Possible Drivers of Crimean-Congo Hemorrhagic Fever Virus Transmission in Kosova

Spatial prediction of Crimean Congo hemorrhagic fever virus seroprevalence among livestock in Uganda

Crimean-Congo Hemorrhagic Fever (CCHF) is a viral disease that can infect humans via contact with tick vectors or livestock reservoirs and can cause moderate to severe disease. The first human case of CCHF in Uganda was identified in 2013. To determine the geographic distribution of the CCHF virus (CCHFV), serosampling among herds of livestock was conducted in 28 Uganda districts in 2017. A geostatistical model of CCHF seroprevalence among livestock was developed to incorporate environmental and anthropogenic variables associated with elevated CCHF seroprevalence to predict CCHF seroprevalence on a map of Uganda and estimate the probability that CCHF seroprevalence exceeded 30% at each prediction location. Environmental and anthropogenic variables were also analyzed in separate models to determine the spatially varying drivers of prediction and determine which covariate class resulted in best prediction certainty. Covariates used in the full model included distance to the nearest croplands, average annual change in night-time light index, percent sand soil content, land surface temperature, and enhanced vegetation index. Elevated CCHF seroprevalence occurred in patches throughout the country, being highest in northern Uganda. Environmental covariates drove predicted seroprevalence in the full model more than anthropogenic covariates. Combination of environmental and anthropogenic variables resulted in the best prediction certainty. An understanding of the spatial distribution of CCHF across Uganda and the variables that drove predictions can be used to prioritize specific locations and activities to reduce the risk of future CCHF transmission.

Systematic Review on Crimean–Congo Hemorrhagic Fever Enzootic Cycle and Factors Favoring Virus Transmission: Special Focus on France, an Apparently Free-Disease Area in Europe

Crimean–Congo hemorrhagic fever (CCHF) is a viral zoonotic disease resulting in hemorrhagic syndrome in humans. Its causative agent is naturally transmitted by ticks to non-human vertebrate hosts within an enzootic sylvatic cycle. Ticks are considered biological vectors, as well as reservoirs for CCHF virus (CCHFV), as they are able to maintain the virus for several months or even years and to transmit CCHFV to other ticks. Although animals are not symptomatic, some of them can sufficiently replicate the virus, becoming a source of infection for ticks as well as humans through direct contact with contaminated body fluids. The recent emergence of CCHF in Spain indicates that tick–human interaction rates promoting virus transmission are changing and lead to the emergence of CCHF. In other European countries such as France, the presence of one of its main tick vectors and the detection of antibodies targeting CCHFV in animals, at least in Corsica and in the absence of human cases, suggest that CCHFV could be spreading silently. In this review, we study the CCHFV epidemiological cycle as hypothesized in the French local context and select the most likely parameters that may influence virus transmission among tick vectors and non-human vertebrate hosts. For this, a total of 1,035 articles dating from 1957 to 2021 were selected for data extraction. This study made it possible to identify the tick species that seem to be the best candidate vectors of CCHFV in France, but also to highlight the importance of the abundance and composition of local host communities on vectors' infection prevalence. Regarding the presumed transmission cycle involving Hyalomma marginatum, as it might exist in France, at least in Corsica, it is assumed that tick vectors are still weakly infected and the probability of disease emergence in humans remains low. The likelihood of factors that may modify this equilibrium is discussed.

Transmission dynamics and vaccination strategies for Crimean-Congo haemorrhagic fever virus in Afghanistan: A modelling study

Background

Crimean-Congo haemorrhagic fever virus (CCHFV) is a highly pathogenic virus for which a safe and effective vaccine is not yet available, despite being considered a priority emerging pathogen. Understanding transmission patterns and the use of potential effective vaccines are central elements of the future plan against this infection.

Methods

We developed a series of models of transmission amongst livestock, and spillover infection into humans. We use real-world human and animal data from a CCHFV endemic area in Afghanistan (Herat) to calibrate our models. We assess the value of environmental drivers as proxy indicators of vector activity, and select the best model using deviance information criteria. Finally we assess the impact of vaccination by simulating campaigns targeted to humans or livestock, and to high-risk subpopulations (i.e, farmers).

