Crimean-Congo haemorrhagic fever
Severe and deadly outbreaks

Crimean-Congo hemorrhagic fever is a viral hemorrhagic fever usually transmitted by ticks. It can also be contracted through contact with infected animal tissues. The virus is wide-spread and changes in climate make ticks carrying the virus prevalent in areas where it did not exist before. It also makes epidemics more frequent and serious. The disease is difficult to prevent and treat.

Crimean-Congo hemorrhagic fever has high fatality. The official number of cases per year are low but this is due to the fact that systematic surveillance of this disease is severely lacking.



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What causes Crimean-Congo hemorrhagic fever

Crimean-Congo hemorrhagic fever is caused by a zoonotic virus, member of the genus Orthonairovirus in the family Nairoviridae and order Bunyavirales. This virus is the most genetically diverse of the arboviruses and seven genotypes have been recognized with each having its own geographical area.

The virus has been isolated from cattle, sheep, hares, and mice, and evidence of infection was also found in a range of other species like cats, reptiles, and birds.

Humans usually become infected by tick bites or by contact with blood and tissues from infected animals or other humans who are infected. Ticks in the genus Hyalomma are the principal vectors of the disease.

Infection can also occur from drinking unpasteurized milk, consuming raw meat or liver from freshly slaughtered animals as well as through mucous membranes and broken skin.

Photo: Hyalomma tick

Where is Crimean-Congo hemorrhagic fever found

Crimean-Congo hemorrhagic fever has the most extensive geographic range of the tick-borne viruses affecting humans. It is widespread in Africa, Middle East, Asia, southern and eastern Europe.

In Europe and Asia, the presence of the virus was reported in Spain, Portugal, Hungary, Romania, Bulgaria, Ukraine, Kosovo, Albania, Macedonia, southern Russia, Mongolia, Kazakhstan, and Uzbekistan. However, not all of these countries reported human clinical cases. Antibodies to the virus have been found in 10-15% of the population of Turkey and up to 15% of the Greece population is thought to have antibodies as well.

Soviet scientists first noticed the disease in 1944 they called Crimean hemorrhagic fever in Crimea. Later, in 1956 the virus was found in Congo DRC and found to be antigenically identical. In 1973 the name Crimean–Congo hemorrhagic fever virus was adopted.

Image: Geographical distribution of Hyalomma ticks (WHO)

What are the symptoms of Crimean-Congo hemorrhagic fever

Some infections with the virus are asymptomatic, while others might be mild to severe. Typically, symptoms will appear after a 1 to 3 day incubation period following a tick bite.

Typically the disease starts flu-like with chills, headache, dizziness, sore throat, and joint pain. Gastrointestinal signs like nausea and diarrhea are also often present. Neurological and cardiovascular signs appear in some cases. Sharp mood swings may occur, and the patient may become confused and aggressive. Patients may completely recover following the first stage or they may develop a hemorrhagic syndrome.

The hemorrhagic stage may last from one day to more than a week and typically starts on day 4. The first sign of hemorrhagic syndrome could be a petechia rash on the skin and mucous membranes. This could be followed by the appearance of bruises, which can cover most of the limb. Bleeding in the eye and brain, hepatomegaly (liver enlargement) and splenomegaly (spleen enlargement) are common symptoms as well. In an advanced stage, this will be accompanied by shock, kidney failure, and acute respiratory distress syndrome. The risk of death is 10-40%.

How can Crimean-Congo hemorrhagic fever be prevented

Farmers, shepherds, veterinarians, laboratory workers, and healthcare personnel are at elevated risk of infection.

Prevention involves avoiding tick bites by using special repellents, wearing long pants and long sleeves as well as avoiding areas inhabited by ticks. Skin and clothing should be frequently examined for the presence of ticks and in case ticks are found, they should be removed without touching them with bare hands. De-ticking farm animals before transportation or slaughter is required in endemic areas.

Clothing and wearing gloves are also important when handling the blood and tissue of infected animals, especially in endemic areas. One should avoid drinking unpasteurized milk. It is recommended to thoroughly cook meat and other animal products before consumption and avoid oral contact with raw animal products.

There is currently no vaccine to prevent the disease.

How is Crimean-Congo hemorrhagic fever diagnosed

Crimean-Congo hemorrhagic fever infection can be confirmed using Polymerase chain reaction (PCR) tests, such as the ones made available by the WoIDMo. ELISA tests can also be used and detect antibodies 7 to 9 days after the onset of symptoms.

Early diagnosis and fast treatment reduces the severity of the disease and prevents deaths.

How is Crimean-Congo hemorrhagic fever treated

Treatment for Crimean-Congo hemorrhagic fever is primarily supportive. Care should include careful attention to fluid balance and correction of electrolyte abnormalities, oxygenation, hemodynamic support, and appropriate treatment of secondary infections.

Ribavirin, an antiviral drug, has been used with some success. Treatment is most effective when it is started early in the course of the disease and preferably within 48 hours after the onset of symptoms.

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