Hepatozoon spp. are protozoa from the phylum Apicomplexa (Adeleorina: Hepatozoidae) which infect vertebrates and are transmitted by hematophagous arthropods including ticks, mites, fleas, lice, reduviid bugs, mosquitoes, tsetse flies and sand flies, who serve as final hosts. Different Hepatozoon spp. have been described to infect amphibians, reptiles, birds, marsupials and mammals as intermediate hosts (Smith, 1996). There are currently more than 340 species in the genus Hepatozoon, with most of them described in reptiles and amphibians (Smith, 1996, Baneth, 2011). The genus includes groups of species with a broad genetic diversity among them (Thomas et al., 2024). Both domestic and wild animals serve as hosts for Hepatozoon spp., with transmission occurring between closely related species, such as wild and domestic carnivores (Uiterwijk et al., 2023, Thomas et al., 2024, Dubey and Baneth, 2025). Some Hepatozoon spp. cause severe disease in their hosts, such as Hepatozoon americanum in domestic dogs and Hepatozoon silvestris in domestic cats, while others are mostly associated with sub-clinical infection or signs of mild disease (Dubey and Baneth, 2025).

Hepatozoon felis reported initially from a domestic cat in India in 1908 and named Leuckocytozoon felis domesticate (Patton, 1908a, Patton, 1908b) was described shortly after the description of Hepatozoon canis from a dog also in India (James 1905). The Leukocytozoon species of the dog and cat were transferred to the family Hepatozoidae about two decades after their first description (Wenyon 1926) and were thereafter placed in the genus Hepatozoon. Contrary to H. canis which was reported to be transmitted by the brown dog tick Rhipicephalus sanguineus sensu lato shortly after its discovery (Christophers, 1907, Christophers, 1912), the arthropod vector of H. felis was not elucidated up to the present time. Searches for the developmental stages of H. felis in an arthropod vector were performed in the cat flea, Ctenocepahalus felis and the tick Haemalphysalis fusca already early in the 20th century (Patton, 1908b), however, unsuccessfully. Further studies demonstrating H. felis DNA in several hematophagous arthropods including cat fleas and the ticks Rhipicephalus turanicus, Ixodes ricinus and Ixodes hexagonus, merely demonstrate that these hosts took a blood meal from an infected vertebrate host, but could not determine that these arthropods are indeed vectors of this parasite (Kamani et al., 2018, Duplan et al., 2018, Hornok et al., 2022, Önder et al., 2025).

Hepatozoon felis infection is widespread in cat populations in many areas of the world. A multicenter study of cats from countries around the Mediterranean has found that the total prevalence of H. felis infection was 14.5 % among 600 cats tested. Infection was found in 30 % of the cats tested from Greece, 23 % from Portugal, 15 % from Spain, 15 % from Israel, and 4 % from France (Carbonara et al., 2023). Moreover, H. felis was detected in 75 % of 28 cats during a neutering operation in Rio de Janeiro, Brazil (Travesa et al., 2024), 15 % of 80 cats from Cape Verde islands west of Africa (Pereira et al., 2019), 8 % of 311 cats from Turkey (Önder et al., 2025), 2.9 % of 102 cats from Luanda, Angola (Oliveira et al., 2018), and in 2.9 % of 848 cats from Iran (Sazmand et al., 2025). Although H. felis infection in domestic cats is mostly sub-clinical, some studies have reported clinical disease associated with this infection. A domestic cat from Austria with H. felis infection in which other infectious diseases were ruled out was described to have poor body condition, lethargy, anorexia, fever, painful abdomen, icterus, thrombocytopenia, and leukopenia (Basso et al., 2019). Clinical pathological findings in cats with H. felis infection detected in blood smears included anemia, and increased serum muscle enzyme activities of creatine kinase and lactate dehydrogenase (Baneth et al., 1998). Another species of Hepatozoon, H. silvestris initially reported in European wild cats (Felis silvestris) in Bosnia and Herzegovina also infects cats and can cause severe disease in affected domestic cats (Hodžić et al., 2017, Kegler et al., 2018). In addition, H. canis has been reported in domestic cats, but current reports have only detected the DNA of this pathogen in cats with no apparent clinical manifestations associated with its presence (Dubey and Baneth, 2025).

In this study we aimed to detect and assess the sporogonic stages of Hepatozoon spp. in ticks removed from cats, as well as to experimentally induce and follow activation and excystation of sporocysts and sporozoites from these ticks.