Research and analysis

HAIRS risk assessment: Crimean-Congo haemorrhagic fever

Updated 28 March 2024

About the Human Animal Infections and Risk Surveillance group

This document was prepared by the UK Health Security Agency (UKHSA) on behalf of the joint Human Animal Infections and Risk Surveillance (HAIRS) group.

HAIRS is a multi-agency cross-government horizon scanning and risk assessment group, which acts as a forum to identify and discuss infections with potential for interspecies transfer (particularly zoonotic infections). Its work cuts across several organisations, including:

• UKHSA

• Department for Environment, Food and Rural Affairs (Defra)

• Department of Health and Social Care (DHSC)

• Animal and Plant Health Agency (APHA)

• Food Standards Agency (FSA)

• Public Health Wales (PHW)

• Public Health Scotland (PHS)

• Department of Agriculture, Environment and Rural Affairs for Northern Ireland (DAERA)

• Welsh Government

• Scottish Government

• Public Health Agency of Northern Ireland

• Department of Agriculture, Food and the Marine, Republic of Ireland

• Health Service Executive, Republic of Ireland

• Infrastructure, Housing and Environment, Government of Jersey

• Isle of Man Government

• States Veterinary Officer, Bailiwick of Guernsey

Information on the risk assessment processes used by the HAIRS group can be found on GOV.UK.

Version control

Date of this assessment: March 2024

Date of initial risk assessments: V1.0 April 2017; V2.0 December 2018; V3.0 April 2021

Version: 4.0

Reason for the assessment: Updated to reflect the geographical expansion of CCHF virus (for example, detections in ticks in the south of France) and to incorporate the latest epidemiology and scientific literature.

Completed by: HAIRS members and external experts

Non-HAIRS members consulted:

• Dr. Kayleigh Hansford, UKHSA’s Medical Entomology and Zoonoses Ecology Team

• Dr. David Mesher, Lead Epidemiologist, UKHSA’s Emerging Infections and Zoonoses Team

• Dr. Sherine Thomas, Consultant in UKHSA’s Emerging Infections and Zoonoses Team

Summary

Crimean-Congo haemorrhagic fever (CCHF) is a tick-borne disease which cycles between a wide range of domestic and wild animals, with humans infected via tick bites or contact with infected blood and tissues. It is not present in the United Kingdom (UK), nor are there any identified established populations of Hyalomma ticks, the principal vectors of CCHF virus (CCHFV). However, there are multiple routes for the introduction of the tick into the UK, including through the movement of migratory birds.

In 2016, Spanish authorities reported the first autochthonous clinical cases of CCHF in Spain and in Western Europe, with a retrospective analyses identifying human cases dating back to 2013. Ticks in Spain had first been found to carry CCHFV in 2010, therefore the occurrence of CCHF human cases there was not unexpected. Since 2013, and as of February 2024, 12 human cases of CCHFV infection have been reported in Spain. Additionally, in October 2023, French officials reported the detection of CCHFV in Hyalomma marginatum ticks collected from cattle in the eastern Pyrénées. These were the first detections of CCHFV in ticks in France. 

In 2018, 2 Hyalomma tick species were detected in the UK. An adult male H. rufipes tick was detected in September 2018 on a horse with no history of travel. This suggests possible moulting for the first time of an imported H. rufipes nymph (via a migratory bird) to an adult, despite UK climate constraints previously considered to be a limiting factor for tick development. Additionally, an adult male H. marginatum tick (not feeding) was found on a human at a bird reserve in Norfolk in 2018. This is likely the result of a moulted nymph and the first evidence of H. marginatum moulting in the UK. This concurs with other reports in northern Europe during 2018 of Hyalomma ticks being found outside their endemic range during an unusually warm summer period. In July 2022, an adult male H. marginatium tick was found on a horse in the South-East of England, but this could not be confirmed as UK acquired.

As of February 2024, 2 travel associated human cases of CCHF have been reported in the UK. No locally acquired human cases have been reported to date, nor has CCHFV been found in any potential tick vector species found within the UK.

