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PHYSIOGRAPHIC AND ENTOMOLOGIC RISK FACTORS OF MALARIA IN ASSAM, INDIA

Fever surveys were conducted in several districts of the Indian state of Assam to ascertain the prevalence of malaria in relation to vector abundance, entomologic inoculation rates (EIRs), and geographic location of human settlements. Anopheles minimus were incriminated, but their relative abundance and biting rates varied among districts, and no significant correlation was observed between these two indicators (r = 0.43, P = 0.34). Plasmodium falciparum was the predominant parasite species except in two districts where P. vivax was the majority parasite. The EIRs per person/night were 0.46–0.71 in P. falciparum-predominant areas and 0.12 in the district where P. vivax predominated. The correlation of percentage of fever cases positive for malaria infection in each district with the corresponding EIR was not significant (r = 0.6, P = 0.21). Malaria cases were detected in all months of the year but peaked during May–June, which corresponded to the months of heavy rainfall. These were also the months with highest incidence of infection with P. falciparum. Malaria cases were observed in all age groups of both sexes, and there was clustering of cases in villages near the vector-breeding habitat (perennial seepage streams), and foothill villages. However, malaria incidences were consistently lower in villages within 5 km of the nearest health care facility, which were in town areas. The data presented are indicative of low-to-moderate levels of malaria transmission by An. minimus, and would be of value for developing future intervention strategies.

Received November 5, 2003. Accepted for publication March 29, 2004.

Acknowledgments: We are grateful to Dr. C. F. Curtis (London School of Hygiene and Tropical Medicine), Dr. R. Carter (University of Edinburgh), and the anonymous reviewers for their comments and advice on the manuscript. Thanks are also given to Dr. C. Lele (Pfizer, Ltd.) for statistical input and to the Assam Branch Indian Tea Association and State Health Directorate (Government of Assam) for logistics support in remote areas of the state. Technical assistance of the project staffs is gratefully acknowledged. Meteorologic data were obtained from the Regional Meteorological Centre, Guwahati (Assam). This study was presented at the Joint Malaria and Spring Meeting of the British Society of Parasitology held in Manchester (April 6–9, 2003) through the grant to Vas Dev by the Director General, Indian Council of Medical Research, New Delhi.

Authors’ addresses: Vas Dev and Sobhan Phookan, Malaria Research Centre (Indian Council of Medical Research), PO Sonapur, Kamrup, Assam 782 402, India, E-mail: mrcassam{at}hotmail.com. Vinod P. Sharma, Malaria Research Centre (Indian Council of Medical Research), 22 Sham Nath Marg, Delhi 110 054, India, E-mail: v_p_sharma{at}hotmail.com. Suraj P. Anand, Biometrics, DevOps-India (Pfizer Global R&D) 5, Patel Estate, S.V. Road, Jogeshwari (W), Mumbai 400 102, India, E-mail: surajanand{at}rediffmail.com.

Reprint requests: Vas Dev, Malaria Research Centre, PO Sonapur, Kamrup, Assam 782 402, India.