CCHF is endemic in certain countries (Africa, Asia, Middle East) and is also prevalent in some eastern and southern European countries, notably Spain. CCHF virus was first detected in France in ticks collected from cattle farms in the south of the country in 2023, and no indigenous human cases have been reported to date.
What are the causes of the disease?
It is caused by a single-stranded RNA virus. Belonging to the Nairoviridae family, the virus is spherical in shape, with a diameter ranging from 80 to 120 nm. While infection with the CCHF virus typically causes relatively mild symptoms, the disease can progress to become severe, with multiple hemorrhages and organ failure resulting in death.
What are the symptoms?
The incubation period of the virus will depend on the mode of infection (tick bite or contact with infected blood or tissue). It varies from 3 to 7 days on average.
Symptoms are typically mild and flu-like: fever, muscle aches, rigors and dizziness. Nausea, vomiting, sore throat, abdominal pain and mood swings may occur. After 2 to 4 days, symptoms of depression or fatigue may appear.
When the disease runs an unfavorable course, it can cause hemorrhage and a rapid deterioration in renal and hepatic function. In this severe form of the disease, the mortality rate is between 5% and 30%, and most patients die during the second week of illness.
For those who recover, improvement is usually seen 9 to 10 days after the onset of symptoms.
While humans can develop severe forms of the disease, the infection is almost exclusively asymptomatic in other vertebrates.
How does the disease spread?
The CCHF virus is transmitted mainly through bites of ticks of the genus Hyalomma. In mainland France, where its presence has been confirmed since 2015, Hyalomma marginatum – the vector of the virus – is being monitored particularly closely. It is a relatively large tick (5 to 8 mm) with a long rostrum (pointed projection) and bicolored legs. It tends to bites humans, in particular during its period of activity between March and July.
Hyalomma marginatum's need for a warm, dry climate explains why the presence of this tick species in France is currently limited to the departments bordering the Mediterranean, Ardèche and Drôme. However, with global warming, Hyalomma marginatum's range is likely to expand across mainland France in the coming years.
In addition to tick bites, the CCHF virus can also be transmitted by contact with the blood or fluids of contaminated humans or animals. Although the vast majority of non-human animals are asymptomatic, they nonetheless carry enough virus in their bodies to cause further infections for around one week.
The disease is not airborne, nor is it transmitted by ingesting raw milk dairy products.
How is infection diagnosed?
Clinical diagnosis of the disease is difficult, as the initial symptoms are non-specific.
Infection with Crimean-Congo hemorrhagic fever virus can be confirmed by a number of different methods. The main ones are:
- detection of the viral genome by RT-PCR
- detection of a viral antigen or characteristic antibody with immunological tests
- isolation of the virus in cell culture
What treatments are available?
Management of the disease is mainly symptomatic.
An antiviral drug, ribavirin, has been suggested as a treatment for patients at the onset of symptoms, but its efficacy is still unclear.
There is no vaccine against CCHF.
How can the disease be prevented?
The mainstay of CCHF prevention is personal protection against tick bites. The best way to avoid ticks is to wear closed shoes and clothing that covers the body and is light in color (making it easier to spot a tick) when walking in the open country, keep to marked paths, use insect repellents if necessary, and perform a check after a walk in the woods (especially the armpits, knee folds, scalp, etc.).
Healthcare and slaughterhouse workers, veterinarians and livestock farmers must wear appropriate protective clothing and equipment (goggles, gloves, etc.) to avoid contact with the bodily fluids of potentially infected humans or animals.
Who is affected?
CCHF is endemic to Africa, Asia and the Middle East. The virus is also prevalent in some eastern and southern European countries.
The CCHF virus was detected for the first time in France in 2023 in some 100 ticks collected from cattle farms in the south of the country. As of October 2023, no indigenous cases have been detected in humans in France.
In Spain, a dozen human cases have been reported since 2016, at a rate of one to three per year.
Farmers, slaughterhouse workers and veterinarians who come into contact with blood or tissue from possibly infected animals are at greater risk of infection.
Find out more about Crimean-Congo hemorrhagic fever on the WHO website.
November 2023