Assessment of the risk of infection in the UK:

Probability

Currently, the probability of infection is considered Very Low for the UK population.

Impact

The impact on the UK population is considered Very Low to Moderate.

Level of confidence in assessment of risk

Good. 

The quality of evidence used in this assessment is considered mostly good, and thus the confidence of the risk assessment output is good (high quality evidence from multiple reliable sources and verified, expert opinion concurs).

Actions and/or recommendations

Vector surveillance:

• continue close monitoring of the situation in Europe for further geographical expansion of CCHF tick vector species 

• continue monitoring for new evidence as to the presence of Hyalomma species in the UK through existing UK tick surveillance schemes

• consider broader surveillance for Hyalomma species, including targeted tick surveillance through occupational groups (for example, equine veterinary professionals)

• raise professional and public awareness to tick surveillance schemes within the UK

• upon detection of Hyalomma ticks in the UK, ensure data is shared between agencies and HAIRS is informed for joint monitoring and interpretation

• ensure all submissions of Hyalomma ticks to tick surveillance schemes are followed up by agencies to assess whether they are locally acquired, or travel associated

• Hyalomma ticks identified in the UK should be tested for CCHFV

• consider inter stakeholder contingency planning for invasive tick species, such as controlling tick infestations on animals or in stables and barns

For animal health professionals:

• ticks identified on animals should be submitted to tick surveillance schemes

• raise awareness with animal keepers of potential for tick establishment where animals and birds co-exist (for example, in stables)

For public health professionals:

• continue to monitor the situation in European countries for increasing reports of autochthonous cases or changes in pathogenicity for human infections

• raise awareness on tick avoidance measures for the public, particularly travellers to known affected areas

• clinicians should be made aware of the clinical features of CCHF and consider it early in travellers with suspect symptoms who have visited endemic areas and taken part in higher risk activities (for example, outdoor activities, animal slaughter)

• ensure appropriate clinical assessment and public health management protocols are available to manage a human case of CCHF in the UK

Step 1. Assessment of the probability of infection in the UK human population

This section of the assessment examines the likelihood of an infectious threat causing infection in the UK human population. Where a new agent is identified there may be insufficient information to carry out a risk assessment and this should be clearly documented. Please read in conjunction with the Probability algorithm.

Is this a recognised human disease?

Outcome

Yes.

Quality of evidence

Good.

CCHF was first described in the Crimea in 1944, where an outbreak of an acute febrile illness with a high incidence of shock and bleeding occurred among soldiers and agricultural workers. In 1969, it was recognised that the virus causing this disease was identical to a virus that had been isolated from a child in the Congo in 1956 (1). Humans (and possibly non-human primates (2) are the only animal species known to manifest severe clinical CCHF disease (3, 4).

CCHF virus (CCHFV) is a member of the family Nairoviridae, in the genus Orthonairovirus (5). CCHFV exhibits great sequence diversity. From analysis of its S, L and M segments, phylogenetic trees have been constructed containing lineages I to VI. CCHFV is thought to have originated in Africa between 1,000 and 5,000 years ago, although a strain (Ap92) found in Greece is considered an ancient lineage. The virus was introduced to Central and South Asia in the Middle Ages, with spread into Europe considered a more recent event, likely via a single introduction into central Russia. Westward spread has since taken place, with further geographical expansion considered likely (6, 7).

CCHF has a widespread geographical distribution. It is considered endemic in countries in Africa, the Balkans, the Middle East, western and south-central Asia. It is estimated that globally between 10,000 and 15,000 human infections, including approximately 500 fatalities, occur annually (8). The distribution of human cases corresponds to the geographical range of established Hyalomma tick species (3), notably H. marginatum and H. lusitanicum, which are considered the primary vectors of CCHFV (4).

