Infectious Disease · Medical Literature
Crimean-Congo hemorrhagic fever in Iran: a systematic review of viral detection in ticks, vector distribution, and data gaps for health system decision-makers.
Abstract
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. 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. 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. 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.
Clinical relevance
What is the geographic distribution and CCHFV infection prevalence across Iranian provinces in hard tick populations, and what surveillance gaps exist that are relevant to health system decision-making? __SNAPSHOT__ {"studyDesign":"Systematic review (PRISMA-guided) of published studies reporting CCHFV detection in hard ticks across Iranian provinces","setting":"Iran (all provinces); multi-site, population-based entomological surveillance data aggregated from published literature spanning 1978–2023","sampleSize":"86 studies included; individual tick sample sizes vary by constituent study and are not aggregated in the abstract","population":"Hard tick (Ixodidae) populations collected from Iranian provinces; associated host animals include domestic livestock (sheep, cattle, goats, camels) and other vertebrate hosts","intervention":"Systematic aggregation and provincial stratification of CCHFV detection data from hard ticks, including infection rate, tick species, detection method, host animal, collection date, and geographic location","comparator":"Not applicable (single-arm descriptive systematic review; provinces compared descriptively by infection rate tier)","primaryOutcome":"CCHFV infection rate in hard tick populations, stratified by Iranian province and tick species, using reported molecular or virological detection methods","followUp":"Literature coverage: 1978–December 2023 (approximately 45 years of surveillance data)","fundingSource":"Not reported"}
Key findings
From 86 studies spanning 1978–2023, the review provisionally stratified Iran's provinces into four CCHFV infection rate tiers based on available tick surveillance data. Highest reported rates were identified in Ardabil (30.5–33.3%), Chaharmahal and Bakhtiari (22.6–22.8%), and Hamadan (15.6–19.2%). Eight provinces fell into an intermediate tier (5–10% infection rate), seven provinces into a lowest tier (<5%), and seven provinces had insufficient or absent surveillance data precluding meaningful classification. Fourteen tick species across four genera were reported to carry CCHFV, with Hyalomma marginatum and Hyalomma anatolicum identified as the most prominently infected species (the abstract was truncated and did not fully report all species-level findings). No pooled infection rate with confidence intervals or aggregate p-values across all provinces was reported in the abstract. Individual study-level statistical measures were not extractable from the abstract. NNT/NNH are not applicable to this study design.
Practice implications
This systematic review establishes a province-level risk map for CCHFV tick reservoir burden in Iran, providing decision-relevant data for surveillance prioritization, veterinary public health resource allocation, and occupational risk stratification. The finding that three provinces (Ardabil, Chaharmahal and Bakhtiari, Hamadan) carry infection rates exceeding 15% in tick populations is clinically and epidemiologically significant, as these figures substantially exceed the pooled national estimate of approximately 6% reported in a prior meta-analysis of Iranian tick data. Importantly, seven provinces had insufficient surveillance data, meaning true endemicity in those regions cannot be excluded—a critical gap for health authorities who must plan tick control, livestock inspection, and case detection programs. The review does not establish causative links between tick infection rates and human case incidence within specific provinces, nor does it report human exposure risk estimates, seroprevalence, or clinical outcome data. Findings apply to vector surveillance contexts; they do not directly quantify individual patient risk. CCHF remains a WHO-prioritized disease with no approved vaccine and limited antiviral options. This review is based only on the available abstract, and full-text review may reveal additional methodological details, quality assessments, or subgroup analyses not captured here. __LIMITATIONS__ 1. Only the abstract was available for this summary; full methodological details, quality-of-evidence assessments (e.g., GRADE or Newcastle-Ottawa), heterogeneity analyses, and sensitivity analyses could not be evaluated. 2. The 86 constituent studies span 45 years (1978–2023), introducing substantial temporal heterogeneity; tick infection rates in earlier studies may reflect different viral strains, detection methods (e.g., older virus isolation vs. contemporary RT-PCR), and ecological conditions that are not directly comparable. 3. Provincial infection rate 'tiers' are described as provisional, reflecting uneven geographic sampling density rather than true population-representative estimates; provinces with sparse sampling may be systematically misclassified. 4. Detection method heterogeneity (RT-PCR, virus isolation, and potentially other techniques) across constituent studies may affect comparability of infection rates. 5. Seven provinces with insufficient data represent a structural surveillance blind spot that limits generalizability of the national risk map. 6. The review focuses exclusively on vector infection rates and does not integrate human case data, seroprevalence, or ecological covariates (e.g., altitude, climate, livestock density) needed for full transmission risk modeling. 7. Potential for publication bias toward provinces with known or suspected CCHF activity, inflating apparent geographic heterogeneity. 8. Funding source not reported, limiting assessment of potential conflicts of interest. __BOTTOM_LINE_CATEGORY__ promising_but_preliminary __BOTTOM_LINE__ This PRISMA-guided systematic review of 86 studies identifies marked interprovincial variation in CCHFV infection rates among Iranian hard ticks, with Ardabil, Chaharmahal and Bakhtiari, and Hamadan provinces showing the highest reported rates (>15%), while seven provinces lack adequate surveillance data. Hyalomma marginatum and Hyalomma anatolicum are the predominant infected tick species. For infectious disease and public health practitioners, these findings support risk-stratified tick surveillance and occupational health interventions in high-rate provinces, while highlighting an urgent need for systematic entomological surveys in data-deficient regions before confident national CCHF risk mapping can be achieved.