Findings

Saturation deficit is the indicator that better explains tick activity trends in Herat. Recent increments in reported CCHFV cases in this area are more likely explained by increased surveillance capacity instead of changes in the background transmission dynamics. Modelling suggests that clinical cases only represent 31% (95% CrI 28%-33%) of total infections in this area. Vaccination campaigns targeting humans would result in a much larger impact than livestock vaccination (266 vs 31 clinical cases averted respectively) and a more efficient option when assessed in courses per case averted (35 vs 431 respectively). Targeted vaccination of farmers is impactful and more efficient, resulting in 19 courses per case averted (95% CrI 7–62) compared to targeting the general population (35 courses 95% CrI 16–107)

Conclusions

CCHFV is endemic in Herat, and transmission cycles are well predicted by environmental drivers like saturation deficit. Vaccinating humans is likely to be more efficient and impactful than animals, and importantly targeted interventions to high risk groups like farmers can offer a more efficient approach to vaccine roll-out.

Crimean-Congo haemorrhagic fever virus (CCHF) is an understudied emerging pathogen and the cause of increasingly frequent outbreaks of haemorrhagic fever in humans in several parts of the world. Here we bring together an important body of work in different aspects of the ecology and epidemiology of CCHF to shed light on its transmission dynamics into humans and the role of environmental drivers. These results show that over the years an endemic pattern of CCHFV transmission has been established within livestock, and the frequency of human cases mirrors the seasonal pattern of livestock transmission. Our analysis further suggests that an important fraction of cases in humans might be subclinical, and the volume of transmission into humans might be much larger than previously thought. We examine the potential impact of vaccination, which suggest that not only human vaccination could be more impactful than animal vaccination, but also that targeted strategies in human high risk groups could be very effective. Our results raise important insights for future vaccine development and important questions on the optimal conditions for conducting Phase III vaccine trials in humans.

Seroepidemiological Investigation of Crimean-Congo Hemorrhagic Fever Virus in Sheep and Camels of Inner Mongolia of China

Crimean-Congo hemorrhagic fever (CCHF) is a highly lethal infectious disease in humans caused by tick-borne Crimean-Congo hemorrhagic fever virus (CCHFV). To determine the potential risk of CCHF in the pastoral area of Northwestern China, the presence of antibody to CCHFV in the sera of two most common tick hosts, sheep and camels, in Inner Mongolia of China was evaluated. The purified recombinant nucleocapsid protein (NP) of CCHFV was prepared from a prokaryotic vector expressing the NP encoding gene, which was employed as the antigen to probe antibody against CCHFV in tick vectors using an immunoblotting assay. In total, 58.3% (35/60) and 54% (12/22) of camels were positive of antibody to CCHFV in sera at Alxa Youqi County and Ulan Hudu Gacha Village of Inner Mongolia Province, respectively. However, only 6.7% (2/30) of sera of sheep were determined positive in antibody to CCHFV in the Wulan Hudug check area in this study. Consequently, these results indicate that 54-58.3% camels were infected by CCHFV after exposure to tick bites in Inner Mongolia, which was significantly higher than 6.7% of infection in the sheep in this area, suggesting there is a certain relationship between the serological reactivity and exposure time to ticks, range of activity, living behaviors, and breeding time. Further intensive surveillance of livestock and exposed population is required to better understand the spread of CCHFV in this area.

Viral metagenomics, genetic and evolutionary characteristics of Crimean-Congo hemorrhagic fever orthonairovirus in humans, Kosovo

Crimean-Congo hemorrhagic fever orthonairovirus (CCHFV) is a tick-borne virus which causes severe disease in humans with fatality cases up to 30%. We investigated the genetic and evolutionary characteristics of CCHFV in Kosovo, in particular in humans and found that different virus variants of genotype V circulate, with Turkey as a possible origin for the progenitor of southern European CCHF outbreaks. Phylogenetic analyses also revealed a single introduction event and in situ evolution of CCHFV in this country. The viral metagenomics revealed a more abundant virome in the fatal CCHF cases and the presence of a novel tick-borne segmented RNA virus belonging to the recently discovered Jingmenvirus group which raises questions about the potential pathogenic effect of this novel virus on human and animal health.