Globally, there have been case reports, virological or serological evidence of human infection in at least 55 countries (3, 9). In the European Region and its neighbouring countries, locally acquired human cases and/or outbreaks have been reported from Albania, Bulgaria, Georgia, Greece, Kosovo, Russia, Spain, Turkey and Ukraine (8, 10). Spain officially reported its first autochthonous case in August 2016, the first in Western Europe, following their first detection of CCHFV infected ticks in 2010 (11 to 13). However, retrospective analyses identified human cases in western Spain dating back to summer 2013 (14). As of January 2024, a total of 12 confirmed cases have been officially reported from Spain, including one case of nosocomial transmission in 2016, and 4 fatalities (one each in 2016, 2018, 2020 and 2022) (10). A CCHFV seroprevalence study carried out between 2017 and 2018 in Castile-León, a Spanish region where CCHF cases had been reported, found evidence of past exposure to CCHFV of between 0.58% and 1.16% in healthy blood donors (results varied dependent on assay used) (15). CCHFV genotypes Africa III and Europe V have been detected both in human cases (16) and in different tick species (H. lusitanicum and Dermacentor marginatus) collected from various wild ungulate hosts (red and fallow deer; Eurasian wild boar) across south-west Spain (17), showing the wide spatial presence of CCHFV in this region. Authorities state there is a moderate likelihood of future cases in known CCHF risk areas, although the impact would be low given the expected small number of cases and availability of adequate means of isolation and control of cases (18).

At the end of October 2023, French officials reported the detection of CCHFV in H. marginatum ticks collected from cattle in the eastern Pyrénées as part of an active surveillance project on equestrian and cattle premises in the region (19). Whilst H. marginatum have established populations in southern France, this was the first time the presence of the virus in tick populations had been confirmed in the country. This geographical expansion of CCHFV is consistent with model predictions by Messina and Wint (20), who concluded that environmental suitability for the disease likely extends as far as north-west France and central Europe, compared to 2015 model predictions (20, 21). As of January 2024, no autochthonous human cases have ever been reported in France.

CCHF disease has varying manifestations from asymptomatic or subclinical infection through to fulminant haemorrhage. The incubation period is usually less than 14 days (typically 3-7 days), although this duration varies depending on factors including viral dose and route of exposure; it is often shorter following nosocomial infection (8). The onset of symptoms is sudden, with fever, severe headache, dizziness, photophobia, malaise, myalgia and back pain reported. Sore throat, nausea, vomiting and diarrhoea may also feature. Hepatomegaly and lassitude can develop after 2 to 4 days (1, 22, 23). The haemorrhagic forms of the disease are more diverse than other viral haemorrhagic fevers, starting with a petechial rash, which usually appears in the first week of illness and progressing through extensive bruising and bleeding under the skin, to excessive bleeding in the second week of illness in those with severe infection (23). Cerebral haemorrhage has also been described (24). In fatal cases, death occurs from haemorrhage, multi-organ failure and shock usually between days 5 and 14 of illness (1). Reported overall case fatality rates have varied from 5% to more than 40%, though this disparity is likely skewed by small sample sizes and failure to detect and report less severe cases (1). It is possible that subclinical infections represent a substantial proportion of cases; thus resulting in under ascertainment of the true number of cases (4).

CCHFV is maintained in several ixodid (hard) tick species and these are responsible for spreading the virus to a wide range of wild and domestic animals. Illness has not been reported in these mammals, but there is evidence of transient viraemia for up to 15 days (25). Some mammals, and probably some avian species, act as amplifying hosts that can subsequently infect ticks feeding on them (1, 26). Human disease from an animal source can occur following exposure to blood and/or body fluids of infected animals (particularly livestock) and via the bite of an infected tick (22). In areas where CCHFV is known to circulate, a higher exposure risk may therefore exist for people participating in outdoor activities (for example farmers, game hunters, forestry workers and hikers) and those who have prolonged direct exposure to livestock and animal products (for example shepherds, farmers, butchers, slaughterhouse workers and veterinarians) (4).

Contaminated meat is generally not considered a potential source of exposure to CCHFV, as post-slaughter acidification will normally inactivate virus present (8). There have, however, been reported human cases of infection following the consumption of raw meat and liver (27) from freshly slaughtered infected animals. Pre-slaughter stress in animals can reduce the extent of post-slaughter acidification. Whether the virus can be transmitted via milk is uncertain (28), but unpasteurised milk has been suggested as a possible route of exposure (29). 

