# Scrub and murine typhus seroprevalence among blood donors in Laos

## TL;DR

This study found that scrub typhus and murine typhus are widespread in Laos, with higher exposure in northern provinces.

## Contribution

The study provides the first nationwide seroprevalence data for scrub and murine typhus among blood donors in Laos.

## Key findings

- STG seroprevalence was highest in northern provinces like Huaphan, Oudomxay, and Xiangkhuang.
- TG seroprevalence was found in both northern and southern provinces, including Oudomxay and Attapue.
- No significant association with age was found, but gender differences were observed for each infection.

## Abstract

Scrub typhus and murine typhus, caused by Orientia tsutsugamushi and Rickettsia typhi, respectively, are important causes of febrile illness in Laos. Although several studies have assessed rickettsial infection in selected provinces, the nationwide distribution remains unclear. This study aimed to estimate exposure to scrub typhus group (STG) and typhus group (TG) across twelve provinces of Laos and identify potential hotspots.

We screened 1,200 serum samples from blood donors (100 per province) for STG and TG IgG antibodies using enzyme-linked immunosorbent assays (ELISA). Samples with optical density ≥ 0.5 were confirmed by immunofluorescence assays (IFA).

Overall seroprevalence was 7.26% (95%CI:5.93-8.87) for STG and 4.09% (95% CI:3.11-5.37) for TG. STG seroprevalence was highest in Huaphan (27%), Oudomxay (19%) and Xiangkhuang (17%), all in northern Laos. TG seroprevalence was 10% in both Oudomxay (north) and Attapue (south). Compared with Vientiane Capital, these provinces had significantly higher seropositivity. No significant association was observed with age group. STG seropositivity was higher in males, whereas TG seropositivity was higher in females.

Rickettsial infections are widespread in Laos, with STG seroprevalence concentrated in the north and TG seroprevalence present in both the north and south, guiding future research priorities and informing targeted public health interventions.

Scrub typhus and murine typhus are caused by bacteria that can only survive inside cells, Orientia tsutsugamushi and Rickettsia typhi, respectively. These bacteria are transmitted to humans by arthropods: chigger mites for scrub typhus and fleas for murine typhus. Both diseases cause treatable fever, with symptoms ranging from mild to severe. Although exposure to these infections has been reported in Laos, most studies have been limited to central areas and a few provinces, which may not represent the entire country. This study investigated whether healthy blood donors across Laos had prior exposure to scrub typhus and murine typhus. We screened antibodies against both pathogens from 100 samples per province, collected from 12 provinces in Laos. We found that individuals in northern Laos, particularly in Huaphan, Oudomxay, and Xingkhuang, were more frequently exposed to O. tsutsugamushi compared to individuals in other provinces. In contrast, exposure to R. typhi was observed in both northern and southern Laos. However, no antibodies against scrub typhus were detected in our selected population in Salavan, despite the fact that previous studies of febrile patients have reported laboratory-confirmed infections, and no antibodies against murine typhus were found in Huaphan. This study suggests that scrub typhus and murine typhus are present throughout Laos, with varying patterns of exposure across different regions, although blood donors may be a low-risk population in terms of exposure.