Silent Infection, Early Warning: Animals as Candidate Sentinels for Crimean–Congo Haemorrhagic Fever Surveillance—A Systematic Review

Crimean–Congo haemorrhagic fever virus (CCHFV) is a widely distributed tick-borne arbovirus maintained in an enzootic cycle involving wild and domestic mammals and ixodid ticks, particularly Hyalomma. This systematic review synthesised 390 eligible publication-level reports published from 2015 through 31 August 2026, comprising 351 independent quantitative reports and 39 linked/nonadditive publications. The evidence tables contained 150 animal, 106 tick and 180 human records across 69 countries. Serology dominated animal investigations; among reports with species-specific raw counts, antibody positivity was highest in camels (72.9%; 3918/5377 across 23 reports), followed by red deer (41.4%) and cattle (25.1%). Among 106 tick reports, CCHFV-positive Hyalomma and Rhipicephalus were reported in 80 (75.5%) and 41 (38.7%), respectively. Human sensitivity analyses yielded median estimates of 3.8% for antibody positivity, 13.6% for direct/composite viral detection and 20.0% for case fatality. These summaries are descriptive rather than pooled prevalence estimates. Overall, the evidence supports livestock and tick surveillance as complementary components of One Health surveillance, while prospective temporal studies are needed to establish predictive early-warning performance.