The risk of vector-borne disease exposure in rubber plantations of northern Lao PDR

Abstract

Unprecedented economic growth in South-East Asia has encouraged the expansion of rubber plantations. Outbreaks of vector-borne diseases occur in these plantations, yet data on the vector dynamics is limited. In this thesis I describe the mosquito ecology in rubber plantations compared to neighbouring habitats in northern Lao PDR, to assess the risk of vector-borne diseases for rubber workers and villagers, and to identify how to mitigate these risks.
I carried out a study to identify an ethically sound alternatives to human landing catches (HLC). The human-baited Double Net trap (HDN) collected similar numbers of Anopheles and Culex as HLC, but under-estimated the number of Aedes albopictus. As both HLC and HDN are crude ways of identifying the human-biting rate, the HDN is a representative method to estimate the human-biting rate outdoors without exposing collectors to mosquito bites.
Using the HDN, I compared the adult mosquito dynamics in the secondary forests, immature rubber plantations, mature rubber plantations and villages. A total of 113 species were identified, including 61 species not documented in Lao PDR before The highest number of mosquitoes were collected in the secondary forests. Three of the four most common species found were vector species; the dengue and chikungunya vector Ae. albopictus, the lymphatic filariasis vector Ar. kesseli and the JE vector Cx. vishnui. Additionally, in all habitats a daily exposure to malaria vectors was found.
To assess the risk of exposure to vector-borne diseases I explored the local human behaviour using sociological methods. Compared to staying in the village, dengue exposure risk increased when working in the plantations, which was exasperated when also living in these man-made forests. By contrast, malaria vector exposure risk decreased when living in the plantations.
I identified the characteristics of mosquito breeding sites in rubber plantations and villages. Aedes albopictus immature stages were most frequently collected from tyres and latex collection cups in the mature rubber plantations and from tyres and water containers (< and > 10 L) in the villages. A majority of the Cx. quinquefasciatus were collected from water containers (< and > 10 L) in the mature rubber plantations and villages. Anopheles dirus s.l. were mostly collected from puddles in the immature rubber plantations and villages.
This thesis emphasizes the importance of implementing mosquito control in the rubber plantations for the control of dengue disease. Larval control and personal protection methods are possible vector control methods for our study area. The successful implementation of vector control requires an inter-sectoral approach, with strong collaboration between the health sector, rubber industry and local communities.