Insights into spatio-temporal dynamics of Anopheles vectors while approaching malaria elimination along the Thailand-Cambodia border.

Abstract

The international borders of Thailand are well recognized as areas with high malaria transmission risk. Although Sisaket Province, bordering Cambodia, is recognized as a malaria-prone area, major progress towards malaria elimination has been made. In fact, this province was ranked as having high malaria incidence in Thailand decades ago, increasing its potential for malaria re-introduction. To devise a re-introduction strategy, this work investigated the spatio-temporal dynamics of Anopheles and examined the malariogenic potential of villages in Sisaket Province. Human landing catches (HLCs) were recorded to collect adult mosquitoes from village and rubber-forest ecotypes between 18.00 and 06.00 hours. The collection was conducted for two years based on four consecutive nights per season in the rainy, cool-dry, and hot-dry seasons during July 2022-March 2024, for a total of 24 nights. Based on the results, Anopheles dirus s.s. was the primary malaria vector and predominant in the rubber-forest areas, where positive larval habitats were found. Its biting peaks were observed between 21.00 and 22.00 across seasons and years. The abundance of An. dirus was correlated positively with the amount of rainfall at two months (R = 0.89) and three months (R = 0.95) after the rainfall. Therefore, public health interventions to prevent outdoor biting should target rubber tappers and forest-goers two-three months after the rainy season. In addition, risk assessment of malaria re-introduction suggested a high potential based on the malariogenic potential scores. Thus, ongoing action is important to control any re-introduction to achieve sustainable malaria elimination in Sisaket Province.