While CCHFV has been detected in many tick species, only some ticks have been confirmed as competent vectors (30). Ticks of the genus Hyalomma are the principal source of human infection and the key Hyalomma vectors involved vary geographically (1). Some species of the genus Dermacentor and Rhipicephalus have also been shown to be capable of transmitting CCHFV (26), but their role in maintaining active foci is debated (31). In Spain, CCHFV has been detected in H. lusitanicum, H. marginatum, and D. marginatus (17, 32).

Infection within generations of key Hyalomma vectors is maintained by transstadial (between stages) and transovarial transmissions (in other words, by vertical transmission). The virus can be maintained for extended periods via these routes, even in the absence of susceptible vertebrate hosts (26).  

Is the disease endemic in humans within the UK?

Outcome

No.

Quality of evidence

Good.

Travel associated human CCHF cases have very rarely been confirmed in the UK. Only 2 laboratory-confirmed clinical cases have been diagnosed; one imported from Afghanistan in 2012 (33) and the other from Bulgaria in 2014 (34). No onward transmission resulted from either case.

Is the disease endemic in animals within the UK?

Outcome

No.

Quality of evidence

Good.

The virus has not been found in UK mammals. Relevant tick species have been detected in the UK; there have been 2 reports of UK acquired Hyalomma ticks on hosts without a history of travel (35, 36), and occasional reports of importations via migratory birds (37) or imported animals (38). A distribution map for H. marginatum in Europe is shown below (Figure 1).

Figure 1. The known distribution of Hyalomma marginatium and Hyalomma lusitanicum in Europe and its neighbouring countries, as of October 2023. Source: European Centre for Disease Prevention and Control. Accessed: 22 January 2024

Historical tick records from the UK (39) have demonstrated that importations of H. marginatum have occurred via migratory birds, although a study in 2004 (40) collected 38 ticks from more than 10,000 birds examined, and none were Hyalomma. A subsequent UK study carried out in the spring of 2010 and 2011 examined 971 migratory birds of 29 species (30). From 53 infested birds of 9 species, 68 ticks were recovered. These were mostly Ixodes species (54/68, 79%), but 21% (14/68) were H. marginatum. The H. marginatum were found on 4 species of bird and all ticks were negative for CCHFV by PCR (30). As of January 2024, 15 Hyalomma ticks have been received by UKHSA’s passive Tick Surveillance Scheme (TSS) (Table 1).

Table 1. Hyalomma ticks received by UKHSA’s passive Tick Surveillance Scheme (TSS), as of January 2024.

Tick species	Year	Host species	reference
H. marginatum	2009	Horse	(41)
H. lusitanicum	2016	Dog	(38)
H. lusitanicum	2017	Human	TSS data
H. truncatum	2017	Human	TSS data
H. lusitanicum	2018	Dog	TSS data
H. rufipes	2018	Horse	(36)
H. marginatum	2018	Human	(35)
H. lusitanicum	2019	Human	TSS data
H. lusitanicum	2019	Human	TSS data
H. aegypticum	2019	Human	TSS data
H. aegypticum	2020	Human	TSS data
H. lusitanicum	2022	Human	TSS data
H. marginatum	2022	Horse	TSS data
H. excavatum	2023	Human	TSS data
H. aegypticum	2023	Human	TSS data

All but the H. rufipes (on a horse) and the H. marginatum (on a human) were linked to overseas travel to Hyalomma-endemic regions. The H. marginatum found on a horse in 2022 may have been acquired in the UK, but this was not confirmed. The detection of an adult male H. rufipes tick on a horse in Dorset and an adult male H. marginatum tick on a human in Norfolk, both with no history of travel, were possibly the result of importation of a nymph on a migratory bird, and subsequent moulting to an adult during the unusually warm summer of 2018 (35, 36). CCHFV was not detected in either tick (or the 2 ticks imported on dogs).

