Epidemiological investigation of Crimean-Congo haemorrhagic fever virus infection among the one-humped camels (Camelus dromedarius) in southern Tunisia

A Review on Crimean-Congo Hemorrhagic Fever Infections in Tunisia

Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic tick-borne disease, caused by an arbovirus of the genus Orthonairovirus and the family Nairoviridae. Crimean-Congo hemorrhagic fever virus (CCHFV) is widespread in several regions of the world. While the virus is not pathogenic to all susceptible livestock and wild mammals, it can lead to severe hemorrhagic fever in humans. In this review, we compiled published data on CCHFV infections in humans, animals, and ticks in Tunisia. Based on that, we discussed the epidemiology and the distribution patterns of CCHFV infections highlighting the risk factors for this virus in the country. CCHF infection prevalence in humans was estimated to 2.76% (5/181) and 5% (2/38) in Tunisian febrile patients and Tunisian slaughterhouse workers, respectively. Concurrently, seroprevalence in domestic ungulates (sheep, goats, cattle, and dromedaries) ranged from zero to 89.7%, and only one Hyalomma impeltatum tick specimen collected from dromedaries in southern Tunisian was positive for CCHFV by reverse transcriptase-polymerase chain reaction (0.6%; 1/165). As Tunisian studies on CCHFV are geographically scattered and limited due to very small sample sizes, further studies are needed to improve the knowledge on the epidemiology of CCHF in Tunisia.

Epidemiologic Survey of Crimean-Congo Hemorrhagic Fever Virus in Suids, Spain

We conducted a cross-sectional study in wild boar and extensively managed Iberian pig populations in a hotspot area of Crimean-Congo hemorrhagic fever virus (CCHFV) in Spain. We tested for antibodies against CCHFV by using 2 ELISAs in parallel. We assessed the presence of CCHFV RNA by means of reverse transcription quantitative PCR protocol, which detects all genotypes. A total of 113 (21.8%) of 518 suids sampled showed antibodies against CCHFV by ELISA. By species, 106 (39.7%) of 267 wild boars and 7 (2.8%) of 251 Iberian pigs analyzed were seropositive. Of the 231 Iberian pigs and 231 wild boars analyzed, none tested positive for CCHFV RNA. These findings indicate high CCHFV exposure in wild boar populations in endemic areas and confirm the susceptibility of extensively reared pigs to CCHFV, even though they may only play a limited role in the enzootic cycle.

In vitro feeding of all life stages of two-host Hyalomma excavatum and Hyalomma scupense and three-host Hyalomma dromedarii ticks

Ticks are blood-sucking ectoparasites and can transmit various pathogens of medical and veterinary relevance. The life cycle of ticks can be completed under laboratory conditions on experimental animals, but the artificial feeding of ticks has attracted increased interest as an alternative method. This study represents the first report on the successful in vitro feeding of all life stages of two-host tick species, Hyalomma scupense and Hyalomma excavatum, and the three-host tick Hyalomma dromedarii. The attachment and engorgement rates of adults were 84% (21/25) and 76% (19/25) for H. scupense females. For adult H. excavatum and H. dromedarii, 70% (21/30) and 34.4% (11/32) of the females attached and all attached females successfully fed to repletion. The oviposition rates of the artificially fed females were 36.4%, 57.1% and 63.1% for H. dromedarii, H. excavatum and H. scupense, respectively, with a reproductive efficiency index varying between 44.3 and 60.7%. For the larvae, the attachment and engorgement rates were 44.2% (313/708) and 42.8% (303/708) for H. dromedarii, 70.5% (129/183) and 56.8% (104/183) for H. excavatum and 92.6% (113/122) and 55.7% (68/122) for H. scupense. The attachment and engorgement rates for the nymphs were 90.2% (129/143) and 47.6% (68/143) for H. dromedarii, 66.7% (34/51) and 41.2% (21/51) for H. excavatum, and 44.1% (30/68) and 36.8% (25/68) for H. scupense. Molting rates of the immature stages varied between 71.3% (216/303) and 100% (68/68) for the larvae and between 61.9% (13/21) and 96% (24/25) for the nymphs. The successful in vitro feeding of all stages of the three Hyalomma species makes this method a valuable tool for tick research, with potential applications in studies on the pathogens transmitted by these tick species such as Theileria annulata.

