Endoparasites in carnivores in Swiss zoological institutions between 2009 and 2024: evaluation of risk factors and deworming strategies

Parasitic infections in zoo carnivores pose risks to animal health and zoonotic transmission. Over a 15-year period, endoparasites were detected in faecal samples from Swiss zoo carnivores, with clinical and management data used to identify factors linked to parasite occurrence. The samples, originating from 50 species kept in 30 different institutions, were collected in 2009 (n = 140), 2018 (n = 149) and 2024 (n = 116), and analysed by Baermann-Wetzel technique, combined sedimentation/flotation, <i>Giardia</i> coproantigen detection and Ziehl-Neelsen staining of faecal smears. Fifteen samples were further analysed by biomolecular methods. Odds ratios and 95 % confidence intervals (OR, 95 % CI) were calculated to compare management strategies and assess potential risk factors. Overall, 198/405 (48.9 %) of the samples tested positive. The most frequent parasites were ascarids (n = 73), followed by <i>Capillaria</i> spp. (n = 66), <i>Cystoisospora</i> spp. (n = 50) and <i>Cryptosporidium</i> (n = 43). Most animals were asymptomatic. Among the animals with clinical observations available, diarrhoea was recorded in ten, respiratory signs in two and reduced body condition in four individuals. Of these, intestinal (e.g., ascarids, hookworms, <i>Cystoisospora</i> sp., <i>Cryptosporidium</i> sp.) or respiratory (e.g., <i>Angiostrongylus vasorum</i>, <i>Capillaria boehmi</i>) parasites were identified in seven animals. Hunting mice, birds, rodents or eating snails was significantly associated with positive findings (OR: 2.3, 95 % CI: 1.0-5.0, p = 0.04), whereas on-site slaughter of food animals appeared protective (OR: 0.5, 0.2-1.1, p = 0.09). Zoonotic parasites such as <i>Strongyloides</i> sp. (n = 3) and <i>Baylisascaris</i> sp. (n = 3) were rarely detected. Animals from institutions that did not apply any parasitological management measures (deworming and/or faecal examinations) were more likely to be positive for helminths compared to those from zoos applying such measures (OR: 3.4, 95 % CI: 1.1-10.3, p = 0.03). Although often subclinical, some parasites-especially respiratory helminths-can affect animal health, and stress or anaesthesia may exacerbate diseases in valuable individuals. Targeted, diagnosis-based deworming reduces anthelmintic use, and consequently the risk of resistance and the likelihood of adverse effects.