss of the insecticide deposits, that temporary housing is built by migrant workers during the cotton harvest and may escape treatment, that propoxur is relatively volatile, with a half-life of 2 weeks at 25 deg C and that the vapour is toxic to mosquitos. After preliminary observations in 1969-70 had shown that females of A. albimanus entering a house moved freely over the wall and roof surfaces and remained within for several hours, a field trial was started in February 1970 in an area of about 500 km2 in La Paz, El Salvador, Containing 30 000 inhabitants and 7000 dwellings. Propoxur was applied every 35 days to all dwellings at a rate of about 60 g each by spraying swaths on the inner side of the roof and in the angle between the roof and the walls, The results are being assessed by catches of adult mosquitos and by routine examination of blood-smears from the inhabitants. According to mass-surveys carried out in 1971, the incidence of malaria in the trial area has been reduced to one tenth of that in an untreated area used for comparison. The cost of these measures was only about half that of the full spraying carried out in 1966-69. In the course of mosquito surveys, adults of A. albimanus resistant to propoxur were discovered in a small area where that insecticide had not previously been used in anti-malaria operations, though carbamates had been used on crops in previous years.