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. 2026 Jul 8;12(4):e71070. doi: 10.1002/vms3.71070

Gastrointestinal Parasites of Free‐Ranging Rhesus Macaques (Macaca mulatta) in Kathmandu: A One Health Perspective on Shared Environmental Risks

Yashoda Khadka 1,✉, Ananta Dahal 1, Sujan Adhikari 1, Akash Adhikari 2, Aarati Sigdel 1, Chet Raj Pathak 1,✉
PMCID: PMC13344679  PMID: 42418300

ABSTRACT

Background

The increasing interface between human and non‐human primate populations in urban centres presents a shared environmental health risk. This risk is particularly prominent at religious sites where close interactions are culturally motivated.

Objectives

This study aimed to determine the prevalence and diversity of gastrointestinal (GI) parasites in free‐ranging rhesus macaques (Macaca mulatta) at two UNESCO World Heritage sites in Kathmandu, Nepal.

Methods

An opportunistic, non‐invasive cross‐sectional study was conducted in July and August 2024. Freshly voided faecal samples (N = 105) were collected from macaques at Pashupatinath Temple (n = 45) and Swayambhunath Stupa (n = 60). The samples were processed using standard coprological techniques, including zinc sulphate flotation and sedimentation, for microscopic examination.

Results

The overall prevalence of GI parasites was 77.1% (81/105). Nine genera were identified, comprising four protozoans and five helminths, eight of which contain species with recognized zoonotic potential. The most prevalent parasites were Entamoeba sp. (37.1%), Strongyle‐type eggs (25.7%), and Strongyloides sp. (20.0%). Double infections were the most frequent pattern (41.0%).

Conclusions

The high burden of potentially zoonotic parasite genera in macaques at these popular international sites highlights substantial environmental contamination and a shared exposure risk at the human–macaque interface. These findings underscore the urgent need for integrated sanitation, public awareness, and management strategies guided by a One Health framework.

Keywords: environmental contamination, gastrointestinal parasites, Macaca mulatta, One Health, urban‐wildlife interface

Free‐ranging rhesus macaques at Kathmandu's UNESCO heritage sites exhibit a 77.1% prevalence of potentially zoonotic gastrointestinal parasites. These findings highlight significant environmental contamination and a shared exposure risk, emphasizing the critical need for integrated One Health management strategies at the urban human‐wildlife interface.

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1. Introduction

Rhesus macaques (Macaca mulatta) are a highly adaptable primate species distributed widely across Asia. They frequently inhabit areas in close proximity to human populations, particularly around religious and cultural sites where macaques live in commensal association with humans (Cooper et al. 2022). In the Kathmandu Valley of Nepal, over 1000 rhesus macaques are estimated to reside within temple precincts (Adhikari et al. 2023). Mainly these monkeys depend on food provisioning from devotees and share a common space with thousands of daily visitors (Tandan et al. 2023). Such intensive human–macaque interactions therefore create complex ecological and epidemiological interfaces (Hasan et al. 2013; Rittem et al. 2024).

The close association between humans and rhesus macaques raises important public health concerns regarding shared environmental exposure and the potential for cross‐transmission of zoonotic pathogens. Non‐human primates (NHPs) can serve as reservoirs for pathogens that infect humans, including gastrointestinal (GI) parasites (Rondón et al. 2024). Many of these parasites (e.g., Giardia duodenalis, Entamoeba histolytica, Cryptosporidium spp.) are capable of cross‐species transmission where infected and healthy individual share common resources (contaminated food, water, soil, fruits) and even contact points (Carrillo‐Bilbao et al. 2021; Mapagha‐Boundoukou et al. 2024). The transmission of these parasites is typically facilitated by conditions of poor sanitation and environmental contamination (Moloi 2024; Sanhueza Teneo et al. 2025). In urbanized settings, where human and macaque densities are high, the risk of parasite transmission is therefore further amplified.

