Sloth poop may not look like a scientific treasure, but it can reveal a hidden community living inside an animal. In Costa Rica, researchers used dung samples to investigate the gastrointestinal parasites of wild sloths without needing to disturb them for invasive tests.
Their 2025 study compared Hoffmann's two-fingered sloths and brown-throated three-fingered sloths living in primary rainforest and urban habitats. From just 38 samples, the team detected eight parasite types. The biggest surprise was not how many they found, but how completely the two sloth species differed.
This does not mean that the animals were all sick. Parasites are part of natural ecosystems, and finding them is not the same as diagnosing disease. The research instead gives conservationists and wildlife vets a much-needed baseline for understanding sloth health.
How do you study parasites in a wild sloth?
Researchers collected faecal samples between March and July 2023 on Costa Rica's Caribbean coast. Their main study areas were La Selva Biological Station, surrounded by protected lowland rainforest, and the more urban landscape around Puerto Viejo de Talamanca.
Some samples were found at the bases of trees used by sloths as latrines. Others came from the first sample produced by animals admitted to wildlife hospitals. The team preserved the material and examined it using established microscopy and parasitology methods.
This approach is called coprological analysis. It allows scientists to look for parasite eggs, cysts and other diagnostic structures in dung. It cannot answer every question or always identify a parasite to species level, but it is an especially useful first step when the animals being studied are elusive, tree-dwelling and difficult to observe.
Eight parasite types in 38 samples
The open-access PeerJ study record examined 38 samples from free-ranging sloths and detected eight gastrointestinal parasite morphotypes. A morphotype is a visually distinct form seen under the microscope. It may represent a species, but researchers need more evidence before giving an unfamiliar organism a firm name.
The eight forms matched the total number of gastrointestinal parasite types previously recorded from adult specimens in sloths across roughly a century of scientific literature. That does not mean the study discovered eight new species. It shows how little basic information has been collected and how much a focused field season can add.
The samples included signs of nematodes, cestodes and coccidia. Some of the forms could not yet be identified precisely, and the authors say further work using adult specimens, genetic methods and broader sampling will be needed.
Two sloths, two completely different communities
Hoffmann's two-fingered sloths and brown-throated three-fingered sloths can occupy the same Costa Rican landscapes. They may even use the same trees. Yet the study found no gastrointestinal parasite morphotypes shared between the two host species.
That clean split suggests host identity was more important than shared habitat in shaping these parasite communities. The two kinds of sloth look similar because they independently evolved an upside-down, energy-saving life in the canopy, but they belong to distant evolutionary lineages. Differences in anatomy, digestion, behaviour or immunity may create very different conditions for parasites.
The result is a reminder that the word "sloth" covers animals with distinct biology. Wildlife care, rescue decisions and disease monitoring cannot safely assume that a parasite associated with one sloth species will behave the same way in another.
Does a parasite mean an unhealthy forest?
Not necessarily. The study did not find a statistically significant overall effect of habitat type on parasite composition or richness. There was a marginal trend suggesting that two-fingered sloths in primary forest hosted more parasite types than those in urban areas, but the sample was small and the result needs further testing.
Parasite diversity can be part of a complex, functioning ecosystem. Some parasites cause disease, while others may have little obvious effect under normal conditions. A richer parasite community is therefore not automatically proof that animals are less healthy, just as finding fewer parasite types in a fragmented habitat is not automatically good news.
The careful conclusion is that scientists need more data. Future studies can test whether diet, intermediate hosts, contact with domestic animals, forest structure or stress changes which parasites sloths carry and whether those organisms affect health.
Why this matters for rescue and rewilding
Sloths frequently enter wildlife clinics after electrocutions, road incidents, dog attacks and other emergencies. Some later return to the wild. Better knowledge of normal parasite communities can help vets interpret test results and avoid moving harmful organisms between regions, facilities or species.
The Sloth Conservation Foundation's summary also highlights an important conservation lesson: understanding wildlife health is not only about treating obvious illness. It is about learning what is normal before a crisis appears.
Thirty-eight samples cannot map every hidden passenger in Costa Rica's sloths. They can, however, turn a neglected corner of sloth biology into testable questions. Sometimes conservation science begins with a thermal drone or a GPS collar. Sometimes it begins by looking very closely at what an animal leaves beneath a tree.
Sources and image credit
- Vanderhoeven and colleagues: Host specificity of gastrointestinal parasites in free-ranging sloths from Costa Rica
- The Sloth Conservation Foundation: Gastrointestinal Parasites in Wild Sloths
- Featured image: Jsfouche, CC BY-SA 3.0, via Wikimedia Commons. The photo shows a Hoffmann's two-toed sloth at the Jaguar Rescue Center in Costa Rica.