Identifying main drivers and testing control strategies for CCHFV spread

Crimean Congo Haemorrhagic Fever (CCHF) is an emerging zoonotic disease. The causative agent is a virus (CCHFV), mainly transmitted by ticks of the species Hyalomma marginatum in Eastern Europe and Turkey. In order to test potential scenarios for the control of pathogen spread, the basic reproduction number (R0) for CCHF was calculated. This calculation was based on a population dynamics model and parameter values from the literature for pathogen transmission. The tick population dynamics model takes into account the major processes involved and gives estimates for tick survival from one stage to the other and number of feeding ticks. It also considers the influence of abiotic (meteorological variables) and biotic factors (host densities) on model outputs, which were compared with data collected in Central Anatolia (Turkey). R0 computation was thereafter used to test control strategies and especially the effect of acaricide treatment. Simulation results indicate that such treatments could have valuable effects provided that the acaricide is applied regularly throughout the spring and summer, and over several years. Furthermore, a sensitivity analysis to abiotic and biotic factors showed that, even though temperature has a strong impact on model outputs, host (mainly hare) densities also play a role. The kind of model we have developed provides insight into the ability of different strategies to prevent and control disease spread and has proved its relevance when associated with field trials.

Crimean-Congo hemorrhagic fever in Turkey: Current status and future challenges

Crimean-Congo hemorrhagic fever (CCHF) is a tick-borne viral disease of humans that affects a wide geographic area of Africa and Eurasia, including Turkey, Iran, Pakistan, Afghanistan and Russia. Since the first detection of CCHF cases in Turkey in 2002, more than 9700 patients have been reported, with an overall mortality rate just under 5%. This article assesses the present epidemiological situation of CCHF in Turkey, with an updated literature review, describes national practices and summarizes lessons learned in preparation for future outbreaks.

Consensus report: Preventive measures for Crimean-Congo Hemorrhagic Fever during Eid-al-Adha festival

Crimean-Congo hemorrhagic fever (CCHF) is endemic in Eurasian countries such as, Turkey, Pakistan, Afghanistan and Iran. CCHF virus is spread by the Hyalomma tick, which is found mainly on cattle and sheep. Muslim countries, in which these animals are sacrificed during Eid-Al-Adha, are among the countries where CCHF is endemic, and it has been observed that CCHF is associated with practices surrounding the Eid-ad-Adha festival. The dates for Eid-Al-Adha drift 10 days earlier in each year according to Georgian calendar. In previous years Eid-al-Adha occurred in autumn-winter months however in the next 10-15 years it will be take place in the summer months when CCHF is more prevalent. This may lead to a rise in the number of cases due to increased dissemination of CCHF virus with uncontrolled animal movements in and between countries. This consensus report focuses on the variable practices regarding animal handling in different regions and possible preventative measures to reduce the incidence of CCHF. Environmental hygiene and personal protection are essential parts of prevention. There is a need for international collaborative preparedness and response plans for prevention and management of CCHF during Eid-Al-Adha in countries where the disease is prevalent.

Crimean-Congo hemorrhagic fever virus clades V and VI (Europe 1 and 2) in ticks in Kosovo, 2012

