Probable Vector of Crimean-Congo Hemorrhagic Fever Virus; Hyalomma aegyptium: A Systematic Review and Meta-Analysis

Abstract

Introduction: Crimean-Congo hemorrhagic fever (CCHF) is the widest emerging severe viral tick-borne disease affecting humans. Crimean-Congo haemorrhagic fever virus (CCHFV) circulates by routine enzootic tick-vertebrate hosts-tick transmission cycles. We aimed to evaluate the molecular prevalence of CCHFV in ticks on a global scale. Methods: A systematic procedure was used to perform this review and meta-analysis using PubMed, Google Scholar, and Web of Science databases from 1 January 2000 through 12 April 2023. Of the 2310 papers identified, 43 articles met the inclusion criteria for this study. Results: The overall prevalence of CCHFV was 4.0% (95%CI: 2.7–6.0%) in ticks on the global scale, with heterogeneity (I²=96.387; p=0.0001). The genus Hyalommawas shown as the most frequent tick infected with CCHFV 5.4% (95%CI: 3.3–8.7%). We found that the pooled prevalence of CCHFV was higher in Hyalomma aegyptium 27.6% (95%CI: 22.7–33.2%). The pooled prevalence was higher in Asia 5.1% (95%CI: 3.3–7.7%), and Spain 21.0% (95%CI: 3.4–66.9). The locations with annual rainfall of 401-1000 mm 6.1% (95%CI: 2.6–13.5%) and latitude of 31-40° 6.0% (95%CI: 4.1–8.9%) were associated with the greatest pooled prevalence of CCHFV in ticks. Conclusions: Surveillance of CCHFV in ticks will give a better comprehension for the future implementation of public health interventions. The question of whether Hyalomma aegyptium is a plausible or certain vector should be the subject of further investigation.

Introduction

The Crimean-Congo haemorrhagic fever virus (CCHFV) belongs to the genus Orthonairovirusof the family Nairoviridae [1]. Crimean-Congo hemorrhagic fever (CCHF) is a severe tick-borne illness, emerged as public health concern in endemic countries [2]. CCHFV is widespread in Africa, parts of Asia, the Middle East, and Southeastern Europe [3,4]. CCHF virus is associated with severe hemorrhagic fever with high mortality from 5 to 50%. Epidemiologically, CCHFV has been reported as potentially endemic or endemic in about 50 countries [5]. The virus spreads in wildlife in an enzootic tick-vertebrate-tick pattern, and human infection occurs both by tick bites and direct contact with tissues or blood from viremic animals or patients [6]. Asymptomatic CCHF hosts, such as domestic and wild animals in the endemic CCHF transitional cycle, are necessary for tick feeding via transstadial, transovarian, and venereal transmission, which helps disseminate the virus to new tick colonies [7,8]. In the living cycle of CCHFV, ticks may take action not only as vectors, but also as reservoirs [9,10]. Goats and sheep are known as possible farm animal indicators for the circulation of CCHFV [9]Molecular methods such as polymerase chain reaction (PCR) have been a major advance in the scientific world for the detection of CCHFV [11]. In addition, detection of virus by reverse transcription polymerase chain reaction (RT-PCR) is necessary to confirm a real circulation of CCHFV [12]. Various studies have been conducted to estimate the prevalence of CCHFV in several areas of the world at different times. However, evaluating the prevalence of tick infection with CCHFV globally seems necessary. This study specifies the pooled molecular prevalence of CCHFV in ticks using RT-PCR on a global scale with regard to types of ticks, continents, countries, annual rainfall and latitude.

Methods

Search strategy

In order to assess the global epidemiological state of CCHFV in ticks, we perfeormed a systematic review by searching online English-language literature. We used the PRISMA recommendations (available at: http://www.prisma-statement.org/) for this. Using the databases PubMed, Google Scholar, and Web of Science, an extensive literature search was conducted to find pertinent works published between 1 January 2000 and 12 April 2023. In order to find publications that used RT-PCR to estimate the prevalence of CCHFV in ticks, an extensive search was conducted. In the next step, special keywords or phrases including CCHF, RT-PCR, and ticks were selected alone or in combination with “OR” and/or “AND” operators. The searches were re-run just before the final analyses to retrieve the most recent eligible studies for inclusion. Published papers with epidemiologic results were selected. All selected papers were imported in Endnote version X9 (Clarivate Analytics, USA). English language and ticks were considered as the limitations of language and study group respectively.