Tick-borne pathogens in camels: A systematic review and meta-analysis of the prevalence in dromedaries

Published data on tick-borne pathogens (TBPs) in camels worldwide have been collected to provide an overview of the global prevalence and species diversity of camelid TBPs. Several TBPs have been detected in dromedary camels, raising concerns regarding their role as natural or maintenance hosts for tick-borne pathogens. Insubstantial evidence exists regarding the natural infection of camels with Babesia spp., Theileria spp., Anaplasma spp., and Ehrlichia spp., particularly because most of the camels were considered healthy at the time of sampling. Based on polymerase chain reaction (PCR) testing, a pooled prevalence of 35.3% (95% CI: 22.6-48.1%) was estimated for Anaplasma, which was the most frequently tested TBP in dromedaries, and DNA of Anaplasma marginale, Anaplasma centrale, Anaplasma ovis, Anaplasma platys, and A. platys-like were isolated, of which ruminants and dogs are reservoirs. Similarly, the estimated pooled prevalence for the two piroplasmid genera; Babesia and Theileria was approximately equal (10-12%) regardless of the detection method (microscopy or PCR testing). Nevertheless, Babesia caballi, Theileria equi, and Theileria annulata DNA have frequently been detected in camels but they have not yet been proven to be natural hosts. Scarce data detected Babesia microti, Anaplasma phagocytophilum, and Borrelia burgdorferi sensu lato (s.l.) DNA in blood of dromedaries, although ticks of the genus Ixodes are distributed in limited areas where dromedaries are raised. Interestingly, a pooled seroprevalence of 47.7% (26.3-69.2%) was estimated for Crimean-Congo hemorrhagic fever virus, and viral RNA was detected in dromedary blood; however, their contribution to maintain the viral transmission cycles requires further experimental investigation. The substantially low incidence and scarcity of data on Rickettsia and Ehrlichia species could imply that camels were accidentally infected. In contrast, camels may play a role in the spread of Coxiella burnetii, which is primarily transmitted through the inhalation of aerosols emitted by diseased animals and contaminated environments. Bactrian camels showed no symptoms due to the examined TBPs, meanwhile, clinical disease was seen in alpacas infected with A. phagocytophilum. Similar to dromedaries, accidental tick bites may be the cause of TBP DNA found in the blood of Bactrian camels.

Genetic diversity of Hyalomma marginatum in Tunisia is not influenced by the bio-climate

Ticks are important ectoparasites responsible for the transmission of several pathogens with significant medical, veterinary, and economic impacts. Climate and social changes have generated substantial changes in ticks' distribution, abundance, and activity patterns, including ticks belonging to the Hyalomma marginatum species. Knowledge on the genetic structure and dynamics of H. marginatum populations might contribute to a better understanding of their current and future evolution under the effects of anthropogenic factors and eco-climatic changes. In the present study, we investigated the genetic structure and phylogenetic distribution of H. marginatum across three bioclimatic regions in Tunisia using two mitochondrial markers (16S and 12S rRNA). The molecular investigations were based on 47 adult H. marginatum ticks collected from humid, upper semi-arid, and sub-humid regions of Tunisia. Our results revealed a genetic diversity of 0.278% and 0.809% using the 16S and 12S markers, respectively. The low genetic diversity that we observed raises the hypothesis of a bottleneck event occasioned by a reduction in the size of the tick population under the effects of environmental factors and/or human activities. This hypothesis is supported by the population's demographic history analysis, which revealed a clear deviation from neutrality and supports the occurrence of a bottleneck event followed by a demographic expansion. The fact that most 16S and 12S variability was present in the ticks from the humid bioclimatic zone may suggest that those ticks represent the ancestral population. Overall, the analysis has shown that the phylogenetic clusters do not correspond to the bioclimatic zones.

Crimean-Congo Hemorrhagic Fever Virus Seropositivity among Dromedary Camels, Algeria, 2020-2021

Serosurvey results for Crimean-Congo hemorrhagic fever virus antibodies in dromedary camels in Algeria indicate that the pathogen is circulating endemically in desertic areas, despite the hostile environment. Thus, dromedaries are suitable sentinels for detecting human risk for Crimean-Congo hemorrhagic fever in desertic areas.

Risk factors associated with Crimean-Congo hemorrhagic fever virus circulation among human, livestock and ticks in Mauritania through a one health retrospective study

BACKGROUND

Crimean Congo hemorrhagic fever (CCHF) is endemic in Southern Mauritania where recurrent outbreaks have been constantly observed since the 1980's. The present study is the first to assess CCHFV antibodies and RNA in humans.

