An Overview of Tick-Borne Encephalitis Epidemiology in Endemic Regions of Continental Croatia, 2017-2023.

Tick-borne encephalitis (TBE) represents an important public health problem in Europe. We analyzed the epidemiology of TBE based on data from humans, animals, and Ixodes ricinus ticks in endemic regions of continental Croatia. In the period from 2017 to 2023, cerebrospinal fluid (CSF) and serum samples of 684 patients with neuroinvasive diseases, 2240 horse serum samples, and 300 sheep serum samples were tested for TBEV. In addition, 8751 I. ricinus ticks were collected. CSF samples were tested using RT-PCR. Serological tests (serum, CSF) were performed using commercial ELISA, with confirmation of cross-reactive samples by a virus neutralization test. Eighty-four autochthonous human TBEV cases were confirmed. The majority of patients were in the age group of 40-69 years (58.3%) with a male predominance (70.2%). TBE showed a bimodal seasonality with a large peak in April-August and a small one in October-November. In addition to humans, TBEV IgG antibodies were found in 12.2% of horses and 9.7% of sheep. Seasonal tick abundance corresponds to the reported number of human infections. Continental Croatia is still an active natural focus of TBE. Continuous monitoring of infections in humans, sentinel animals, and ticks is needed for the implementation of preventive measures.

Virome of Ixodes ricinus, Dermacentor reticulatus, and Haemaphysalis concinna Ticks from Croatia.

Tick-borne diseases are a serious threat to both public and veterinary health. In this study, we used high-throughput sequencing to characterize the virome of three tick species implicated in the spread of vector-borne disease throughout Croatia. Ten viruses were identified, including seven potential novel species within the viral families Flaviviridae, Nyamiviridae, Rhabdoviridae, Peribunyaviridae, Phenuiviridae, and Nairoviridae.

DNA barcoding of hard ticks (Ixodidae), notes on distribution of vector species and new faunal record for Croatia.

Molecular methods are increasingly being utilized for accurate identification of ticks (Acari: Ixodidae), especially in cases of morphologically highly similar species. In this study, we performed molecular research of the tick fauna in Croatia using DNA barcoding method. Ticks were sampled in three biogeographical regions and thirteen species were recorded: Dermacentor marginatus, Dermacentor reticulatus, Haemaphysalis concinna, Haemaphysalis inermis, Haemaphysalis punctata, Hyalomma marginatum, Ixodes frontalis, Ixodes hexagonus, Ixodes kaiseri, Ixodes ricinus, Rhipicephalus bursa, Rhipicephalus sanguineus s.l. and Rhipicephalus turanicus. Ixodes kaiseri is for the first time recorded in the fauna of Croatia. Of the thirteen hard tick species analyzed in this study, pathogens from different groups (bacteria, protozoa and viruses) have been detected in eight species in Croatia so far. For the important vector species R. sanguineus s.s., new distributional data for Croatia are given. The standard COI barcoding region was amplified, and the sequences were analyzed by species delimitation methods together with the sequences of conspecific and congeneric species from the public BOLD database. Our specimens of H. punctata represent a new, genetically distinct MOTU. A brief overview of the available public DNA barcoding data for Ixodidae is presented, highlighting the need for an integrative approach for the clarification of the taxonomic status of problematic Ixodid taxa. The results provide a basis for the establishment of a molecular data platform for the Ixodidae of the Croatian fauna.

Emerging and Neglected Viruses of Zoonotic Importance in Croatia.

Several arboviruses have emerged in Croatia in recent years. Tick-borne encephalitis is endemic in continental counties; however, new natural micro-foci have been detected. Two autochthonous dengue cases were reported in 2010. West Nile virus emerged in 2012, followed by emergence of Usutu virus in 2013. Although high seroprevalence rates of Toscana virus have been detected among residents of Croatian littoral, the virus remains neglected, with only a few clinical cases of neuroinvasive infections reported. Lymphocytic choriomeningitis virus is a neglected neuroinvasive rodent-borne virus. So far, there are no reports on human clinical cases; however, the seroprevalence studies indicate the virus presence in the Croatian mainland. Puumala and Dobrava hantaviruses are widely distributing rodent-borne viruses with sporadic and epidemic occurrence. Hepatitis E virus is an emerging food-borne virus in Croatia. After the emergence in 2012, cases were regularly recorded. Seropositivity varies greatly by region and population group. Rotaviruses represent a significant healthcare burden since rotavirus vaccination is not included in the Croatian national immunization program. Additionally, rotaviruses are widely distributed in the Croatian ecosystem. A novel coronavirus, SARS-CoV-2, emerged in February 2020 and spread rapidly throughout the country. This review focuses on emerging and neglected viruses of zoonotic importance detected in Croatia.