Detection of Tahyna Orthobunyavirus-Neutralizing Antibodies in Patients with Neuroinvasive Disease in Croatia

Current Status of Vector-Borne Diseases in Croatia: Challenges and Future Prospects

Different vector-borne pathogens are present or have (re-)emerged in Croatia. Flaviviruses tick-borne encephalitis (TBEV), West Nile (WNV), and Usutu (USUV) are widely distributed in continental regions, while Toscana virus (TOSV) and sandfly fever viruses are detected at the Croatian littoral. Recently, sporadic clinical cases of Tahyna orthobunyavirus (TAHV) and Bhanja bandavirus infection and seropositive individuals have been reported in continental Croatia. Acute infections and serologic evidence of WNV, TBEV, USUV, and TAHV were also confirmed in sentinel animals and vectors. Autochthonous dengue was reported in 2010 at the Croatian littoral. Lyme borreliosis is the most widely distributed vector-borne bacterial infection. The incidence is very high in northwestern and eastern regions, which correlates with numerous records of Ixodes ricinus ticks. Acute human Anaplasma phagocytophilum infections are reported sporadically, but there are many records of serologic evidence of anaplasmosis in animals. Mediterranean spotted fever (Rickettsia conorii) and murine typhus (Rickettsia typhi) are the main rickettsial infections in Croatia. Human leishmaniasis is notified sporadically, while serologic evidence of leishmaniasis was found in 11.4% of the Croatian population. After the official eradication of malaria in 1964, only imported cases were reported in Croatia. Since vector-borne diseases show a growing trend, continuous monitoring of vectors is required to protect the population from these infections.

Ťahyňa virus-A widespread, but neglected mosquito-borne virus in Europe

Ťahyňa virus (TAHV) is an orthobunyavirus and was the first arbovirus isolated from mosquitoes in Europe and is associated with floodplain areas as a characteristic biotope, hares as reservoir hosts and the mammal-feeding mosquitoes Aedes vexans as the main vector. The disease caused by TAHV ("Valtice fever") was detected in people with acute flu-like illness in the 1960s, and later the medical significance of TAHV became the subject of many studies. Although TAHV infections are widespread, the prevalence and number of actual cases, clinical manifestations in humans and animals and the ecology of transmission by mosquitoes and their vertebrate hosts are rarely reported. Despite its association with meningitis in humans, TAHV is a neglected human pathogen with unknown public health importance in Central Europe, and a potential emerging disease threat elsewhere in Europe due to extreme summer flooding events.

Surveillance of Tahyna Orthobunyavirus in Urban Areas in Croatia—The “One Health” Approach

Background: Tahyna orthobunyavirus (TAHV) is a neglected mosquito-borne bunyavirus. Although the virus is widespread in continental Europe, TAHV infections are rarely reported. We analyzed the prevalence of TAHV in humans and different animal species as well as mosquitoes collected in urban areas of Zagreb and its surroundings in the period from 2020 to 2022. Methods: The study included 36 patients with neuroinvasive disease (NID), 218 asymptomatic individuals, 98 horses, 94 pet animals (dogs and cats), and 4456 Aedes vexans mosquitoes. Cerebrospinal fluid (CSF) and urine samples of patients with NID were tested for the TAHV RNA using a real-time reverse transcription-polymerase chain reaction (RT-qPCR). Human and animal serum samples were tested for TAHV-neutralizing (NT) antibodies using a virus-neutralization test (VNT). Mosquito pools were tested for TAHV RNA using an RT-qPCR. Results: TAHV NT antibodies were detected in 3/9.4% of patients with NID, 8/3.7% of asymptomatic individuals, 29/29.6% of horses, and 11/11.7% of pet animals. There was no difference in the seroprevalence according to age, sex, and area of residence in asymptomatic individuals. In addition, TAHV seropositivity did not differ according to age and sex in pet animals. None of the tested mosquito pools was TAHV RNA-positive. Conclusions: The presented results highlight the importance of interdisciplinary surveillance (“One Health”) of this neglected viral zoonosis.