Zoonotic Giardia Strains Found in Bangkok Temple Cats, Study Shows

Stray cats living at Buddhist temples across Bangkok are carrying Giardia duodenalis, a microscopic intestinal parasite that infects an estimated 200 million people worldwide, and some of the strains they harbor are the same genetic types found in humans, according to a new molecular study published in Frontiers in Parasitology. The research, led by scientists at Kasetsart University in Thailand, provides the first molecular epidemiological picture of giardiasis in temple stray cats, a population that lives in close, daily contact with monks, caretakers, and visitors in one of Southeast Asia’s largest cities.

The cross-sectional study, conducted between June and December 2015, covered an ambitious sampling frame: 500 stray cats residing across 43 temples in 24 districts of Bangkok. Temple cats in Thailand include both semi-domesticated animals that tolerate human feeding and handling and strictly feral individuals that avoid people and rely on scavenging. Because these animals congregate in public spaces where they defecate in shared soil and sand areas, they represent a potentially important interface between animal reservoirs and human communities, yet molecular data on this population had been almost entirely absent from the literature.

Detection relied on a nested polymerase chain reaction assay targeting the small subunit ribosomal RNA (SSU rRNA) gene, a multi-copy locus chosen for its high sensitivity in confirming the presence of parasite DNA. Genomic DNA was extracted from roughly 200 milligrams of each fecal sample using a commercial stool DNA kit, with concentration and purity verified by spectrophotometry before storage at minus 20 degrees Celsius. Positive samples were then subjected to genotyping at two single-copy, highly discriminatory loci: the glutamate dehydrogenase (gdh) gene and the triosephosphate isomerase (tpi) gene, which together allow assignment of isolates to specific genetic assemblages and sub-assemblages.

The results showed an overall prevalence of 10.8 percent, with 54 of the 500 cats testing positive and a 95 percent confidence interval of 8.4 to 13.8 percent. Infection was not confined to a few hotspots: positive cases appeared in 12 of the 24 surveyed districts, half of the districts sampled, and in 19 of the 43 temples, nearly 44 percent of the sampled sites. District-level prevalence ranged widely, from 30.0 percent in Bang Sue and 27.6 percent in Khlong Sam Wa down to under 5 percent in Don Mueang and Phasi Charoen, and zero detections in twelve districts where no positive animals were found.

Genotyping succeeded for only eight of the 54 positive samples, a limitation the authors attribute to the well-known difficulty of amplifying single-copy genes directly from fecal material, likely compounded by prolonged DNA storage. Among these eight isolates, assemblage B, specifically sub-assemblage BIV, was the most common, identified in four isolates. Assemblage F, the feline-adapted type, was found in three isolates, and assemblage A, sub-assemblage AI, appeared in a single isolate. Sequences showed 99 to 100 percent identity with reference strains in GenBank, and Maximum Likelihood phylogenetic trees built on the Tamura 3-parameter model clustered the new sequences with their respective reference groups, confirming the assignments.

The assemblage findings carry real public health weight. Assemblages A and B are the only two of the eight known G. duodenalis assemblages, labeled A through H, that are considered zoonotic, meaning they infect humans as well as a broad range of mammals. Sub-assemblage AI is regarded as zoonotic, and BIV is commonly found in human infections worldwide. The feline-adapted assemblage F, meanwhile, has occasionally been reported in human cases in Thailand, adding another layer of concern. All three types detected in the temple cats have previously been documented in Thai humans, domestic animals, and wildlife, suggesting overlapping transmission cycles in these communities.

When the team explored factors associated with PCR positivity using multivariable logistic regression, one result stood out: cats with no human contact had nearly nine times higher odds of testing positive than cats that tolerated people, with an adjusted odds ratio of 8.80 and a confidence interval of 2.15 to 35.98. The authors caution that this association is exploratory, based on a small and highly imbalanced subgroup of only 15 feral cats, and the wide confidence interval demands careful interpretation. Still, the biological logic is plausible. Feral temple cats may scavenge and hunt wild prey such as rodents, which are known hosts of assemblages A, B, and F, and reptiles, which have recently been identified as carriers of zoonotic assemblage B in Thailand. Contaminated water and soil could also serve as environmental reservoirs of the hardy infective cysts.

Conversely, cats that accept human contact may benefit from a form of informal caregiving. Temple cats that tolerate people are often fed by monks and local residents, potentially receiving better nutrition and cleaner water, which could reduce their need to hunt and scavenge and thereby lower their exposure to contaminated environments. Nutrition itself may matter: inadequate protein intake has been linked in prior research to increased susceptibility to giardiasis. Because the study did not directly measure scavenging behavior, diet quality, or environmental contamination, these explanations remain untested hypotheses that the authors say require further investigation.

Notably, several conventional risk factors showed no significant association with infection. Age, sex, geographic zone within Bangkok, and deworming history all failed to predict PCR positivity in the final model. The authors suggest that the free-roaming lifestyle of stray cats exposes them so uniformly to contaminated environments that demographic differences wash out, a pattern consistent with much of the international literature, though studies elsewhere have reported conflicting results for both age and sex. The lack of a deworming effect may reflect the broad timeframe over which treatments were recorded and uncertainty about which specific anthelmintic drugs were actually administered.

The study has limitations that temper its conclusions. Convenience sampling within temples means the findings apply to the sampled animals rather than to Bangkok’s entire stray cat population, and a single cross-sectional sampling may have underestimated true prevalence because infected cats shed cysts intermittently. Sparse data prevented cluster-adjusted statistical models from converging, so temple-level clustering could not be controlled. The low genotyping success rate also means mixed assemblage infections, though not detected, cannot be ruled out. Despite these constraints, the researchers emphasize that this is the first molecular epidemiological study of G. duodenalis in temple stray cats in Thailand, and they call for future work incorporating paired sampling across human, animal, and environmental interfaces under a One Health framework to determine whether these cats actively contribute to zoonotic transmission or merely reflect the parasites circulating in their surroundings.

Subject of Research: Molecular prevalence and genetic assemblage characterization of Giardia duodenalis in temple stray cats in Bangkok, Thailand

Article Title: Molecular detection and genetic characterization of Giardia duodenalis in temple stray cats in Bangkok, Thailand

Article References: Le, V. T. T., Phoosangwalthong, P., Hoang, M.-T. T., & Inpankaew, T. (2026). Molecular detection and genetic characterization of Giardia duodenalis in temple stray cats in Bangkok, Thailand. Frontiers in Parasitology, 5, Article 1948035. https://doi.org/10.3389/fpara.2026.1948035

Image Credits: AI Generated

DOI: 10.3389/fpara.2026.1948035

Keywords: Giardia duodenalis, stray cats, Bangkok, Thailand, zoonotic parasites, molecular epidemiology, assemblage B, assemblage F, nested PCR, gdh gene, tpi gene, public health