# First Serological Evidence of Crimean-Congo Hemorrhagic Fever Virus Infections in Croatia: A Multispecies Surveillance Approach Emphasising the Role of Sentinel Hosts

## TL;DR

This study found evidence of Crimean-Congo hemorrhagic fever virus in Croatia, mainly in sheep, highlighting the need for targeted surveillance in high-risk areas.

## Contribution

The first serological evidence of CCHFV in Croatia using a multispecies surveillance approach.

## Key findings

- 109 out of 1473 animal serum samples tested positive for CCHFV antibodies, with the highest rate in sheep.
- Seropositive animals were mainly from coastal and subcoastal regions where Hyalomma ticks are present.
- No CCHFV RNA was detected, indicating transient viremia and silent virus circulation.

## Abstract

Crimean-Congo hemorrhagic fever virus (CCHFV) is a tick-borne zoonotic pathogen of growing public health concern in southeastern Europe. This study provides the first serological evidence of CCHFV circulation in Croatia, based on testing 1473 serum samples from farm and companion animals, including sheep, horses, cattle, goats, dogs, and cats. A total of 109 samples (7.4%) tested positive for CCHFV antibodies using a commercially available enzyme-linked immunosorbent assay (ELISA) kit. The highest seroprevalence was recorded in sheep (28.3%), followed by horses (4.3%) and a single cat (0.5%), with no antibodies detected in cattle, goats, or dogs. Almost all seropositive animals originated from coastal and subcoastal Croatia, where Hyalomma ticks are present. Only two seropositive cases were detected in continental areas. Sheep samples from several farms in Zadar County showed intra-farm seropositivity rates of up to 85.7%, suggesting localised virus circulation likely influenced by vector distribution and farm-level practices. No viral ribonucleic acid (RNA) was detected by quantitative reverse transcription polymerase chain reaction (qRT-PCR), consistent with the transient nature of viremia in most animal hosts. These findings confirm the silent circulation of CCHFV in Croatia and reinforce the need for targeted, regionally adapted surveillance strategies that integrate multiple hosts and support early warning systems aligned with the One Health concept.