Environmental changes and risk of plague epidemics in Indonesia

Historical epidemiological data indicate that plague epidemics caused thousands of deaths in Indonesia between 1911 and 1956. During this period, silent phases of the disease were observed, followed by re-emergences several years or even decades later in certain regions. The Indonesian government, both at the regional and central levels (notably the Ministry of Health of the Republic of Indonesia), has undertaken decades of epidemic management efforts, including plague surveillance, medical treatments, vector control, and improvements in individual and environmental sanitation. There were a few sporadic outbreaks in 1968, 1987, and 2007. Since then, no further cases have occurred, but this could just be another silent phase.

A literature search comprising articles and reports including published and unpublished dissertations, was performed using the PubMed online database, the Directorate General of Disease Prevention and Control, the Ministry of the Health Republic of Indonesia, Institute for Vector and Reservoir Control Research and Development, The Ministry of Health of Indonesia, Provincial Health Offices, Google Scholar, Science Direct, Medicus Index for the Southeast Asian Region (IMSEAR) and co.IMSEAR), and others. All literature referring to plague in Indonesia (1923-2019) was used as a reference for this article. The Global Land Cover 1992-2020 from the European Space Agency database was used to monitor land cover changes with a spatial resolution of 300 meters. The Esri Sentinel-2 Land Cover Explorer database, created by ESRI (Environmental Systems Research Institute, Redland, California, USA) using Sentinel-2 satellite imagery was also used. This database shows global land cover change between 2017 and 2023, using only 2023 data. Seven land cover classes were identified: Water, Forest, Flooded fields, Fields, Urban, Bare ground, and Pasture.

Environmental changes, essentially land conversion, have occurred in regions where plague outbreaks were previously recorded, with the exception of Eastern Java. Land conversion, increased human population density, and the heightened risk of human-rodent interactions could contribute to a resurgence of plague epidemics in Indonesia. Vectors and rodent hosts of Yersina pestis are still present in all regions but one with a higher human population density and thus a higher risk of contact. In Eastern Java, the environment remained the same as when plague outbreaks previously occurred.

We conclude that the historical areas of plague outbreaks have a potential for silent periods of plague transmission which could last decades. Furthermore, land conversion and the development of human settlements in these regions have led to a higher human presence, thus potentially increasing the risk of contact and transmission. There is therefore today a risk of plague resurgence in Indonesia and the current plague-free period might just be a silent period. In order to prevent outbreaks of plague after a period of silence and to implement an early alert system of plague transmission from animals to humans via fleas, the monitoring of potential Y. pestis circulation in sylvatic areas also needs to be intensified.