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Microlevel epidemiological variations in designing malaria control strategies were studied. Quantitative and qualitative variations were observed between two physiographic zones and between four different ecotypes within the zones of the Koraput district. While the peak transmission occurred in rainy season in the 600 m plateau (Jeypore zone), the same was observed in cold season in 150 m plateau (Malkangiri zone). The age specific parasite prevalence indicated a high degree of transmission and high level of acquired immunity in top- and foot-hill villages of both zones as compared to plain and riverine villages. Transmission was perennial in top-hill and foot-hill villages while it was of short period (indicated by infant parasite rate) in others. Since the period and intensity of transmission vary, an uniform residual insecticidal spray schedule as followed at present is not necessary. Majority of fever patients in top-hill villages were positive for Plasmodium falciparum and therefore may be treated for malaria without slide collection and examination. Evaluations may be done by sample surveys. These steps can optimize the malaria control operation in the district.

P. falciparum schizonts were found in peripheral blood of six malaria patients including two infants who were moderately ill, with parasitaemia ranging from 33920 to 410800 per cubic mm. The patients lived in villages located at an altitude of 680 m and the phenomenon was observed during the cold season when transmission was high. Appearance of these forms was independent of host age.

A sample survey in 37 villages covering 10,733 people in 1986-87 in the Koraput district, Orissa showed that the malaria prevalence is of a much higher order than that reported by the National Malaria Eradication Programme (annual parasite incidence between 14.3 and 26.8 during 1981-86). Out of 833 positives detected 714 had Plasmodium falciparum, 86 had P. vivax, 12 had P. malariae and 21 had mixed infections. There were 650 asymptomatic parasite carriers and 127 gametocyte carriers. The infant parasite rate was 15.82 per cent and average enlarged spleen (AES) in 2 to 9 yr old children was 1.98. In a year round fever survey in 22 villages, 5520 blood smears were collected and 1364 were found positive for malaria, with 77.3 per cent P. falciparum. In a mass blood survey conducted in a labour camp at an irrigation project, 610 people were examined, and 181 were positive. Nearly 40 per cent of migrants and 22 per cent of locals were positive, P. falciparum being dominant.

A malariometric survey carried out among the upper Bonda tribals of Koraput district showed that malaria is the major cause of morbidity followed by worm infestation and malnutrition. A total of individuals 1,409 (32.2% of the population) were sampled and 771 were found positive for malaria parasites. Plasmodium falciparum was the predominant parasite (73.7%) followed by P. vivax (10.6%) and P. malariae (5.2%) among the positive cases. Mixed infection was observed in 10.5 per cent of positive individuals. The infant parasite rate was 60.0 per cent and the average enlarged spleen among the children between 2-9 yr was 2.11. The age specific parasite rate indicated high degree transmission and high level of acquired resistance among the tribals.

We report for the first time the detection of P. ovale infection in three patients in two hilly villages of Koraput district, Orissa state, India. The identification of the parasite was confirmed by the Imperial Colleage of Science and Technology, London.