Despite being a small country, Kosovo represents one of the few foci of Crimean-Congo hemorrhagic fever (CCHF) in Europe. The distribution of Kosovar tick vectors and the evolution of CCHF virus in ticks are both as yet unknown. A better description of the extent and the genetic diversity of CCHFV in ticks from endemic settings is essential, in order to be controlled. We investigated the 2012 distribution of Kosovar ticks alongside the prevalence and the phylogeography of tick-derived CCHFV. Hyalomma marginatum dominated in the endemic municipalities with 90.2% versus 24.3% in the non-endemic regions. Of 1,102 tested ticks, 40 (3.6%) were CCHFV-positive, belonging to H. marginatum (29), Rhipicephalus bursa (10), and Ixodes ricinus (1). The virus strains clustered with clade V and VI related sequences. They fell into two lineages: Kosovo I and II. Kosovo I comprised strains recovered exclusively from R. bursa ticks and was closely related to AP92 prototype strain. Kosovo II clustered into Kosovo IIa, including human-derived strains, and IIb including only strains detected in H. marginatum and I. ricinus. Our phylogeographic reconstruction suggests two temporally distinct CCHFV introductions: the most probable location of the most recent common ancestor of Kosovo I lineage was in Greece (63 years ago) and that of lineages IIa-b in Turkey (35 years ago). After each CCHFV introduction into Kosovo, subsequent lineage expansions suggest periods of in situ evolution. The study provides the first insight into the genetic variability and the origin of CCHFV in ticks from Kosovo. Our findings indicate the spreading of CCHFV to non-endemic areas, which underlines the importance of further studies in order to monitor and predict future CCHF outbreaks in Kosovo. The AP92-like strains appear to be more widespread than previously thought and may provide a promising target for experimental studies due to their assumed low pathogenicity.

Crimean-Congo hemorrhagic fever virus (CCHFV) is the most widespread tick-borne virus affecting humans. Its distribution coincides with that of Old World Hyalomma tick vectors. The virus circulates in an enzootic cycle, where hard ticks are both vectors and reservoirs, and mammals the amplifying hosts. Accidentally, humans become infected as dead-end hosts. One of the few CCHF-endemic European countries is Kosovo, where an annual average of ten sporadic cases, with a mean mortality rate of 18%, are reported. In this study, the tick distribution, CCHFV prevalence and the phylogeography of the tick-derived strains from 2012 were investigated. The majority of ticks belonged to Hyalomma marginatum, the main vector of CCHFV. Indeed, of 40 CCHFV-positive ticks, 29 were H. marginatum. The phylogenetic analyses revealed that 30 viral strains formed a distinct lineage within clade V (Europe 1) and were closely related to previously known strains from humans and ticks from the Balkans. However, ten isolates from Rhipicephalus bursa ticks, collected in a non-endemic region, turned out to cluster within a very divergent CCHFV clade (Europe 2), so far only known from Greece and Turkey. Since these strains presumably develop only subclinical or mild infections in humans, they might be suitable for experimental vaccine studies.

Bayesian phylogeography of Crimean-Congo hemorrhagic fever virus in Europe

Crimean-Congo hemorrhagic fever (CCHF) is a zoonosis mainly transmitted by ticks that causes severe hemorrhagic fever and has a mortality rate of 5-60%. The first outbreak of CCHF occurred in the Crimean peninsula in 1944-45 and it has recently emerged in the Balkans and eastern Mediterranean. In order to reconstruct the origin and pathway of the worldwide dispersion of the virus at global and regional (eastern European) level, we investigated the phylogeography of the infection by analysing 121 publicly available CCHFV S gene sequences including two recently characterised Albanian isolates. The spatial and temporal phylogeny was reconstructed using a Bayesian Markov chain Monte Carlo approach, which estimated a mean evolutionary rate of 2.96 x 10^-4 (95%HPD=1.6 and 4.7 x 10^-4) substitutions/site/year for the analysed fragment. All of the isolates segregated into seven highly significant clades that correspond to the known geographical clades: in particular the two new isolates from northern Albania clustered significantly within the Europe 1 clade. Our phylogeographical reconstruction suggests that the global CCHFV clades originated about one thousand years ago from a common ancestor probably located in Africa. The virus then spread to Asia in the XV century and entered Europe on at least two occasions: the first in the early 1800s, when a still circulating but less or non-pathogenic virus emerged in Greece and Turkey, and the second in the early 1900s, when a pathogenic CCHFV strain began to spread in eastern Europe. The most probable location for the origin of this European clade 1 was Russia, but Turkey played a central role in spreading the virus throughout Europe. Given the close proximity of the infected areas, our data suggest that the movement of wild and domestic ungulates from endemic areas was probably the main cause of the dissemination of the virus in eastern Europe.