To date there is no evidence that any imported Hyalomma ticks have led to established populations in the UK.

Are there routes of introduction into animals in the UK?

Outcome

Yes.

Quality of evidence

Satisfactory.

There are routes of introduction of CCHFV into the UK via tick infested bird migration and animal movements. The latter route does not appear to have been commonly documented (25), although in the UK, Hyalomma tick species have been detected on an imported horse (41), 2 travelling dogs (38) and humans (TSS data) (Table 1).

In 2021, Fanelli and Buonavogilia assessed the likelihood of entry of CCHFV (through infected tick vectors, wildlife and livestock movements) into 9 CCHF-free countries in Southern and Western Europe (Austria, Belgium, France, Germany, Italy, Luxembourg, Netherlands, Slovenia and Switzerland). The likelihood of CCHFV entry was assessed as low to medium for most countries, with the exception of France, where the risk was considered high (42).

Livestock were, until January 2021, traded between European Union (EU) member states and the UK on an Intra Trade Animal Health Certificate (ITAHC), which has no specific requirements for CCHF freedom and no testing or tick treatment requirements. Horses were moved – until January 2021 – using either an ITAHC, or an owner health attestation, or on a commercial document for registered horses. Importation from outside the EU is strictly controlled, with few countries approved for trade in live ruminant livestock (206/2010/EU) and few approved bodies for trade in exotic ruminants. None of the approved third countries have endemic CCHF. Horses can, however, enter the UK from many third countries – including the Middle East and North Africa – and from January 2021 this includes the EU, and there are no tick treatment requirements on the Export Health Certificate. Nevertheless, since 2022, a vector borne disease of ruminants, Epizootic Haemorrhagic Disease, has been detected in Spain and France, and there is a bluetongue (BTV-3) epizootic in the Netherlands, Belgium and Germany, which means there are no imports of cattle or deer or small ruminants from these regions.

Jameson and others estimated that there could be tens of thousands of H. marginatum being imported into the UK annually via birds migrating from Africa (30). However, no established populations are known to have resulted from importation of this nature. Additionally, it has previously been considered that there is a climatic limitation with the UK being too wet or too cold during the summer potentially preventing Hyalomma development from nymph to adult. However, during periods with increased summer temperatures such as those experienced during 2018 (43), nymphal moulting may take place in the UK, as suggested by the 2018 detections of a male H. rufipes on an horse in Dorset and a male H. marginatum on a human in Norfolk; both with no history of travel. CCHFV was not detected in either tick (35, 36). However, model predictions by Gillingham and others suggest that whilst future autumn temperatures will increase in the UK, they are likely to remain below the threshold required for Hyalomma marginatum populations to become established (37).

Gale and others modelled the absolute risk of CCHFV infections of livestock through immature ticks via migratory birds as being very low (44). An assessment of the risk that ticks on northward migrating birds present to Great Britain was conducted in Spain and examined 564 birds. Overall, 65 Hyalomma tick species individuals were found on 26 birds (2.2%), none of which were positive for CCHFV (45). Tick infestation rates on birds entering the UK is estimated at <1%, and such migratory birds are considered more likely to have originated in north Africa or southern Europe. The conclusion was that migratory birds present an extremely low but not negligible risk of CCHFV being introduced into Great Britain.

Hyalomma lusitanicum has been imported into the UK on 6 occasions (2016 to 2023) on dogs and humans, each with a recent history of travel to Portugal, Spain, Menorca or Malta (38) (TSS data). These importations are considered likely to be rare events. The role of this tick species in transmission of CCHFV is unclear, though it was found to harbour CCHFV in Spain (11).

Rodents and lagomorphs are also imported into the UK, mostly as pets or for the pet trade; again, there are no requirements for tick treatment and no reports of Hyalomma tick infestations. While the host preferences for Hyalomma ticks are generally considered to be rodents, lagomorphs and avian species (46), other hosts are possible, if rare. For example, Spur-thighed tortoises (Testudo graeca) imported into the UK were found to be infested with H. aegyptium (47), a species known to be infected with CCHFV in Turkey and Syria; however, this tick species is not known to be associated with virus transmission. A large variety of reptiles are imported into the UK for the pet trade and there are no requirements for health certification or tick treatment. 