METHODS

A retrospective study was conducted using 263 humans and 1380 domestic animals serum samples, and 282 tick specimens of Hyalomma genus collected from 54 settings in 12 provinces across Mauritania. Antibodies targeting CCHF viral nucleoprotein were detected in animal and human sera using double-antigen ELISA. CCHFV specific RNA was detected in human and animal sera as well as tick supernatants using a CCHFV real time RT-PCR kit. Individual characteristics of sampled hosts were collected at the same time and data were geo-referenced. Satellite data of several environmental and climatic factors, were downloaded from publicly available datasets, and combined with data on livestock mobility, animal and human density, road accessibility and individual characteristics to identify possible risk factors for CCHFV spatial distribution. To this end, multivariate logistic models were developed for each host category (human, small and large ruminants).

RESULTS

The overall CCHFV antibody prevalence was 11.8% [95% CI: 8.4-16.3] in humans (17.9% in 2020 and 5.4% in 2021; p = 0.0017) and 33.1% (95% CI: 30.1-36.3) in livestock. CCHFV-specific antibodies were detected in 91 (18.1%) out of 502 sheep, 43 (9.0%) out of 477 goats, 144 (90.5%) out of 161 dromedaries and 179 (74.6%) out of 240 cattle. CCHFV RNA was detected in only 2 (0.7%) sera out of 263 animals herders samples from Hodh El Gharbi province and in 32 (11.3%) out of 282 Hyalomma ticks. In humans as well as in animals, seropositivity was not associated with sex or age groups. The multivariate analysis determined the role of different environmental, climatic and anthropic factors in the spatial distribution of the disease with animal mobility and age being identified as risk factors.

CONCLUSION

Results of the present study demonstrate the potential risk of CCHF for human population in Mauritania primarily those living in rural areas in close vicinity with animals. Future studies should prioritize an integrative human and veterinary approach for better understanding and managing Crimean-Congo hemorrhagic fever.

Development and field evaluation of PCR assays based on minimum length Bm86 cDNA fragments required for Rhipicephalus and Hyalomma tick species delineation

Introduction

Hyalomma and Rhipicephalus ticks are important genera that can transmit diseases to both animals and humans, including Crimean-Congo hemorrhagic fever, tick-borne encephalitis, and several types of spotted fever. The accurate identification of tick species is essential for the effective control and prevention of tick-borne diseases. However, traditional identification methods based on morphology can be challenging and subjective, leading to errors. The development of DNA markers has provided more precise and efficient methods for tick species identification, but the currently available markers have limitations in their discriminatory power and sensitivity. To address this need for more sensitive and specific markers, this study aimed to identify two minimum sequence fragments required for tick Hyalomma and Rhipicephalus species identification using the Bm86 cDNA marker, which has previously been shown to be in perfect agreement with the current taxonomy of hard ticks based on its complete sequence.

Methods

Based on our in silico determination that a minimum sequence of 398 bp for Rhipicephalus spp. (from 1487 to 1884) and 559 bp for Hyalomma species (from 539 to 1097) was necessary for species delineation, two distinct PCR assays were developed to apply these sequences in practice.

Results and discussion

Discrimination between species within each genus was achieved through sequence homology and phylogenetic analysis following the sequencing of the two PCR products. Subsequently, their performance was evaluated by testing them on the field-collected ticks of the Hyalomma and Rhipicephalus genera obtained from various host animals in different geographic regions of Tunisia. The use of shorter partial sequences specific to the tick genera Rhipicephalus and Hyalomma, which target the tick's RNA banks, could represent a significant advance in the field of tick species identification, providing a sensitive and discriminatory tool for interspecific and intraspecific diversity analysis.

Human-biting ticks and zoonotic tick-borne pathogens in North Africa: diversity, distribution, and trans-Mediterranean public health challenges

North Africa is home to more than 200 million people living across five developing economies (Egypt, Libya, Tunisia, Algeria, and Morocco) and two Spanish exclaves (Ceuta and Melilla), many of whom are impacted by ticks and tick-borne zoonoses. Populations in Europe are also increasingly vulnerable to North African ticks and tick-borne zoonoses due to a combination of climate change and the movement of ticks across the Mediterranean on migratory birds, human travellers, and trafficked wildlife. The human-biting ticks and tick-borne zoonoses in North Africa are reviewed along with their distribution in the region. We also assess present and future challenges associated with ticks and tick-borne zoonoses in North African and highlight opportunities for collaboration and coordination between governments in Europe and North Africa to address public health challenges posed by North African ticks and tick-borne zoonoses.