Parasites harm the health of their hosts, influence the population size, and affect how different species interact within a community (Buck 2019; Kaminsky and Mäser 2025). When parasites cross species boundaries, they can cause significant morbidity manifesting parasite specific complications (Hananeh et al. 2022). Several GI parasites of public health concern such as nematodes (hook worms, Ascaris, Strongyloides), cestodes (Taenia), and protozoa (Giardia, Entamoeba) are more evident in these shared environments (Adrus et al. 2019; Tandan et al. 2023; Adhikari et al. 2023).

GI parasites can cause a range of debilitating conditions in both NHPs and humans. Protozoan infections, particularly Entamoeba histolytica and Giardia duodenalis, are frequently associated with acute gastroenteritis, manifesting as severe diarrhoea, abdominal cramps, and dehydration. In severe cases, amoebiasis can lead to dysentery and extra‐intestinal abscesses (Braseth et al. 2021; Levecke et al. 2015). Among helminths, Strongyloides spp. can induce cutaneous larva migrans and respiratory distress during larval migration, while heavy intestinal burdens of Ascaris sp. and Trichuris sp. are linked to malnutrition, stunted growth, and intestinal obstruction, particularly in children and young macaques (Alshami and Wadhwa 2025; Chhetala et al. 2025; Maxfield and Crane 2025). These shared clinical manifestations highlight the direct health risks posed by a highly contaminated shared environment.

Although there have been parasitological studies on Nepalese primates, current data remain limited. Few studies have specifically focused on rhesus macaques at major temple complexes in the Kathmandu Valley (Adhikari et al. 2023; Chhetala et al. 2025; Tandan et al. 2023). Previous studies in Nepal have reported variable prevalence rates, with protozoan infections ranging from 13% to 40% and helminths often exceeding 50% in urban macaque populations (Adhikari et al. 2023; Chhetala et al. 2025; Tandan et al. 2023). However, most of them lack detailed assessments of parasite diversity, site‐specific differences, and patterns of co‐infection. Such knowledge gaps consequently hinder effective wildlife management and public health planning.

The present study was designed to address these gaps by conducting a systematic survey of GI parasites in rhesus macaque populations at two prominent sites: the Pashupatinath Temple and the Swayambhunath Stupa of Kathmandu, Nepal. In addition, this study aimed to quantify overall and site‐specific parasite prevalence, document the diversity of parasite taxa present, and characterize infection patterns, including single and multiple infections. While relying on conventional morphological diagnostics, these updated and detailed parasitological data provide a critical, current baseline for the continuous monitoring of these heavily trafficked interfaces. This informs evidence‐based wildlife management strategies, public health interventions, and lays the essential groundwork for future molecular epidemiological studies. The outcomes will support the development of policies that mitigate shared environmental risks at Kathmandu's UNESCO sites.

2. Materials and Methods

2.1. Study Area

This study was conducted at two prominent religious and cultural sites within the Kathmandu Valley, Nepal: the Pashupatinath Temple and the Swayambhunath Stupa (Figure 1). Both are UNESCO World Heritage sites and attract large numbers of domestic and international visitors daily. The Pashupatinath area lies approximately 5 km northeast of Kathmandu city centre (27°42′N, 85°21′E; 1300 m elevation), while the Swayambhunath complex popularly known as the ‘Monkey Temple’ is located on a hilltop in the western part of the city (27°71′N, 85°29′E). Both sites are urban green spaces embedded within densely populated areas and sustain substantial populations of free‐ranging rhesus macaques, estimated at ∼300 individuals in Pashupatinath and ∼400 in Swayambhunath (Adhikari et al. 2023).

FIGURE 1.

FIGURE 1

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Map of the Kathmandu Valley, Nepal, showing the locations of the two study sites: Pashupatinath Temple and Swayambhunath Stupa.