Although only 2 CCHF travel-associated human cases have been reported in the UK to date, it is possible additional travel associated cases have gone undetected due to the asymptomatic or mild nature of some disease manifestations.   

Are effective control measures in place to mitigate against these routes of vector introduction?

Outcome

No.

Quality of evidence

Satisfactory.

Effective control of introduction is not possible due to the role of migratory birds. There are no statutory controls for ticks on imported livestock or other hoof-stock. There are no tick controls in the Pet Travel Scheme passport or for commercial pets. Tick treatment in pets is voluntary, but it is recommended to all pet owners by the British Small Animal Veterinary Association whether their cat or dog is travelling or not (49). There are no controls for wild birds.

The presence of a viraemia due to CCHFV in an animal species would most likely be silent, thus importation of infected animals could pass any veterinary pre-movement inspection. However, there are controls on trading of livestock animals within and between EU member states and on importation from outside the EU, relating to the disease-free status of the establishment and the region, albeit not specifically related to CCHF. Importation from many CCHFV-endemic countries is not allowed, due to EU legislative requirements, based on the status of other more important livestock diseases in the country. 

Do environmental conditions in the UK support the natural vectors of disease?

Outcome

Predominantly no, with current climate in the UK being considered too wet and cold for nymph survival. However, during unusually warm summers (as observed in 2018), conditions may facilitate nymph survival and moulting.

Quality of evidence

Satisfactory.

There have been no established Hyalomma tick populations detected in the UK, despite presumed frequent incursions via migratory birds. This is considered to be likely due to a climatic limitation, with the UK being too wet or too cold during the summer for Hyalomma development (26), and too cold during autumn to facilitate nymph survival (37).The recent detections of locally acquired Hyalomma ticks with no history of travel suggests that increased summer temperatures may support nymphal moulting in the UK following introduction via migratory birds. However, the lack of establishment of this tick in other parts of Europe with similar climatic conditions (see Figure 1) suggests that survival in the UK may be restricted. Model predictions by Gillingham and others suggest that whilst future autumn temperatures will increase in the UK, they are likely to remain below the threshold required for Hyalomma marginatum populations to become established (37).

Will there be human exposure?

Outcome

No, not currently

Quality of evidence

Good.

There is no evidence to suggest CCHFV is present in the UK and, to date, only a limited number of imported Hyalomma species have been detected, with no indication of establishment.

Future vector incursions and travel-associated human infections should not be unexpected, particularly as the geographical distribution of CCHFV expands (for example, into areas frequented by UK travellers including Spain and France). The possibility of human-to-human transmission following a sporadic imported human case into the UK is plausible.

Outcome of probability assessment

The probability of human infection with CCHF in the UK population is considered very low.

Step 2: Assessment of the impact on human health

The scale of harm caused by the infectious threat in terms of morbidity and mortality depends on spread, severity, availability of interventions and context. Please read in conjunction with the Impact algorithm.

Is there human-to-human spread of this pathogen?

Outcome

Yes, however the predominant route of transmission is via the bite of an infected tick

Quality of evidence

Good.

The most common route of acquisition of CCHF is tick-borne or via direct contact with blood or tissues of an infected animal during and immediately after slaughter (22). However, person-to-person transmission can occur via contact with the blood and/or body fluids of infected persons (1). Nosocomial transmission is known to occur and has been well-documented in many countries (49), including in Spain in 2017 (50) and North Macedonia in 2023 (51), but has not occurred in the UK.

Possible sexual transmission and vertical transmission have also been described (52 to 54).

Is there zoonotic or vector-borne spread of this pathogen?

Outcome

Yes.

Quality of evidence

Good.

CCHF is primarily a tick-borne infection, but disease may also be acquired via contact with the blood and/or body fluids of infected animal or human cases (1). There have also been reported human cases of infection following the consumption of raw meat and liver from freshly slaughtered infected animals (27).

