The scope and limitations of insecticide spraying in rural vector control programmes in the states of Karnataka and Tamil Nadu in India.

The resurgence of malaria in India began in 1966 and the states of Karnataka and Tamil Nadu were no exception to this phenomenon. In both states the peak occurrence came in 1976. Malaria was largely confined to highly vulnerable and receptive areas. The problem of increased incidence was particularly associated with the development of several irrigation and hydro-electric schemes. Improperly maintained irrigation systems and reservoirs provided ideal breeding grounds. The present paper examines the scope and limitations of a major anti-malaria activity, namely residual insecticide spraying as adopted and practised in rural vector control programmes in irrigation development project areas. Past experiences (as during the National Malaria Eradication programme, 1958-1965) and current practices are reviewed on the basis of selected examples. Eradication programme, 1958-1965) and current practices are reviewed on the basis of selected examples. In view of the current re-emergence of the disease, the states are faced with new obstacles to residual insecticide spraying such as (a) the development of resistance of malaria vectors to DDT and other alternative compounds like BHC (benzene hexachloride), changing vector behaviour with avoidance of contact with indoor insecticide deposits on walls, (c) environmental contamination (risks of chemicals), (d) extensive use of insecticides and pesticides for crop protection under an expanding green revolution agricultural technology, particularly in irrigated areas and (e) the existence of outdoor resting populations of the major vector Anopheles culicifacies and their role in extra-domiciliary transmission, making residual insecticide spray less effective. Spraying operations are also hindered by the persistence of certain social and cultural factors. The custom of mud plastering, white-washing and rethatching rural houses, for example, results in the loss of insecticide-treated surfaces. Other outdoor rural activities persist as obstacles in attempts to break the transmission cycle; washing, bathing and sleeping outdoors; illegal fishing and woodcutting at night; poorly constructed make-shift structures;housing project labourers near water sources; cattle grazing in nearby forests and human population movements related to seasonal migrants. The chain and extent of the transmission is dependent upon the malaria parasite carriers in the community (both indigenous and imported types) and the degree of contact of the community with those sites where people carry on the above activities, and on the effectiveness of surveillance operations.