Background information

Crimean-Congo haemorrhagic fever (CCHF) is a viral haemorrhagic fever caused by a virus of the Nairovirus group. CCHF is a zoonosis, and infects a range of domestic and wild animals. It is spread via the bite of an infected tick. CCHF was first described in the Crimea in 1944, among soldiers and agricultural workers, and in 1969 it was recognised that the virus causing the disease was identical to a virus isolated from a child in the Congo in 1956.

Epidemiology

CCHF virus is endemic in many countries in Africa, the Middle East, Eastern Europe and Asia, and outbreaks have been recorded in Russia, Turkey, Iran, Kazakhstan, Mauritania, Kosovo, Albania, Pakistan, and southern Africa in recent years. The first clinical case of CCHF was reported in Greece in July 2008. The global distribution of cases corresponds to those areas where the ticks are found.

The virus is spread by the bite of infected Ixodid ticks, and the most efficient and common vectors appear to be members of the Hyalomma genus, which commonly infest livestock and other animals. Immature ticks acquire the virus by feeding on infected small animals. Once infected, the tick carries the virus for life, and passes it to animals or humans when it bites them. Domestic ruminants such as cattle, sheep and goats carry the virus for around one week after becoming infected. Most birds are thought to be relatively resistant to infection with CCHF virus, however, many bird species carry Hyalomma ticks, and human cases have occurred in those working with ostriches in the past.

Transmission

Humans may be infected with CCHF by the bite of an infected tick, contamination with tick body contents, or direct contact with the blood, tissues or body fluids of infected humans or animals. The majority of cases occur in those living in tick infested areas with occupational exposure to livestock, including farmers, veterinarians, slaughter-house workers, livestock owners and others working with animals. Cases also occur in healthcare workers or others caring for infected persons without taking adequate infection control precautions.

Diagram of transmission cycles

CCHF outbreaks are generally associated with a change in situation such as war, population and animal movements, or climatic and vegetation changes which produce more ground cover for small mammals which act as hosts for ticks. These conditions can lead to explosions in tick populations, and allow increased tick/human contact.

The disease

The incubation period of CCHF appears to vary according to the mode of acquisition of the virus. If a patient has been infected by a tick bite, the incubation period is usually 1-3 days, and up to 9 days. Infection via contact with infected blood or tissues leads to an incubation period of 5-6 days, and the maximum recorded incubation period is 13 days. The illness begins abruptly, with fever, muscle aches, dizziness, neck pain and stiffness, backache, headache, sore eyes and photophobia (sensitivity to light). Nausea, vomiting and sore throat may also occur, with diarrhoea and abdominal pain. Over the next few days the patient may experience mood swings, confusion and aggression, followed by sleepiness, depression and liver enlargement. More severe symptoms may follow, including petechial rash (a rash caused by bleeding into the skin), bruising and generalised bleeding of the gums and orifices. In severe cases patients develop failure of the liver, kidneys and lungs, and become drowsy and comatose after 5 days. Approximately 30% of cases are fatal.

Diagnosis

Diagnosis of CCHF requires highly specialised, high biosafety level laboratory facilities. Antibodies may be detected in serum by about day 6 of illness. The virus may be isolated from blood or tissue specimens in the first 5 days of illness, and grown in cell culture, and nucleic acid detection methods may also be used to detect the viral genome. Patients with fatal disease do not usually develop a detectable antibody response, and in these individuals, and those in the early stages of infection, diagnosis is by virus detection.

Treatment

General supportive therapy is given, including replacement of blood components, balancing fluids and electrolytes, and maintaining oxygen status and blood pressure. There is evidence that CCHF responds to treatment with the antiviral drug ribavirin, in both oral and intravenous formulations.

Prevention and control

Persons living in or visiting endemic areas should use personal protective measures to avoid contact with ticks. This includes avoiding areas where ticks are abundant at times when they are active, using tick repellents, and carefully checking clothing and skin for ticks.

Those who work with livestock or other animals in endemic areas should protect themselves by using tick repellents on their skin and clothing, and wearing gloves or other protective clothing to prevent skin coming into contact with infected tissue or blood.

Serious outbreaks have occurred in the past in hospitals treating patients with CCHF. It is important that adequate infection control procedures (barrier nursing) are observed when caring for patients with CCHF.
Contaminated needles, surgical instruments and body waste materials should be safely disposed of using appropriate decontamination procedures. Healthcare workers who have had contact with tissue or blood from patients with CCHF should be followed up with daily temperature and symptom monitoring for 14 days afterwards.

There is no safe and effective vaccine against CCHF available for human use.

Tick awareness

Human infection risk can be minimised by:

Wearing appropriate clothing in tick-infested areas (long sleeved shirt and long trousers tucked into socks). Light coloured fabrics are useful, as it is easier to see ticks against a light background
Check that unfed ticks are not brought home on clothes
Considering use of insect repellents, e.g. DEET ® -containing preparations
Inspecting skin frequently and removing any attached ticks
Checking again for ticks, especially in skin folds, at the end of the day
Making sure that children's head and neck areas, including scalps, are properly checked
Checking that pets do not bring unfed ticks into the home on their fur

Safe tick removal

Remove ticks by gently gripping them as close to the skin as possible, preferably using fine-toothed tweezers or similar implements, and pulling steadily away from the skin. Some veterinary surgeries and pet supply shops sell inexpensive tick removal devices, which may be useful for people frequently exposed to ticks. Lighted cigarette ends or match heads are not recommended.

Further information on CCHF

http://www.who.int/mediacentre/factsheets/fs208/en/

Last reviewed: 20 April 2012