For zoonoses or vector-borne disease, is the animal host or vector present in the UK?

Outcome

Yes, animal hosts are present in the UK. However, there are no established Hyalomma tick populations in the UK.

Quality of evidence

Good.

The virus is not found in UK animals and there are no established Hyalomma tick populations in the UK. However, CCHFV has a broad host range, including livestock animals, which are present in the UK.

The incidents of locally acquired adult Hyalomma ticks during 2018, on a human and a horse with no history of travel, suggest moulting of nymphs has taken place in the UK in these instances, potentially associated with the unusually warm summer of 2018 (43). Winter temperatures in the UK may not be a limiting factor for continued survival of adults, which could therefore result in questing of adult Hyalomma next spring. It is possible that future human exposure to Hyalomma ticks in the UK could occur following warm summers permissive for nymphal moulting following importation of ticks.

Is the UK human population susceptible?

Outcome

Yes.

Quality of evidence

Good.

There is no reason to suspect that the UK population is any different in susceptibility to CCHFV than populations in endemic countries. Two UK travellers to date have acquired confirmed clinical CCHF overseas, as have a number of other tourists from other countries; more than 20 travel-related cases have been documented in the literature (55, 56).

Does it cause severe disease in humans?

Outcome

Yes.

Quality of evidence

Good.

Although asymptomatic infection occurs, it is not clear what proportion of infections lead to overt clinical disease. However, when it occurs, CCHF can be a severe illness with a high mortality. In endemic countries, the case fatality rate is variable, ranging from 5% to more than 40% (1). In a series of travel-related infections, 12 out of 21 cases (57%) had a fatal outcome (55).

Would a significant number of people be affected?

Outcome

No.

Quality of evidence

Satisfactory.

The burden of disease due to CCHFV even in endemic countries appears to be comparatively low, although there is great variation in surveillance, detection and reporting.

In the UK, it is unlikely that a significant number of cases would occur from environmental exposures. There are robust and tested procedures for managing and caring for patients with viral haemorrhagic fevers (57). However, it is possible that delayed diagnoses in healthcare settings could have substantial operational impacts if staff exposed to a case between the time of admission and confirmation of infection are required to isolate as part of public health follow-up. There has been no transmission to healthcare workers involved in the care of patients with any viral haemorrhagic fever in the UK. However, nosocomial transmission has been documented in other countries (58), highlighting the importance of CCHF awareness amongst healthcare professionals to ensure rapid diagnoses and the implementation of effective infection prevention and control in healthcare settings.

Are effective interventions available?

Outcome

Yes. Whilst non-pharmaceutical interventions are available, there are no specific licensed vaccines or antivirals to treat CCHF.

Quality of evidence

Satisfactory.

Preventive measures in endemic countries focus on education around tick avoidance (59), treatment of livestock to control tick infestations, minimising contact with blood and/or body fluids of livestock animals (55) and infection prevention and control measures in healthcare settings (49).

There are no licensed vaccines or specific antivirals to treat CCHF. In recent years, a better understanding of the function of CCHFV proteins in viral replication and improved animal models have provided important insights into CCHFV pathogenesis, thus enabling preclinical testing of multiple vaccine platforms and therapeutic strategies for CCHF (60). However, this is still an area of development. The use of the antiviral ribavirin for treatment may be beneficial, provided it is commenced early in the course of illness (1) but recently the evidence for this has been increasingly challenged and more work is needed to find the best treatment regimen. Ribavirin has also been suggested as post-exposure prophylaxis following percutaneous exposure (61). Favipiravir showed good activity in treating bunyavirus infections in laboratory animals, but currently there are no data available on its efficacy in humans (62).

Treatment of a case in the UK would be supportive and include symptom relief, replacing blood components, balancing fluids and electrolytes and maintaining oxygen status and blood pressure (57, 63).

Intensive public messaging about preventive measures would take place in response to the first detection of established populations of Hyalomma ticks in the UK, the first detection of CCHFV in a tick in the UK and the first detection of a locally acquired human case.