Eligibility criteria

The following criteria were satisfied for a paper to be considered for additional analysis: (a) studies on single CCHFV-infected ticks; (b) studies that used RT-PCR to assess the prevalence of CCHFV based on tick species; (c) studies reporting the number of positive samples; (d) full-text publications published in the English language without regard to location; and (e) studies designing cross-sectional studies. Papers meeting the following criteria were excluded: papers reporting the pooled prevalence of CCHFV in ticks, review papers, posters, clinical trials, cohort studies, letters to the editor, case report articles, meeting abstracts, congress, case-control studies, empirical research, perplexing studies, unpublished studies, and brief communication papers. To incorporate all relevant and potential papers, references to systematic reviews and meta-analyses were checked. To estimate the actual overall prevalence of CCHFV in different types of ticks, after pooling the results of the studies, types of ticks with a sample size of <30 ticks were not considered.

Data extraction

Two researchers contributed to the data elicitation (HS and SGK) separately from included investigations through a pretested and modulated format provided in Microsoft Excel. The following specifications of each associated study were elicited: first author, year of publication, country, type of samples, number of sample size, number of positive samples, type of study, prevalence of CCHFV, and method. Based on tick species, continent, country, and genus, subgroup analyses were carried out to investigate heterogeneity for analysis. Disagreements between researchers were resolved by the decision of a third reviewer (MA).

Quality assessment

The included papers’ quality was assessed using Newcastle-Ottawa Scale [13]. The quality was calculated using 10 points for each paper according to subject selection (0–5 points), comparability of subjects (0–2 points) and outcome (0–3 points). A total score of 0–4, 5–6, 7–8, and 9–10 points was labelled Unsatisfactory Studies, Satisfactory Studies, Good Studies and Very Good Studies, respectively [14].

Statistical analysis

All statistical analyses were conducted using Comprehensive Meta-Analysis Software (CMA version 3). Forest plot, funnel plot, tables, and figures were used to describe the original papers. A random-effects model was used to account for potential heterogeneity among studies. The pooled prevalence of CCHFV in ticks was computed with 95% confidence intervals (CIs). Heterogeneity index (I²statistics) was employed to compute heterogeneity among the papers. I²values of <25%, 50% and <75% were known as low, moderate and high heterogeneity, respectively [15]. Using Egger regression test-based funnel plots, we evaluated the publication bias. An evaluation of the effect of the year of publication on prevalence was conducted using a meta-regression analysis. A p-value <0.05 was considered statistically significant.

Results

Literature search, selection and data extraction

An electronic database search produced a total of 2310 published papers. A total of 105 full-text articles were chosen for eligibility evaluation. Sixty-two full-text papers were excluded with reasons including paper’s reported pooled prevalence, reviews, unclear data, and not relevant data. Ultimately, 43 studies were included in the meta-analysis according to critical assessment criteria (Figure 1, Supplementary Table 1).

The included studies that utilized molecular techniques based on RT-PCR methods in individual ticks. Included papers displayed high heterogeneity based on I²test (I²=96.387%, p<0.0001), which is suggestive to use random effects model.

Pooled prevalence

The assessed global pooled molecular prevalence for CCHFV in ticks was 4.0% (95%CI: 2.7–6.0%)—Figure 2.

Hyalomma was the most abundant genus of ticks infected with CCHFV (5.4%; 95%CI: 3.3–8.7%)—Figure 3.

Concerning the species of the ticks, the top three evaluated pooled prevalences were as follows: 27.6% (95%CI: 22.7–33.2%) for Hyalomma aegyptium, 20.2% (95%CI: 17.2–23.6%) for Hyalomma lusitanicum and 11.3% (95%CI: 8.8–14.5%)—Supplementary Figure 1.

The analysis based on continents showed that the infection was most prevalent in Asia 5.1% (95%CI: 3.3–7.8%), Europe 3.8% (95%CI: 1.5–9.2%) and Africa 1.0% (95%CI: 0.3–3.3%)—Supplementary Figure 2.

A subgroup analysis based on country showed some differences in CCHFV prevalence. The evaluated pooled prevalence of CCHFV was highest in Spain (21%; 95%CI: 3.4–66.9%), however, it was based only on one study. It was 8.9% (95%CI: 3.5–21.0%) in Turkey, and 5.3% (95%CI: 3.4–8.1%) in Iran—Supplementary Figure 3.

Furthermore, the infection was more prevalent in regions with Annual rainfall 401-1000 mm 6.1% (95%CI: 2.6–13.5%) and Latitude 31-40° 6.0% (95%CI: 4.1-8.9%)—Supplementary Figure 4 and Figure 5.

According to the papers included in the analysis, molecular prevalence of CCHFV infection in individual ticks has been documented in 11 countries. The largest number of studies was performed in Iran (25 studies), followed by Turkey (5 studies).