Crimean–Congo hemorrhagic fever in the Arab world: A systematic review

Crimean-Congo hemorrhagic fever (CCHF) is an important tick-borne viral infection with a fatality rate of up to 50% during outbreaks. Crimean-Congo hemorrhagic fever virus (CCHFV) is sustained in the ecosystem in benign form through vertical and horizontal transmission cycles involving tick vectors, wildlife, and livestock. Hyalomma ticks are considered the major source of human infection. CCHF occurs most often among butchers, slaughterhouse workers, and farmworkers through infected tick bites or/and contact with blood and tissues of infected livestock. The nosocomial transmission can occur in auxiliary nurses and physicians through contact with the infected patients. The widespread distribution of CCHFV most probably occurred by ticks on migratory birds, or through international travel and trade of livestock and wildlife. During co-infections of ticks and vertebrates, reassortment among genome segments could play a significant role in generating diversity, and hence, a potential risk for the emergence of novel variants. In this systematic review, we aimed to determine the epidemiology, transmission, distribution, mortality, and clinical features of CCHF in 22 Arab countries, comprising the Arab world. Based on the analysis of 57 studies published from 1978 to 2021, we found 20 tick species that could be associated with CCHFV transmission. During the 43-year period, 321 cases of CCHF were reported from 9/22 Arab countries, Iraq, Kuwait, UAE, Saudi Arabia, Oman, Sudan, Egypt, Tunisia, and Mauritania. The mean case fatality rate was 29% during various outbreaks. Individuals working in abattoirs/slaughter houses, livestock farms, and healthcare were most at risk. Contact with blood or body secretions from infected animals and patients was the most common mode of transmission. A number of different animals, including cattle, goats, sheep, and camels were reported to be seropositive for CCHFV. The highest seroprevalence was observed in camels (29%), followed by cattle (21%), goats (15%), and sheep (14%). We discuss these results in the context of policy-making and potential preventative measures that can be implemented to reduce the burden of CCHF in the Arab world.

Serologic and molecular evidence for circulation of Crimean-Congo hemorrhagic fever virus in ticks and cattle in Bosnia and Herzegovina

Crimean-Congo haemorrhagic fever virus is a tick-borne zoonotic agent of the genus Orthonairovirus, and the causal agent of Crimean-Congo haemorrhagic fever in humans. The study is aimed at investigating the presence of CCHFV RNA in ticks and cattle in Bosnia and Herzegovina (B&H), as well as the exposure of cattle to CCHFV in this country. Only one pool of three male Hyalomma marginatum ticks tested positive for viral RNA (3/760, 0.39%). No viral RNA was detected in 206 bovine blood samples using real-time reverse-transcriptase PCR (RT-qPCR). The overall seroprevalence of CCHFV in the cattle population was estimated as 14.97% (72/481). The results indicate the presence and the established circulation of CCHFV in B&H. Considering the endemic character of CCHFV in the Balkans as well as our results, the possibility that CCHFV is endemic in the territory of Bosnia and Herzegovina is considered to be very high.

Crimean-Congo Hemorrhagic Fever Virus Past Infections Are Associated with Two Innate Immune Response Candidate Genes in Dromedaries

Dromedaries are an important livestock, used as beasts of burden and for meat and milk production. However, they can act as an intermediate source or vector for transmitting zoonotic viruses to humans, such as the Middle East respiratory syndrome coronavirus (MERS-CoV) or Crimean-Congo hemorrhagic fever virus (CCHFV). After several outbreaks of CCHFV in the Arabian Peninsula, recent studies have demonstrated that CCHFV is endemic in dromedaries and camel ticks in the United Arab Emirates (UAE). There is no apparent disease in dromedaries after the bite of infected ticks; in contrast, fever, myalgia, lymphadenopathy, and petechial hemorrhaging are common symptoms in humans, with a case fatality ratio of up to 40%. We used the in-solution hybridization capture of 100 annotated immune genes to genotype 121 dromedaries from the UAE tested for seropositivity to CCHFV. Through univariate linear regression analysis, we identified two candidate genes belonging to the innate immune system: FCAR and CLEC2B. These genes have important functions in the host defense against viral infections and in stimulating natural killer cells, respectively. This study opens doors for future research into immune defense mechanisms in an enzootic host against an important zoonotic disease.