2.2. Sample Collection and Preservation

An opportunistic, non‐invasive cross‐sectional survey was carried out during the monsoon season months of July and August 2024. In total, 105 freshly voided faecal samples were collected: 60 from Swayambhunath and 45 from Pashupatinath, representing ∼15% of the estimated macaque populations. This sample size served as a pragmatic maximum target designed to capture a representative fraction of the population within the logistical and temporal constraints of the monsoon season. Sampling was performed during 06:00 AM–10:00 AM because this window aligns with peak morning foraging and subsequent defecation behaviours, maximizing the likelihood of collecting freshly voided faeces. To minimize pseudo‐replication, sampling was conducted by moving systematically through the temple complexes, targeting spatially distinct troops. Individual macaques or groups were observed from a distance until defecation occurred, and samples were only collected following visually confirmed, separate defecation events. For the purposes of this study, ‘fresh’ faeces were strictly defined as those being visually moist, intact, and collected within approximately 5 min of voiding. Approximately 10 g of faeces was collected with sterile spatulas into labelled zip‐lock bags. Field personnel utilized standard biosafety precautions, including disposable gloves and face masks, during all collection and handling procedures. Because the study relied entirely on non‐invasive environmental sampling without any direct animal contact or disturbance, formal ethical approval for animal handling was not required, though all procedures strictly adhered to temple regulations. Samples were preserved with 10% formalin and transported in a cool box to prevent the degradation of parasitic elements.

2.3. Laboratory Examination

Parasitological analyses were performed at the Veterinary Parasitology Laboratory, Faculty of Animal Science, Veterinary Science and Fisheries, Agriculture and Forestry University, Rampur, Chitwan. Two complementary concentration techniques were used to maximize parasite detection.

2.3.1. Zinc Sulphate Flotation Technique

Approximately 3 g of faeces was homogenized in water, filtered through a tea strainer, and centrifuged at 1500 rpm for 5 min. The pellet was resuspended in saturated zinc sulphate (ZnSO4; specific gravity 1.18) and centrifuged again. A coverslip was placed on the meniscus, removed after 5–10 min, mounted on a slide with methylene blue, and examined microscopically (100× and 400×). This technique is particularly effective for protozoan cysts and nematode eggs.

2.3.2. Sedimentation Technique

The residual sediment after flotation was collected, centrifuged at 1500 rpm for 2–3 min, and the supernatant was discarded. This washing and centrifugation process was repeated until the supernatant became clear. The final sediment was resuspended, mixed with a drop of Lugol's iodine, and examined microscopically at 100× and 400× magnifications for the detection of heavier parasite eggs such as trematodes that do not float readily.

2.3.3. Parasite Identification

Parasite cysts, eggs, and oocysts were identified to genus level based on morphology, size, and structural features, with reference to standard parasitological keys (Soulsby 1982; Zajac and Conboy 2012). Representative photomicrographs of the detected parasites are shown in Figure 2.

FIGURE 2.

FIGURE 2

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Representative photomicrographs of parasite genera identified in rhesus macaques: (1) Entamoeba sp. cyst, (2) Giardia sp. cyst, (3) Balantidium coli cyst, (4) Eimeria sp. oocyst, (5) Strongyle‐type egg, (6) Strongyloides sp. egg, (7) Trichuris sp. egg, (8) Taenia sp. egg, and (9) Ascaris sp. egg. For panels 2, 4, 5, 6, and 7, scale indicates length; for panels 1, 3, 8, and 9, scale indicates diameter.

2.4. Statistical Analysis

The data were entered in Microsoft Excel 2016. Prevalence was calculated as the number of positive samples divided by the total number of samples examined, expressed as a percentage. A chi‐square (χ 2) test was applied to compare prevalence between study sites, with significance set at p < 0.05.

3. Results

3.1. Prevalence of Helminth Parasites

Among 105 faecal samples analyzed, 81 tested positive for at least one GI parasite, and nine genera of parasites were identified: four protozoa and five helminths (Figure 2).

