A spatio-temporal analysis of scrub typhus and murine typhus in Laos; implications from changing landscapes and climate.

Tamalee Roberts,Paul N Newton,Ivo Elliott,Daniel M Parker,Matthew T Robinson,Philip L Bulterys,Mayfong Mayxay,Sayaphet Rattanavong,Koukeo Phommasone,Stuart D Blacksell,Vilada Chansamouth,Nam-Hyuk Cho

doi:10.1371/journal.pntd.0009685

Abstract

BackgroundScrub typhus (ST) and murine typhus (MT) are common but poorly understood causes of fever in Laos. We examined the spatial and temporal distribution of ST and MT, with the intent of informing interventions to prevent and control both diseases.Methodology and principle findingsThis study included samples submitted from 2003 to 2017 to Mahosot Hospital, Vientiane, for ST and MT investigation. Serum samples were tested using IgM rapid diagnostic tests. Patient demographic data along with meteorological and environmental data from Laos were analysed.Approximately 17% of patients were positive for either ST (1,337/8,150 patients tested) or MT (1,283/7,552 patients tested). While both diseases occurred in inhabitants from Vientiane Capital, from the univariable analysis MT was positively and ST negatively associated with residence in Vientiane Capital. ST was highly seasonal, with cases two times more likely to occur during the wet season months of July-September compared to the dry season whilst MT peaked in the dry season. Multivariable regression analysis linked ST incidence to fluctuations in relative humidity whereas MT was linked to variation in temperature. Patients with ST infection were more likely to come from villages with higher levels of surface flooding and vegetation in the 16 days leading up to diagnosis.ConclusionsThe data suggest that as cities expand, high risk areas for MT will also expand. With global heating and risks of attendant higher precipitation, these data suggest that the incidence and spatial distribution of both MT and ST will increase.

Highlights

Scrub typhus and murine typhus are common causes of fever throughout Asia and are endemic in the Lao People’s Democratic Republic (Laos) [1,2]
With global heating and risks of attendant higher precipitation, these data suggest that the incidence and spatial distribution of both murine typhus (MT) and Scrub typhus (ST) will increase
The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Summary

Introduction

Scrub typhus and murine typhus are common causes of fever throughout Asia and are endemic in the Lao People’s Democratic Republic (Laos) [1,2]. Murine typhus (MT) has a much wider geographical distribution, known across all continents except Antarctica, but without estimates of global disease incidence [4]. MT is caused by the bacterium Rickettsia typhi and is transmitted by fleas, principally the rat flea Xenopsylla cheopis [4]. Both diseases are neglected with underestimated burdens on health, due in part to nonspecific symptoms and poor access to reference diagnostic assays. They can be treated with doxycycline, they result in severe disease and mortality in a significant minority [4]. We examined the spatial and temporal distribution of ST and MT, with the intent of informing interventions to prevent and control both diseases

Results

Discussion

Conclusion