Outcome of impact assessment

The impact of CCHF on human health in the UK is considered very low to moderate.  

Annexe A. Assessment of the probability of infection in the UK population algorithm

Annexe B. Assessment of the probability of infection in the UK population algorithm: accessible text version

Outcomes are specified with (Outcome) beside the appropriate answer.

Question 1: Is this a recognised human disease?

Yes

Go to question 3. (Outcome)

No

Go to question 2.

Question 2: Is this a zoonosis or is there a zoonotic potential?

Yes

Go to question 4.

No

The probability of infection in the UK population is considered very low.

Question 3: Is this disease endemic in humans within the UK?

Yes*

Go to question 5.

No

Go to question 4. (Outcome)

*This pathway considers reverse-zoonosis of a pathogen already in circulation in the human population.

Question 4: Is this disease endemic in animals in the UK?

Yes

Go to question 8.

No

Go to question 5. (Outcome)

Question 5: Are there routes of introduction into animals in the UK?

Yes

Go to question 6. (Outcome)

No

The probability of infection in the UK population is considered very low.

Question 6: Are effective measures in place to mitigate against these?

Yes

The probability of infection in the UK population is considered very low.

No

Go to question 7. (Outcome)

Question 7: Do environmental conditions in the UK support the natural vectors of disease?

Yes

Go to question 8. (Outcome)

No

The probability of infection in the UK population is considered very low. (Outcome)

Question 8: Will there be human exposure?

Yes

Go to question 9.

No

The probability of infection in the general UK population is considered very low. (Outcome)

Question 9: Are humans highly susceptible?**

Yes

Go to question 10.

No

The probability of infection in the UK population is considered low.

**Includes susceptibility to animal-derived variants

Question 10: Is the disease highly infectious in humans?

Yes

The probability of infection in the UK population is considered high.

No

The probability of infection in the UK population is considered moderate.

Annexe C. Assessment of the impact on human health algorithm

Annexe D. Assessment of the impact on human health algorithm: accessible text version

Outcomes are specified by (Outcome) beside the appropriate answer.

Question 1: Is there human-to-human spread?

Yes

Go to question 4. (Outcome)

No

Go to question 2. (Outcome)

Question 2: Is there zoonotic or vector-borne spread?

Yes

Go to question 3. (Outcome)

No

The impact of infection in the UK population is considered very low.

Question 3: For zoonoses or vector-borne disease, is the animal host or vector present in the UK?

Yes

Go to question 4. (Outcome)

No

The impact of infection in the UK population is considered very low. (Outcome)

Question 4: Is the human population susceptible?

Yes

Go to question 5. (Outcome)

No

The impact of infection in the UK population is considered very low.

Question 5: Does it cause severe disease in humans?

Yes

Go to question 8. (Outcome)

No

Go to question 6.

Question 6: Is it highly infectious to humans?

Yes

Go to question 9.

No

Go to question 7.

Question 7: Are effective interventions available?

Yes

The impact of infection in the general UK population is considered very low.

No

The impact of infection in the general UK population is considered low.

Question 8: Would a significant* number of people be affected?

Yes

Go to question 10.

No

Go to question 9. (Outcome)

*This question has been added to differentiate between those infections causing severe disease in a handful of people and those causing severe disease in larger numbers of people. ‘Significant’ is not quantified in the algorithm but has been left open for discussion and definition within the context of the risk being assessed.

Question 9: Are effective interventions available?

Yes

The impact of infection in higher-risk groups is considered low. (Outcome)

No

The impact of infection in higher-risk groups is considered moderate. (Outcome)

Question 10: Is it highly infectious to humans?

Yes

Go to question 12.

No

Go to question 11.

Question 11: Are effective interventions available?

Yes

The impact of infection in the UK population is considered moderate.

No

The impact of infection in the UK population is considered high.

Question 12: Are effective interventions available?

Yes

The impact of infection in the UK population is considered high.

No

The impact of infection in the UK population is considered very high.

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