Publication bias

The funnel plot (Supplementary Figure 6) shows evidence of publication bias.

Egger’s test for a regression intercept gave a p-value of 0.0005, indicating evidence of publication bias (Supplementary Figure 7).

Meta-regression analysis revealed no evidence of heterogeneity between studies regarding the year of publication (p=0.055)—Supplementary Figure 8.

Evaluation of study quality indicated that of 43 studies, 6 had a total score of 0-4 points (Unsatisfactory Studies), 33 had a total score of 5-6 points (Satisfactory Studies), and 4 had a total score of 7-8 points (Good Studies). There were no Very Good Studies among the ones included. (Supplementary Table 2).

Discussion

Similar to leishmaniosis, cockroaches, pediculosis, scabies, and myiasis, tick-borne diseases endanger human health [16,17]. Like other tick-borne zoonotic pathogens, CCHFV circulates in the enzootic pattern of tick–vertebrate–tick transmission, which indicates that the epidemiology of CCHF is extremely complicated [18]. In other words, surveillance of CCHFV in ticks could yield useful information concerning evaluating the risk of exposure in humans, recognizing the natural host, and forecasting future CCHV outbreaks [19], especially in places that are CCHF endemic [20].

Diverse ticks of invertebrate and various vertebrate animals are involved in the CCHF life cycle [21]. Because of the importance of the geographical diversity of tick species in various areas [22], we evaluated the pooled molecular prevalence of CCHFV globally in ticks. Subgroup analysis was carried out to explore heterogeneity based on genus of ticks, tick species, continent, country, annual rainfall, and latitude. Based on epidemiological studies, CCHFV is transmitted more by Hyalomma genus ticks [23]. The general occurrence of CCHF in Asia, Europe, and Africa parallels the distribution of Hyalomma ticks worldwide [9]. In this study Hyalomma was found the most abundant genus of ticks infected with CCHFV (5.4%; 95%CI: 3.3–8.7%). We included studies that reported the presence of CCHFV in individual ticks on the account that it is a precious approach to obtain real prevalence of the CCHFV in ticks compared to reporting presence of CCHFV in pooled ticks [24]. Findings show molecular prevalence of CCHFV in ticks being documented in 43 papers from 11 countries. CCHF is usually seen in Asia, the Middle East, Southeast Europe, and Africa. No related published papers were included for America, and Australia. The current systematic review presents the global pooled prevalence of CCHFV (4.0%; 95%CI: 2.7–6.0%), with heterogeneity (I²=96.387; p<0.0001) in ticks based on RT-PCR. Results of this study also show that infection with CCHFV in ticks is limited to the three continents (Asia, Europe, and Africa), which is related to our type of study. The prevalence ranged widely from 0.1% to 51.5% for various studies that satisfied the current review’s inclusion requirements. These changes are associated with the geographical factors in various parts of the world [25]. The global CCHFV infection in ticks exhibited a decreasing trend [26]. Our findings also show signs of a decline in CCHFV infection in ticks throughout the roughly ten years covered by published studies. (Supplementary Figure 9).

Ticks of the genus Hyalomma, markedly Hyalomma marginatum, are believed to be the main vectors of CCHFV [27]. It is indicated thatHyalomma aegyptium potentially has a cryptic transmission cycle with a key role in preserving the virus in the wild world [28]. Therefore, this approach to systematic meta-analysis review looks to summarize the role ofHyalomma aegyptium as a probable vector of CCHFV. Although the studies are limited on assessing the prevalence of CCHFV on Hyalomma aegyptiumin nature, this meta-analysis revealed that Hyalomma aegyptium is the most frequent species infected with CCHFV (27.6%; 95%CI: 22.7–33.2%). This makes and highlights the query of whether or not Hyalomma aegyptiumplays a part in the natural transmission dynamics of CCHFV.

Strengths and limitations

RT-PCR is used in this systematic review and meta-analysis to assess the global prevalence of CCHFV in individual ticks. The strengths of this meta-analysis strengths include a thorough literature search, precise methodology, clearly defined exclusion and inclusion criteria, and quality assessment by two independent reviewers. However, some limitations exist due to the nature of the investigations. One of the limitations of this study was evaluating the prevalence of CCHFV in individual not in pooled ticks.

Conclusions

The meta-analysis provided here gives us an adequate comprehension of the global spread of CCHFV among ticks. Even the largest investigation is never able to rule out a very small effect, an important effect can only ever be shown to be negligible, not non-existent. Accordingly, further research should focus on Hyalomma aegyptium to answer this query of whether Hyalomma aegyptium is a probable or a certain vector.