Southeast Asia faces global change and emerging infectious diseases

Southeast Asia is undergoing major changes in land use affecting biodiversity, including growing urbanisation, increased livestock, the expansion of agricultural land, and the loss of forest cover, among others. What links are there between these changes and emerging zoonotic diseases and vector-borne infectious diseases?

The increasing emergence of infectious agents in human populations and the Covid-19 pandemic crisis show how important it is to understand the factors behind the emergence of zoonotic diseases (diseases for which the agent, a bacterium, virus or parasite, may also be passed from animals to humans). The same is true for vector-borne infectious diseases such as Chikungunya. That is the purpose of the ANR FutureHealthSEA¹ project, coordinated by Serge Morand, CNRS and CIRAD Senior Researcher. Scientists have developed retrospective models for the dynamics of epidemics, both internationally and in Southeast Asia, taking into consideration climatic factors and changes in land use.

To this end, they collected the available international data on the impact of infectious diseases in recent decades on humans and animals, as well as changes in land use, climate, biodiversity, and farming, along with a national data set from hospital monitoring of three major diseases through their cooperation with the Thai Ministry of Health. “These include dengue fever transmitted by mosquitoes, leptospirosis, caused by an environmental bacterium whose main reservoirs are rodents, and scrub typhus, caused by rickettsia (bacterium), whose vectors and reservoirs are mites”, explains Serge Morand. A series of texts on public policies and legal instruments was also created. This modelling effort seeks to provide a better understanding of epidemic dynamics in time and space with respect to interactions with socio-environmental factors.

10 years of collaborative research in Saen Thong

The project is based on the experience acquired in two ANR projects, as well as cooperation since 2012, with Thai scientists, communities, and local administrations in Saen Thong. “The demand to study various local issues, such as the exposure of livestock to pesticides, called for expertise in ecological sciences, human and health sciences, and the social sciences. In my opinion, such an interdisciplinarity approach was one of the project’s main achievements, and took concrete form with the creation of a socio-ecological observatory for biodiversity and health in Saen Thong”. It brings together research projects conducted under a One Health approach.

Studying the factors behind emerging infectious diseases

Based on data from the global infectious diseases and epidemiology network GIDEON, the team has seen an increase, during recent decades, in infectious epidemics within populations internationally. “Monitoring systems have enhanced detection capacity, but that does not explain such an increase,” stresses Serge Morand.

“Our research has shown, on a global scale, a correlation between expanded livestock breeding and increasing zoonotic and vector-borne infectious disease epidemics; and a correlation between the deforestation or extension of oil palm plantations and increasing epidemics in recent decades. It should be noted that countries with the lowest rate of biodiversity loss also have the lowest rate of epidemics, which suggests that biodiversity has a protective effect against epidemic risk.

In Thailand, commercial plantations appear to increase the risk of zoonotic and vector-borne disease epidemics such as dengue fever. Landscape fragmentation and climate variability, with El Niño / La Niña climate events, appear to encourage the growth of scrub typhus, while cattle density increases the risk of leptospirosis”, Serge Morand continues.

Protecting the health of ecosystems, animals and humans

The team stresses the importance of protecting ecosystems and the services they provide in reducing epidemic risks. It also emphasises the role of observatories in understanding the dynamics behind evolving health and environmental risks, as well as the implementation of nature-based solutions. In this respect, it is crucial to involve health and biodiversity actors in the field. Research will continue as part of the France 2030 PREZODE programme.