B chromosomes (Bs) are supernumerary to the standard chromosome set, from which they prevalently derive. Variation in numbers both among individuals or populations and among cells within individuals is their constant feature. Leisler’s bat Nyctalus leisleri (Kuhl, 1817) is one of only four species of Chiroptera with detected Bs. Four males of N. leisleri were collected from two localities on the territory of Serbia and cytogenetically analysed. All animals had Bs with interindividual variability ranging from two to five heterochromatic micro Bs. The highest number of Bs was detected in this species. Among mammals, Rodentia and Chiroptera are orders with the largest number of species, but Bs frequently appear in rodents and rarely in chiropterans. Possible explanations for this difference are offered.

Wild carnivores can maintain ectoparasites and vector-borne pathogens at wildlife–domestic animal–human interfaces. We characterized ectoparasites and selected vector-associated agents in golden jackals (Canis aureus), red foxes (Vulpes vulpes), Eurasian badgers (Meles meles) and European wildcats (Felis silvestris) sampled in three regions of Serbia from October 2022 to January 2023. Of 122 animals examined, 77 carried ectoparasites; 68 ticks and 254 fleas were collected. Ticks comprised Ixodes ricinus (n = 37, from which n = 23 on C. aureus, n = 14 on V. vulpes), Dermacentor reticulatus (n = 23, from which n = 12 on C. aureus, n = 11 on V. vulpes), Rhipicephalus spp. (n = 3, from which n = 2 on C. aureus, n = 1 on V.vulpes), and Haemaphysalis punctata (n= 5, from which n = 2 on C. aureus, n = 3 on V.vulpes), whereas fleas comprised Ctenocephalides canis (n = 171, from which n = 97 on C. aureus, n = 64 on V. vulpes, n = 9 on Meles meles, n = 1 on Felis silvestris), C. felis (n = 36, from which n = 14 on C. aureus, n = 12 on V. vulpes, n = 10 on Meles meles), Pulex irritans (n = 25, from which n = 15 on C. aureus, n = 6 on V. vulpes, n = 4 on Meles meles), Ceratophyllus gallinae (n = 21, from which n = 5 on C. aureus, n = 16 on V. vulpes) and Xenopsylla cheopis (n = 1 on C. aureus). Molecular screening detected Hepatozoon canis DNA in six tick samples, Babesia spp. DNA in three tick preparations and Bartonella spp. DNA in 13 flea samples; the remaining bacterial, protozoal and viral targets were not detected. Sanger sequencing yielded sequences assigned to Babesia canis (n = 2), H. canis (n = 4) and Bartonella rochalimae (n = 13). Phylogenetic analyses placed the study sequences with related Eurasian reference lineages. These findings document a diverse ectoparasite fauna and vector-associated pathogen circulation in Serbian wild carnivores and support continued One Health surveillance using paired host-vector sampling.