Protozoan infections occurred in 57.1% of the macaques and helminth infections in 55.2% of the macaques (Table 1). The most frequent was Entamoeba sp. (37.1%), followed by Strongyle‐type eggs (25.7%) and Strongyloides sp. (20.0%). Less common were Giardia sp. (13.3%), Balantidium coli (9.5%), Ascaris sp. (7.6%), Trichuris sp. (7.6%), Taenia sp. (5.7%), and Eimeria sp. (3.8%). The overall prevalence of GI parasites was 77.1% (95% CI: 68.0–84.7). At Swayambhunath, 47 of 60 samples (78.3%; 95% CI: 65.8–87.9) were positive, while 34 of 45 samples at Pashupatinath (75.6%; 95% CI: 60.5–87.1) harboured parasites. The difference was not statistically significant (χ 2 = 0.114, df = 1, p = 0.735).

TABLE 1.

Prevalence of gastrointestinal parasite genera in rhesus macaques among the total sample (N = 105) from the Swayambhunath (n = 60) and Pashupatinath (n = 45).

Prevalence of GI parasites
Group of parasite Parasite species Swayambhunath, n (%) Pashupatinath, n (%) Overall, n (%)
Protozoa Entamoeba sp. 25 (41.7) 14 (31.1) 39 (37.1)
Giardia sp. 9 (15.0) 5 (11.1) 14 (13.3)
Balantidium coli 6 (10.0) 4 (8.9) 10 (9.5)
Eimeria sp. 3 (5.0) 1 (2.2) 4 (3.8)
Overall protozoa 38 (63.3) 22 (48.9) 60 (57.1)
Helminth Strongyle‐type 17 (28.3) 10 (22.2) 27 (25.7)
Strongyloides sp. 13 (21.7) 8 (17.8) 21 (20.0)
Ascaris sp. 5 (8.3) 3 (6.7) 8 (7.6)
Trichuris sp. 5 (8.3) 3 (6.7) 8 (7.6)
Taenia sp. 4 (6.7) 2 (4.4) 6 (5.7)
Overall helminth 35 (58.3) 23 (51.1) 58 (55.2)
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Note: Percentages may not sum to totals due to co‐infections.

3.2. Infection Complexity and Polyparasitism

Polyparasitism was a prominent finding. Of 81 infected macaques, 63.0% harboured more than one parasite genus. Across the full population (N = 105), 22.9% were negative, 28.6% had single infections, 41.0% had double infections, and 7.6% had triple infections (Figure 2).

4. Discussion

Our results reveal a heavy burden of GI parasites among free‐ranging rhesus macaques at two major urban temple sites in Kathmandu. We found that 77.1% of the individuals carried one or more parasite taxa. This prevalence is comparable to other recent surveys of temple macaques in the Kathmandu Valley, where infection rates were reported as high as 87.6% (Adhikari et al. 2023). Taken together, these independent studies indicate that high parasite prevalence is a stable and widespread feature of macaque populations associated with heavily urbanized religious sites. In contrast, macaques inhabiting less disturbed rural habitats in Nepal, such as the Daunne Forest, exhibit a substantially lower prevalence of 39.2% (Tandan et al. 2023), highlighting a clear difference linked to landscape context.

This urban–rural contrast lends strong support to the ‘urban burden hypothesis.’ Urban environments impose a suite of ecological and behavioural changes that both increase exposure and weaken host resistance (Neiderud 2015; Theodorou 2022). At Pashupatinath and Swayambhunath, several characteristics converge such as high macaque density, concentrated human activity, routine provisioning by visitors, and frequent ground‐level foraging. These factors create repeated opportunities for faecal contamination of shared surfaces, food items, and water. This combination of factors means that macaques and humans are constantly exposed to infective stages, leading to a high risk of transmission (Kuasit et al. 2025; Schurer et al. 2019).

