Assessing the sociodemographic factors associated with Mycobacterium tuberculosis complex infection among free-ranging long-tailed Macaques in Thailand

The threat of disease transmission at the intersection of human-wildlife interfaces underscores the urgent need for detailed studies on the transmission of human-borne pathogens across species, especially among nonhuman primates in urban areas. This research focuses on the social and demographic determinants of Mycobacterium tuberculosis complex (MTBC) infection in free-ranging long-tailed macaques (Macaca fascicularis) in Thailand. Behavioral observations and non-invasive biological specimens (freshly defecated feces and rope-baited oral samples) were collected from 98 long-tailed macaques living in Wat Khao Thamon, southern Thailand, between August 2021 and February 2022. We detected the MTBC antigen using IS6110 nested-PCR method in 11 out of 98 monkeys (11.22%). Logistic GLMs revealed that the risk of MTBC acquisition was higher among macaques with frequent human-macaque interactions, whereas increased social grooming of conspecifics showed a trend toward reducing the risk. Our findings suggest that anthropogenic exposure increases the risk of MTBC infection among macaques, but this risk may be mitigated (socially buffered) by increased within-group affiliative interactions. More generally, the potential for increased disease prevalence in wildlife with frequent human interactions or reduced social buffering highlights the need to consider animal socio-demography when developing strategies to understand and prevent the transmission of diseases between humans and wildlife.

Methods
Our study involved behavioral observations and non-invasive biological sample collection of 149 adult long-tailed macaques from September 2021 to February 2022. We collected data using Samsung Galaxy Tablets and the HanDBase application. Observations were conducted by four trained observers for 6.5 hours daily, from Monday to Friday, following inter-observer reliability tests (Cohen’s kappa ≥ 0.85). Behavioral data were gathered through focal animal sampling, behavioral event sampling, and point-time scans.

Focal Sampling: We selected 101 animals based on their social interactions and followed them in 10-minute sessions using a randomized sequence. During each session, we recorded behaviors such as grooming, agonistic interactions, and self-scratching. After excluding three animals with insufficient data, we had 98 focal individuals (57 males, 41 females) with observation times ranging from 10.24 to 14.44 hours.

Behavioral Event Sampling: This method was used to record all instances of human-macaque interactions, including food provision, physical contact, and aggression, as well as any signs of sickness (e.g., coughing, changes in body condition). Focal sampling primarily captured monkey-monkey interactions, while event sampling data were used for analyses involving human interactions and clinical signs.

Non-Invasive Biological Sampling: Samples were collected using fecal swabs from freshly dropped feces and saliva samples from chewed, baited ropes. All samples were preserved in sterile lysis buffer and processed using a nested PCR method targeting the IS6110 sequence for detecting active MTBC infection. A total of 394 samples were analyzed from the 98 focal individuals.

This approach allowed us to gather comprehensive behavioral and health data while minimizing the impact on the natural behaviors of the macaques.