# Gastrointestinal Parasitic Infections in Macaca fascicularis in Northeast Thailand: A One Health Perspective on Zoonotic Risks

## TL;DR

This study found high rates of intestinal parasites in macaques in Thailand, highlighting risks of zoonotic disease transmission to humans.

## Contribution

The study provides new insights into the diversity and prevalence of GI parasites in free-ranging macaques in Northeast Thailand.

## Key findings

- 86.5% of macaques were infected with at least one type of GI parasite.
- Strongyloides sp. and Balantioides coli-like were the most common parasites identified.
- Mixed infections with both helminths and protozoa were observed in 37.3% of cases.

## Abstract

Long-tailed macaques in Thailand often live close to humans in places like temples and parks. This close contact can increase the risk of spreading diseases, including intestinal parasites that affect both animals and people. In this study, we collected fecal samples from macaques in four provinces of Northeast Thailand and tested them using two laboratory methods. We found that most macaques (86.5%) were infected with at least one type of parasite. The most common parasites were Strongyloides sp. (a type of worm) and Balantioides coli-like (a protozoan). Some macaques were simultaneously infected with multiple parasites, which may reflect environmental burden and potential transmission complexity. This highlights the importance of monitoring macaque health and managing human–wildlife interactions to reduce disease risks.

Gastrointestinal (GI) parasitic infections in non-human primates are of growing concern due to their implications for both veterinary and public health. Long-tailed macaques (Macaca fascicularis), commonly found in peri-urban and temple environments in Southeast Asia, may act as reservoirs for zoonotic parasites, posing risks to humans and domestic animals. This study investigated the prevalence and species diversity of GI parasites in free-ranging macaques from four provinces in Northeast Thailand (Loei, Khon Kaen, Bueng Kan, and Sisaket). A cross-sectional study was conducted between April and May 2025. A total of 445 fecal samples were examined using two parasitological techniques: agar plate culture (APC) and the formalin–ethyl acetate concentration technique (FECT). The overall prevalence of parasitic infection was 86.5%, with Strongyloides sp. (65.2%) as the most prevalent helminth and Balantioides coli-like (29.5%) and Entamoeba histolytica-like (28.8%) as the predominant protozoa. Other parasites identified included helminths (Trichuris sp., Ascaris sp.) and protozoa (Blastocystis sp., Iodamoeba bütschlii, Entamoeba coli, and Chilomastix mesnili). Mixed infections were frequently observed, with both helminths and protozoa co-occurring in 37.3% of cases. The high infection rates and parasite diversity reflect substantial environmental contamination and sustained transmission cycles. These findings underscore the importance of integrated surveillance in wildlife populations and the need for One Health-based approaches to minimize zoonotic transmission risks at the human–animal–environment interface.