The parasite assemblage we detected reflects these selective pressures. Protozoa (Entamoeba sp., Giardia sp.) and direct‐transmission nematodes (Strongyle‐type eggs, Strongyloides sp.) were predominantly found. Each of these taxa relies primarily on faecal–oral transmission or direct skin penetration, and all have relatively simple life cycles. The ‘urban filter’ hypothesis posits that urbanized ecosystems favour generalist parasites with direct transmission cycles. Conversely, specialist parasites requiring complex life cycles are suppressed because their intermediate hosts (like aquatic snails or certain insects) are less abundant and ecological networks are disrupted (Werner and Nunn 2020). The low prevalence of Taenia sp. (5.7%), a cestode that relies on an intermediate vertebrate host, provides strong support for this concept.

4.1. Public Health Implications and Zoonotic Risk

The genera we identified include species with well‐documented zoonotic potential, of which Entamoeba (37.1%) and Giardia (13.3%) are of particular public health concern (Patouillat et al. 2024). Although microscopy limits identification to the genus level and cannot distinguish pathogenic E. histolytica from its nonpathogenic look‐alikes, the mere presence of these genera in a dense macaque population that interacts daily with humans signals a tangible risk.

Soil‐transmitted helminths add another layer of concern. Strongyloides sp. (20.0%) and Strongyle‐type eggs (25.7%) imply substantial environmental contamination and the possibility of percutaneous infection (Ndao et al. 2022; Winslow et al. 2024). In the religious practices observed at our study sites where barefoot walking and sitting on temple grounds are common, people frequently come into direct contact with soil and surfaces that may harbour infective stages. The detection of Ascaris and Trichuris in macaques further corroborates widespread faecal contamination of the environment. High parasite prevalence in macaques, coupled with the presence of potentially zoonotic genera, the practice of visitor feeding, and a steady influx of tourists, creates a significant and ongoing exposure hazard (Patouillat et al. 2024). Additionally, the sites function as ongoing points of contact between wildlife and a broad human population that includes individuals with varied immunity and different hygienic practices. That heterogeneity increases the likelihood of cross‐species exposure and local spillover events (Shano et al. 2021).

4.2. Consequences for Macaque Health and Transmission Dynamics

High infection burdens also matter for macaque welfare and population dynamics. Over 63% of the infected individuals harboured multiple parasite genera, a pattern consistent with chronic, multi‐pathogen exposure. Heavy, concurrent parasitism in primates is associated with malnutrition, anaemia, immune suppression, reduced reproductive success, and increased vulnerability to secondary infections (Mabbott 2018; Marcogliese and Pietrock 2011). These effects can lower individual fitness and, if widespread, reduce population resilience.

A further concern is the feedback loop between host health and environmental contamination. Animals weakened by heavy parasitism often shed more eggs and cysts, which increases the contamination of shared spaces and heightens transmission risk for both macaques and humans. In other words, poor health driven by anthropogenic conditions amplifies, rather than mitigates, infection pressure (Davenport et al. 2024).

4.3. Management Implications and the One Health Response

The epidemiological situation at these temple sites poses a difficult management dilemma. Culling or indiscriminate removal would be ethically fraught and unlikely to solve the underlying drivers. Instead, pragmatic, culturally sensitive, and evidence‐based interventions are required. Intervention strategies should begin with environmental management, including regulated feeding programs managed by local authorities (such as the Pashupati Area Development Trust and Swayambhu Management Committee). Establishing designated, elevated feeding platforms would discourage ground‐level foraging, directly breaking the soil‐faecal transmission cycle for robust environmental parasites such as Strongyloides (Garn et al. 2022).

Furthermore, direct health and behavioural measures are necessary. While periodic health screenings with targeted anthelmintic treatments for commensal macaques could reduce the overall parasite burden, we must acknowledge the severe logistical challenges of bait‐dosing wild populations and the inherent risks of promoting anthelmintic drug resistance. Therefore, these measures must be carefully weighed and monitored. All measures should be implemented within an operationalized One Health framework that coordinates veterinary, public health, and environmental authorities. Crucially, this must include human health surveillance and protection. We recommend implementing occupational health monitoring for high‐risk temple sweepers and staff, alongside the installation of accessible handwashing stations and hygiene education campaigns to reduce risky behaviours among regular visitors.

