Hidden Parasites Surface in Brazilian Zoo Animals in Landmark Survey

Deep inside one of Brazil’s oldest zoological parks, an invisible census has just been completed. Researchers examining fecal samples from hundreds of animals at the Getúlio Vargas Zoobotanical Park in Salvador, Bahia, found that more than half of the samples tested positive for internal parasites, and several of the parasite–host pairings they documented had never been recorded before anywhere in the scientific literature. The findings, published in Frontiers in Parasitology, offer one of the most detailed snapshots to date of the hidden parasitic fauna circulating among mammals, birds, and reptiles under human care in northeastern Brazil, and they carry implications that reach far beyond the park’s gates, touching on animal welfare, conservation breeding programs, and even occupational health for zoo staff.

The study targeted the Getúlio Vargas Zoobotanical Park, a 25-hectare green space in the heart of Salvador that preserves remnants of secondary Atlantic Forest under a tropical, hot and humid climate, with roughly 1,800 millimeters of annual rainfall and mean temperatures around 25 degrees Celsius. That setting matters: Brazil harbors approximately 20 percent of the world’s biodiversity across its six major biomes, and zoos like this one hold a substantial share of threatened species in their collections. In total, the survey covered 75 species and 409 individual animals, including 40 mammal species with 229 individuals, 27 bird species with 153 individuals, and seven reptile species with 27 individuals, ranging from jaguars and maned wolves to harpy eagles, scarlet ibises, and Burmese pythons.

Because sampling relied on fecal material rather than invasive procedures, the team collected pooled samples directly from enclosure floors during routine cleaning periods in December 2021, taking care to gather only the inner portions of each fecal mass to avoid contact with soil and reduce the risk of environmental contamination. Samples were preserved in 5 percent formalin and shipped to the Animal Parasitology Laboratory at the Federal Rural University of the Semi-Arid Region for analysis. Not every animal could be sampled; some reptiles, particularly those that defecate infrequently or spend extended periods in water, such as freshwater turtles and caimans, did not produce usable material during the collection window. The researchers therefore treated the enclosure, not the individual animal, as their sampling unit, a conservative choice that shapes how the results should be read.

The methodological heart of the study lies in its decision to run four complementary coproparasitological techniques in parallel on every sample: the direct method, spontaneous sedimentation, Willis flotation in hypersaturated sodium chloride, and the Mini-FLOTAC system, a modern flotation device that also allows quantification of eggs, oocysts, and larvae per gram of feces. The choice was deliberate, because each technique excels at recovering different parasitic structures. Flotation methods preferentially float light eggs and oocysts in dense solutions, sedimentation is better suited to heavier eggs such as those of trematodes that resist flotation, and the direct method, though less sensitive in low-intensity infections, provides rapid detection of larvae, protozoan stages, and eggs in fresh material. Each slide for the first three techniques was read independently by two evaluators to increase reliability.

The headline number is stark: 52.8 percent of the 144 samples analyzed were positive for endoparasites. Among the positive samples, nematodes dominated at 80.3 percent, followed by protozoa at 23.7 percent, cestodes at 13.2 percent, and trematodes at 10.5 percent, and just over a quarter of positive samples, 26.3 percent, harbored mixed infections involving two or more parasite groups. Descriptively, the direct method detected parasite structures in 38.2 percent of all samples, spontaneous sedimentation in 36.1 percent, Willis flotation in 32.6 percent, and Mini-FLOTAC in 26.4 percent, a spread that vividly illustrates why no single diagnostic test tells the whole story. The researchers cautioned that they used the techniques as complementary tools rather than competing benchmarks, and did not formally compare their diagnostic performance.

Broken down by host group, the results overturned a familiar pattern. Zoological surveys typically report higher parasite frequencies in birds and mammals than in reptiles, but here reptiles led with 66.7 percent positivity, followed by birds at 60.0 percent and mammals at 47.8 percent. The authors suggest this inversion may reflect the specific species sampled and the nature of parasitism in reptiles, which is often asymptomatic or oligosymptomatic and therefore easy to miss clinically. Within mammals, the parasite inventory was rich and taxonomy-specific: primates carried coccidia, Strongyloides roundworms, the tapeworm genus Bertiella, and the fluke Platynosomum; carnivores harbored Strongyloides and pinworms of the family Oxyuridae; even-toed ungulates such as deer and peccaries carried the ciliate Balantioides alongside whipworms and Strongyloides; odd-toed ungulates, including the South American tapir and plains zebra, showed strongyles and Balantioides; and opossums proved to be a hotspot, hosting Eimeria, Cruzia, Aspidodera, and an assortment of other nematodes at strikingly high egg counts.

