Emergency control of Aedes aegypti as a disease vector in urban areas
Gratz, N.G.
Journal of the American Mosquito Control Association 7(3): 353-365
1991
ISSN/ISBN: 8756-971X PMID: 1791444 Document Number: 382373
The current world status of yellow fever, dengue and dengue haemorrhagic fever is briefly reviewed. More cases of yellow fever were reported to the WHO in 1986-88 than in any other 3-year period since reporting began in 1948, and there is a high risk of epidemics of all 3 diseases in many urban areas. The only effective way to prevent them is to control Aedes aegypti, the principal vector. Some recent community-based campaigns using larviciding and source reduction have managed to reduce Ae. aegypti populations, and such campaigns should be continued, but they cannot be relied upon to reduce populations low enough or fast enough to stop epidemics. It is argued that the only way to stop an epidemic is to kill the adult mosquitoes by space sprays. Nineteen trials of ULV (ultra-low volume) sprays and thermal fogs against Ae. aegypti, mostly in towns, are reviewed in detail and some others are mentioned. Aerial and ground ULV sprays of malathion at 400-1100 ml/ha have reduced biting rates by up to 99% for 2 weeks. Where dosages in this range failed there were other problems, such as high walls. Malathion at lower dosages (35-290 ml/ha) has generally failed to reduce biting rates enough to control dengue epidemics. Fenitrothion ULV at 500-1400 ml/ha, or 5-40 ml/house, has suppressed Ae. aegypti populations for 4-8 months. ULV sprays of chlorphoxim, naled, propoxur and resmethrin have also been tried with some success, but comparisons between insecticides and dosages are difficult because most trials have involved only 1 insecticide in 1 place at 1 or 2 dosages. The author concludes that "on the whole, there are enough instances where ULV applications have proved successful to justify use of the method for emergency control of Aedes vectors", but "trials should also be carried out with other insecticides and other dosage rates".J.E. Hudson Techniques for the emergency contol of adult A. aegypti populations and their development are reviewed. Larviciding and environmental measures provide only delayed control of adult populations. Large-scale field trials of the ultra-low volume application of insecticide concentrates in southeast Asia, South America and Africa, using aerial, ground, vehicle-mounted and hand-carried equipment, have, in most cases, resulted in satisfactory levels of control of adult populations. Sequential or indoor ULV applications of fenitrothion have provided immediate control and sustained reduction of the adult populations, often lasting well through normal peak transmission periods of dengue. Many ULV application trials in the Caribbean have not produced satisfactory control, but it is considered that this was due to the type of house construction, to the lower dosage rates of the malathion 96% ULV concentrates used, or to inappropriate droplet sizes. While ULV applications can provide rapid and effective emergency control of vectors at the same time of outbreaks of disease in urban and periurban areas, they should not be used as a routine mosquito control measure nor as an alternative to reducing vector populations by environmental measures.