4.4. Limitations and Future Directions

It is important to acknowledge certain methodological considerations in this study. Our reliance on conventional microscopy, while effective for a general survey, has inherent limits in taxonomic resolution. For instance, this technique cannot differentiate between the pathogenic E. histolytica and the non‐pathogenic Entamoeba dispar, nor can it precisely speciate many Strongyle‐type eggs. Furthermore, the cross‐sectional design of our sampling provides a valuable snapshot over a 2‐month period but does not capture the seasonal fluctuations in prevalence that other studies have documented.

Additionally, because our sampling strategy was strictly non‐invasive and opportunistic, we were unable to capture host‐specific demographic and behavioural variables, such as exact age, sex, troop hierarchy, or individual ranging patterns. The absence of these variables, alongside a lack of quantitative environmental sampling (e.g., soil and water testing), constrained our ability to perform multivariate risk‐factor statistical analyses.

Future work building on these findings would benefit from incorporating molecular diagnostics such as polymerase chain reaction and sequencing. Such methods would enhance taxonomic precision by confirming the presence of pathogenic Entamoeba species, identifying zoonotic Giardia assemblages, and speciating helminths, particularly Strongyle‐type nematodes (Berrilli et al. 2011). A longitudinal surveillance study conducted over at least one full year would also be invaluable for clarifying seasonal dynamics, which would better inform the timing of potential interventions. Ultimately, combining parasitological data with behavioural observations and environmental sampling of soil, water, and fomites would offer a more holistic understanding and help identify the most effective points for reducing transmission.

5. Conclusion

This study demonstrates a high prevalence and diversity of GI parasites, many with zoonotic potential, in rhesus macaques at Pashupatinath Temple and Swayambhunath Stupa. The predominance of directly transmitted parasites and the heavy infection burden highlight how these urban religious sites act as amplifiers of environmental contamination.

While morphological diagnostics cannot definitively confirm active cross‐species transmission, the results confirm a substantial and ongoing shared exposure risk at the human–macaque interface, with implications for wildlife health and conservation as well. Addressing this challenge requires a coordinated, operationalized One Health approach that combines improved sanitation, elevated feeding platforms, public awareness, human health surveillance, and sustained health monitoring of macaque populations. Ultimately, this study provides a crucial, updated epidemiological baseline that justifies and guides future, highly targeted molecular surveillance at these UNESCO heritage sites.

Author Contributions

Yashoda Khadka: conceptualization, data curation, investigation, writing – original draft, writing – review and editing. Ananta Dahala: conceptualization, methodology, resources, supervision, writing – review and editing. Sujan Adhikari: methodology, software, validation, formal analysis, visualization, writing – original draft, writing – review and editing. Akash Adhikari: software, formal analysis, project administration, writing – review and editing. Aarati Sigdel: data curation, investigation, writing – review and editing. Chet Raj Pathak: conceptualization, methodology, validation, formal analysis, resources, supervision, project administration, writing – review and editing.

Funding

The authors have nothing to report.

Ethics Statement

This study was conducted using non‐invasive methods, collecting only freshly voided faecal samples without any direct handling, trapping, or disturbance of the macaques. All procedures adhered to the ethical guidelines for observational research as set by the Agriculture and Forestry University. All collected faecal samples were safely disposed of as biomedical waste after laboratory analysis.

Conflicts of Interest

The authors declare no conflicts of interest.

Contributor Information

Yashoda Khadka, Email: yashodakhadka695@gmail.com.

Ananta Dahal, Email: adahal@afu.edu.np.

Aarati Sigdel, Email: aarati.sigdel@favf.edu.np.

Chet Raj Pathak, Email: crpathak@afu.edu.np.

Data Availability Statement

The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Data Availability Statement

The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.

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