Malaria varies with the type of parasite or vector involved, the level of resistance and eco-epiderniological considerations:

TRibAL MALARIA Generally prevalant in the tribal areas of deep forests, forest-fringes (subtype 1) and surrounding ecologically disturbed areas (subtype 11), it poses a management problem due to poor health infrastructure and inadequate drugs. P falciparum is predominant with multiple drug resistance; deaths are common. Subtype 11 regions are prone to epidemics due to population migrations. According to NMEP data, tribal areas, with about eight per cent of the total Indian population, account for 39 per cent of all malaria cases and 68 per cent of P faiciparum cases in the country.

RURAL MALARIA Moderately endemic in the irrigated areas of and and semi-arid plains (subtype 1), rural malaria has a predominance of P vivax. Widespread vector resistance to multiple insecticides and localised parasite resistance to chloroquine pose problems for the moderately developed health infrastructure. Poor irrigation, water-logging, seepages from canals and poor drainage systems are responsible for the increase of malaria. The rural areas around the Upper Krishna Irrigation project in Karnataka, Sardar Sarovar Dam in Gujarat and the Indira Gandhi Canal in Rajasthan have witnessed outbreaks recently.

URBAN MALARIA Towns and cities (subtype 1) are mode- rately endemic with P vivax predominance and focal incidence of P falciparum. Sporadic epidemics occur, especially around construdioq projects. The main vectors are An stephansi and An culicitacies. Sub-urban and per-urban areas (subtype 11), with unplanned settlements, slums and poor sanitary conditions are prone to epidemics and deaths due to P falciparurn infection.

INDUSTRIAL MALARIA Development projects are highly prone to malaria epidemics resulting from drug resistant parasites, one or more vectors refractory to transmission control and limited health infrastructure. NMEP data clearly shows that the construction of the Mirzapur thermal power project, Uttar Pradesh (UP), saw a five-fold increase in malaria incidence in the district in 1980. The Mathura oil refinery and the National Thermal Power Corporation unit in Dadn also contributed to the rise of malaria incidence in UP.

BORDER MALARIA Mainly caused by migrations across international borders, this type cuts across all epidemiological boundaries and often contributes new and drug resistant parasite strains. Migration even within the country complicates the epidemiological classification. Kondrashin, a WHO malaria expert, estimated in 1991 that about one- sixth of India's population moves annually during the transmission season from non-malarious areas to malarious areas and vice versa.