Malaria outbreak along the India-Bhutan border town of Saralpara, Assam, India.

Background & Objectives: A remarkable progress is being made in the South-East Asia region in reducing the burden of malaria. While all countries are committed to malaria elimination, continued transmission at and across international borders poses a threat to achieving this goal.

Methods: We investigated an outbreak of malaria in the India-Bhutan border area in a district of Assam state, India. A line listing of cases occurring during the outbreak period was made and a house-to-house survey was carried out to identify additional cases in the community. Entomological investigation consisted of light trap collection of vectors. Patients and health workers were interviewed to obtain information on the possible mode of transmission and ongoing inter-country collaboration across the border.

Results: Between October 21 to November 18 2022, 37 cases of malaria (all Plasmodium vivax), were diagnosed in Saralpara area of Kokrajhar district of Assam, bordering Bhutan. Of these four were diagnosed in Sarpang hospital, Bhutan. Median age was 20 years (range 3 to 70 years). Male to female ratio was 1:1.2. In addition, 6 individuals with asymptomatic malaria were detected in the community through an active case finding campaign. No cases were however reported on Bhutan side of the border. Anopheles culicifacies and An. annularis were identified from light trap collection. Saralpara is a remote and forested area where most of the residents are poor and engaged predominantly in farming activities. Being a harvesting season, they tend to stay overnight to protect their harvest from elephants. The health authorities in India and Bhutan exchanged information regularly at district-to-district level on the outbreak including through available and easy modes such as WhatsApp, telephone as well as electronic mail and collaborated in coherently implementing preventive measures on both sides and in managing the cases.

Interpretation & Conclusion: The outbreak of malaria in Saralpara demonstrates the risk of malaria outbreak in remote and forested areas, with possibility of spill over to the other side of the border. The fact that two countries had excellent inter-country cross-border collaboration and prior commitment thereby preventing further transmission of malaria to Bhutan can serve as a best practice for cross-border control of malaria and other communicable diseases.