Seroprevalence and risk factors of Crimean-Congo hemorrhagic fever in selected seven provinces in Turkey

Turkey has been one of the most endemic regions since 2002, when Crimean-Congo hemorrhagic fever emerged worldwide. The aim of the present study was to estimate the seroprevelance of CCHF virus in humans who reside in rural and urban areas of known endemic and nonendemic selected provinces of Turkey by using commercial ELISA kit. CCHFV IgG antibodies were detected in 2.3% of the population. The most important risk factors for CCHF seropositivity, were older age, male gender, illiterate, farmer, animal husbandry, living in rural residence in adobe houses, and a previous tick bite history.

Epidemiological and behavioral factors associated with Crimean-Congo hemorrhagic fever virus infections in humans

Crimean-Congo hemorrhagic fever (CCHF), a viral disease with high fatality rate, is endemic in many countries in Europe, the Middle East, Asia and Africa. It is transmitted to humans either by tick bite or by direct contact with blood or tissues of viremic patients or livestock. Aim of the present study was to review the main epidemiological characteristics of the disease worldwide, with special attempt to show the epidemiological and behavioral factors that play a role in acquisition of the infection. It is obvious that these factors differ among countries, and the knowledge and understanding of the transmission routes in each region facilitates the implementation of proper control measures, the awareness enhancement and the prevention of the disease.

The impact of Crimean-Congo hemorrhagic fever virus on public health

Climatic, environmental and economic changes, as well as the steadily increasing global trade and personal mobility provide ample opportunities for emerging pathogens with zoonotic potential to spread to previously unaffected countries. Crimean-Congo hemorrhagic fever virus (CCHFV) is considered to be one of the major emerging disease threats spreading to and within the European Union following an expanding distribution of its main vector, ticks of the genus Hyalomma. Every year more than 1000 human CCHF cases are reported from countries of southeastern Europe and Turkey. CCHFV can cause high case fatality rates and can be transmitted from human to human. There are no vaccine prophylaxis and therapeutic interventions available at present. Several EU-funded research projects focus currently on CCHFV which highlights the awareness for this problem at the European level. As public health deals with questions of prevention on a population level rather than healing and health on an individual level, the analysis of existing data plays a fundamental role to minimize its epidemic potential, by reducing infection risks, and to manage disease outbreaks. This review gives a summary of the current knowledge and data with focus at the interface between public health and CCHFV. Based on this knowledge, guidelines for the risk classification of a region and for outbreak prevention are given. This review will assist decision makers and public health authorities in understanding risk scenarios and in deciding on effective countermeasures, as well as human and veterinary scientists by highlighting existing gaps in knowledge.

Importation of Hyalomma marginatum, vector of Crimean-Congo haemorrhagic fever virus, into the United Kingdom by migratory birds

Hyalomma marginatum ticks are an important vector of Crimean-Congo haemorrhagic fever virus which can result in a severe and potentially fatal disease in humans. Given the continued emergence of clinical cases in Eurasia and focalised upsurges of H. marginatum populations in Europe, it seemed prudent to assess the potential of this vector species to be introduced into the United Kingdom. Immature forms of H. marginatum are frequent ectoparasites of passerine birds many of which migrate from Africa to the UK each spring. Incoming birds were inspected for ticks during the spring migration in 2010 and 2011. A total of 68 ticks was collected from 971 birds (29 bird species), 21% (14) of the ticks were identified as H. marginatum. Oenanthe oenanthe (Northern wheatear) and Sylvia communis (Whitethroat) were found to be infested by this tick in both years and with multiple ticks. Single specimens were also removed from Acrocephalus schoenobaenus (Sedge warbler) and Phoenicurus phoenicurus (Common redstart) in 2010. This study provides the first contemporary evidence for substantial importation of this tick species into the UK.