Birds and reptiles added their own distinctive entries. Psittacines, from macaws to parakeets, tested positive for Capillaria hairworms, ascarid roundworms, and strongyles, with red-browed amazons showing ascarid loads of up to 3,700 eggs per gram. Passerines, including rufous-bellied thrushes and sayaca tanagers, carried Isospora and unsporulated coccidia, with one tanager sample reaching a remarkable 80,304 oocysts per gram. Among reptiles, snakes shed coccidia and rhabditiform larvae, the green iguana carried pinworm eggs, and the red-footed tortoise proved especially diverse, yielding Nyctotherus and Balantioides protozoa, strongyle eggs, coccidia, and larvae of the family Atractidae. Notably, several of the identified parasites, including Balantioides, Strongyloides, Trichuris, and Platynosomum, have known or suspected zoonotic potential, meaning they can pose a genuine occupational risk to keepers, veterinarians, and anyone in close contact with the animals or their enclosures.

The most consequential findings are the first-ever parasite records for specific host species. The team reports, for the first time, the occurrence of Strongyloides roundworms in the white-cheeked spider monkey and the golden-headed lion tamarin, Bertiella tapeworms in the blond titi monkey and the common squirrel monkey, and Capillaria hairworms in the red-browed amazon, the peach-fronted parakeet, and the red-shouldered macaw. Several of these hosts are themselves conservation priorities, and the blond titi monkey in particular is a critically endangered species endemic to the Caatinga. Documenting these associations expands the known host ranges of common parasite genera and gives veterinarians managing captive populations a better map of what to screen for, when to treat, and how to design quarantine and deworming protocols that protect both collection animals and staff.

Why does parasitism run so high in captivity in the first place? The authors point to a convergence of factors: limited space, elevated host density, close proximity between species, and chronic stress that can suppress immune responses, all of which favor transmission. Many of the dominant parasites, including most nematodes and protozoa, have direct life cycles requiring no intermediate host, so infective stages accumulate quickly in shared enclosures. Contact with synanthropic wildlife, free-roaming animals that thrive around human settlements, adds another transmission route that is notoriously difficult to control. Left unchecked, these infections can progress from silent subclinical states to anorexia, weight loss, gastrointestinal disease, anemia, and reduced survival and reproductive success, outcomes that directly undercut the conservation mission zoos exist to serve.

The study is candid about its limits. Feces were collected as pooled samples from enclosure floors, so results describe positivity at the enclosure or sample level rather than true individual prevalence, and the single December 2021 sampling campaign captures only a moment in time, leaving seasonal fluctuations unexplored. Formalin preservation and the absence of molecular confirmation restricted some identifications to morphological categories, and the Mini-FLOTAC dilution followed the manufacturer’s recommendation for dogs and cats, which may not be optimized for every host group examined. Even so, the authors argue that the takeaway is clear and urgent: systematic parasitological monitoring is not an optional extra for zoological institutions but a cornerstone of animal health management, and longitudinal studies with repeated seasonal sampling are the logical next step. For a park sheltering jaguars, lion tamarins, and harpy eagles in the remnants of the Atlantic Forest, knowing which parasites share the enclosures is the first line of defense for the animals, the people who care for them, and the species they may one day help return to the wild.

Subject of Research: Endoparasitic fauna in captive mammals, birds, and reptiles at a Brazilian zoobotanical park, detected through complementary coproparasitological methods

Article Title: Parasitological study of animals maintained under human care at a Zoobotanical Park in Bahia, Northeastern Brazil

Article References: Batista, A. I. V., Gurgel, J. V. D. O., Pereira, L. M. F., Ferreira, P. R. B., Gomes, M. C., Brasil, A. W. D. L., Lima, V. F. S., Coelho, W. A. C., Carvalho, L. R. R. A., & Pereira, J. S. (2026). Parasitological study of animals maintained under human care at a Zoobotanical Park in Bahia, Northeastern Brazil. Frontiers in Parasitology, 5, Article 1929185. https://doi.org/10.3389/fpara.2026.1929185

Image Credits: AI Generated

DOI: 10.3389/fpara.2026.1929185

Keywords: coproparasitology, zoo animals, endoparasites, nematodes, zoonoses, Strongyloides, Bertiella, Capillaria, conservation, Brazil, Mini-FLOTAC, captive wildlife