Presence of antibodies to Crimean Congo haemorrhagic fever virus in sheep in Tunisia, North Africa

Crimean–Congo haemorrhagic fever (CCHF) is an emerging tick‐borne disease causing severe and fatal haemorrhagic syndrome in humans. Hyalomma spp. ticks are the primary vectors and sheep are important CCHF virus (CCHFV)‐amplifying hosts. In this study, blood samples and ticks collected in October 2019 from 270 sheep from 15 farms across Tunisia constituted the main research material. Moreover, the sera of the same animals taken at different periods between 2018 and 2019 were also used to obtain comparative results. To investigate the presence of anti‐CCHFV antibodies in sheep, all sera were tested using ELISA. Reactive sera were further characterised by a virus neutralisation test (VNT). Overall, one out of the 270 tested sheep was both ELISA‐ and strongly VNT‐positive to CCHFV. Another two sheep were borderline ELISA‐positive but did not exhibit neutralising antibodies. Ninety‐one ticks were collected from all sampled sheep, of which 34 (37.4%) belonged to Hyalomma spp. This is the first report of anti‐CCHFV antibodies in sheep from Tunisia. Both the results of this study and the recent CCHFV detection in ticks collected from camels in southern Tunisia indicate that further studies are needed to determine the competent tick vector in the country and to characterise the epidemiological cycle of CCHFV.

First Serological Evidence of Crimean-Congo Hemorrhagic Fever Virus and Rift Valley Fever Virus in Ruminants in Tunisia

Crimean-Congo hemorrhagic fever virus (CCHFV, Nairoviridae family) and Rift Valley fever virus (RVFV, Phenuiviridae family) are zoonotic vector-borne pathogens with clinical relevance worldwide. Our study aimed to determine seroprevalences of these viruses and potential risk factors among livestock (cattle, sheep, and goats) in Tunisia. Sera were tested for antibodies against CCHFV (n = 879) and RVFV (n = 699) using various enzyme-linked immunosorbent assays (ELISAs) and indirect immunofluorescence assays (IIFA). The overall seroprevalence of IgG antibodies was 8.6% (76/879) and 2.3% (16/699) against CCHFV and RVFV, respectively. For CCHF seropositivity bioclimatic zones and breed were potential risk factors for the three tested animal species; while the season was associated with cattle and sheep seropositivity, tick infestation was associated with cattle and goats seropositivity and age as a risk factor was only associated with cattle seropositivity. Age and season were significantly associated with RVFV seropositivity in sheep. Our results confirm the circulation of CCHFV and RVFV in Tunisia and identified the principal risk factors in ruminants. This knowledge could help to mitigate the risk of ruminant infections and subsequently also human infections.

Phenology and phylogeny of Hyalomma spp. ticks infesting one-humped camels (Camelus dromedarius) in the Tunisian Saharan bioclimatic zone

In this study, we report the results of a survey of Hyalomma ticks infesting one-humped camels in southern Tunisia. Examinations were conducted every second or third month on 406 camels in Tataouine district from April 2018 to October 2019. A total of 1902 ticks belonging to the genus Hyalomma were collected. The ticks were identified as adult H. impeltatum (41.1%; n = 782), H. dromedarii (32.9%; n = 626), H. excavatum (25.9%; n = 493), and H. marginatum for a single specimen. Although the camels were infested by ticks throughout the year, the highest overall infestation prevalence was observed in April 2018 (p < 0.01). The overall infestation intensity varied between 2.7 and 7.4 ticks/animal. There were no statistically significant differences in tick infestation prevalence based on age categories of the camels, and the overall infestation prevalence was between 82.7% and 97.4%. Female camels were significantly more infested with ticks (88.3%) than males (65.5%) (p < 0.01). The infestation prevalence of camels varied significantly according to the region where sampling took place (p < 0.01), but no correlations were found with abiotic factors. The preferred attachment sites for adult Hyalomma ticks were the sternum (38.3%; n = 729/1902), around the anus (36.2%; n = 689/1902), udder (18.4%; n = 350/1902), and inner thigh (6.9%; n = 132/1902). Morphological classification of ticks was corroborated by sequencing the cytochrome c oxidase I (Cox1) and 16S rDNA genes, and these sequences were also used to infer phylogenetic relationships. A single H. dromedarii seemed to be a natural hybrid with H. rufipes. More attention should be devoted by the veterinary services to the infestation of camels by ticks.