Crimean-Congo hemorrhagic fever in Iran: a systematic review of viral detection in ticks, vector distribution, and data gaps for health system decision-makers.

BACKGROUND

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne viral zoonosis reported in Iran, where hard ticks serve as both reservoirs and vectors for Crimean-Congo hemorrhagic fever virus (CCHFV). Understanding the geographic distribution and infection prevalence in tick populations is essential for evidence-based surveillance and control strategies.

METHODS

Following PRISMA guidelines, a systematic literature search was conducted for studies reporting CCHFV detection in hard ticks from Iranian provinces up to December 2023. Data on province, tick species, infection rate, detection method, sample size, host animal, and collection date were extracted.

RESULTS

From 86 studies spanning 1978-2023, available data permitted provisional stratification of Iranian provinces into four categories based on reported infection rates: highest reported rates (Ardabil: 30.5-33.3%; Chaharmahal and Bakhtiari: 22.6-22.8%; Hamadan: 15.6-19.2%); intermediate reported rates (eight provinces: 5-10%); lowest reported rates (seven provinces: <5%); and insufficient data (seven provinces with limited or no surveillance). Fourteen tick species across four genera were reported infected, with Hyalomma marginatum and Hyalomma anatolicum most frequently identified. Based on available studies, ticks collected from camels showed the highest reported infection burden (23.8%), followed by sheep (10.2%), goats (9.0%), and cattle (8.5%). A random-effects meta-analysis of 75 species-specific samplings yielded a pooled infection rate of 3.1% (95% CI: 2.3-4.2%) with substantial heterogeneity (I² = 93.8%). A decreasing temporal trend was observed from 2010 to 2019, although this finding is subject to important caveats, including changes in surveillance intensity, sampling methods, and geographic coverage.

CONCLUSIONS

This synthesis provides a geospatial and ecological baseline for CCHFV in ticks, identifying substantial geographic heterogeneity and critical surveillance gaps. The proposed risk categories are provisional and require prospective validation with standardized sampling. Decision-makers should interpret reported infection rates cautiously given significant methodological heterogeneity across studies and should prioritize filling data gaps in provinces with limited surveillance before allocating control resources. Importantly, tick infection prevalence represents only one component of zoonotic risk; comprehensive risk assessment requires integration with human exposure data, case reports, and environmental factors.