This study demonstrated a moderate prevalence of gastrointestinal parasites among both avian and mammalian species in a zoo in Ankara, with parasite community structure varying substantially according to host class and species. The overall prevalence observed was lower than the 68.3% reported in the Rio de Janeiro Zoo
11 and the 42.3% reported in a Chinese zoo
1, yet it remains consistent with the range frequently reported in captive populations. Such variability across institutions is commonly attributed to differences in management practices, housing conditions, diet, and prophylactic protocols
2.
In this study, prevalence was higher in birds than in mammals, a finding that partly contrasts with the ten-year monitoring of two institutions in Spain, where Esteban-Sánchez et al.2 reported higher prevalence among mammals. However, that study included mammalian sample sizes 4.5 times greater than avian samples, which may explain the divergence. Local husbandry factors such as flooring type, moisture, food and water hygiene, prophylactic regimens, and stocking density likely account for such discrepancies. Indeed, the literature emphasizes that environmental and management-related factors often exert a stronger influence than host class when comparing institutions2,12. Logistic regression in our dataset indicated a higher risk of infection in males, a finding consistent with observations in other captive animal studies where sex-related differences in behavior and social stress potentially influence exposure risk13.
From a taxonomic perspective, the dominance of Eimeria spp. aligns with patterns frequently observed in captive avian systems as well as broader poultry husbandry contexts1. Eimeria oocysts can remain viable for months or even years in moist environments. Thanks to their multi-layered cyst walls, Eimeria oocysts are resistant to many disinfectants. This contributes to an increase in Eimeria load in bird enclosures14,15. This finding underscores the necessity of integrating environmental interventions (e.g., litter drying, bedding management) with pharmacological control strategies. Furthermore, it highlights the importance of considering parasite communities collectively, rather than focusing on single taxa in control programs.
The co-infection analysis revealed frequent co-occurrence of Eimeria spp. with Capillaria spp. and strongylid-type eggs, whereas associations with Nematodirus and Trichuris were less common. However, it must be emphasized that co-infection heatmaps are correlation-based and do not establish mechanistic interactions. As highlighted in parasite community ecology, co-occurrence alone cannot be interpreted as causality without support from mechanistic modeling or longitudinal sampling16. Future work should validate these clusters through repeated sampling and multi-level joint species modeling approaches.
Diversity analysis indicated Shannon index values ranging from ~1.0–1.08 and Simpson (1–D) indices suggestive of moderate diversity. These values were higher than those reported in plains bison populations, where individual-level Shannon diversity was ~0.45 and herd-level ~0.75 using nemabiome methods17. They were also comparable to values typically reported for fish parasite communities, where Shannon indices are often ≤118. Collectively, these comparisons suggest that zoo populations host parasite communities characterized by balanced presence of a few dominant taxa, rather than high richness.
Species-level patterns of high prevalence were consistent with prior reports. Husbandry-related factors such as ground-level feeding, open water sources, heavy bedding use, and group housing conditions, despite frequent disinfection, can facilitate accumulation of oocysts and thus increase risk14,19. In addition, host factors such as diet and age have been associated with increased positivity in avian species, supporting the rationale for risk-based surveillance and prophylaxis tailored at class- or order-specific levels19.
The increased negativity rate (83.5%) observed among treated animals compared to untreated counterparts highlights the clinical utility of macrocyclic lactones in zoo settings, particularly against gastrointestinal nematodes. Macrocyclic lactones such as ivermectin, moxidectin, and selamectin act on glutamate-gated chloride channels and are recognized as broad-spectrum endectocides effective against nematodes. Differences in potency and resistance patterns among compounds within this class have been documented20,21. The low residual prevalence of strongylid-type eggs, Capillaria spp., Ascaridia spp., and Nematodirus spp. observed in ivermectin-treated animals is consistent with this pharmacological spectrum. Likewise, the praziquantel + imidacloprid + moxidectin regimen (used in cats) nearly eliminated nematodes, in agreement with documented endo-/ectoparasitic efficacy of topical imidacloprid 10% + moxidectin 2.5% formulations21,22. The persistence of Eimeria spp. under this regimen was expected, as praziquantel targets cestodes and trematodes, while macrocyclic lactones are ineffective against coccidia23.
The continued detection of Eimeria spp. despite routine deworming confirms that anthelmintic regimens are ineffective against coccidiosis and emphasizes the need for anticoccidial interventions. Given the resilience of Eimeria oocysts, effective control requires integrated pharmacological and environmental strategies24;25. Triazine derivatives such as toltrazuril have been shown to significantly reduce lesion scores and oocyst shedding, and when appropriately timed, can prevent recurrence26,27. Thus, rational zoo parasite control protocols should combine macrocyclic lactones for nematodes with species-appropriate anticoccidials and robust litter/moisture management.
Overall, the treatment program provided clear clinical benefit against nematodes but failed to suppress Eimeria burden due to both pharmacological limitations and environmental persistence. Integrated strategies combining species-targeted anticoccidials, litter/moisture control, and improved hygiene represent the most sustainable approach for long-term control and welfare improvement in zoo settings24-26.
From a public health perspective, this study draws attention to the potential risk of zoonotic protozoa such as Giardia. Several zoos have reported zoonotic G. duodenalis assemblages (A/B) in mammals and birds, and molecular typing has been recommended to support source attribution. Because microscopy may lack sensitivity during low-shedding phases, periodic molecular surveillance of high-risk species would be advisable2,28.
Methodologically, the flotation and sedimentation approaches employed here are practical routine techniques for zoo surveillance. However, sensitivity may be limited for some taxa beyond trematodes, and intermittent egg/oocyst shedding may yield false negatives in single samples. The literature suggests that advanced quantitative methods such as Mini-FLOTAC/FLOTAC and serial sampling improve detection performance7;8;19. The use of Wilson’s method for prevalence confidence intervals in this study is also advantageous, as it provides more reliable coverage for small sample sizes, thus increasing the robustness of our estimates10.
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