Crimean-Congo Hemorrhagic Fever

Crimean-Congo hemorrhagic fever (CCHF) also known as Congo Fever, Central Asian Hemorrhagic Fever, Hungribta (blood taking), Khunymuny (nose bleeding), Karakhalak (black death) is a zoonotic viral disease that is asymptomatic in infected animals, but a serious threat to humans. Human infections begin with nonspecific febrile symptoms, but progress to a serious hemorrhagic syndrome with a high case fatality rate. It is caused by Crimean-Congo hemorrhagic fever virus (CCHFV). This virus is a member of the genus Nairovirus in the family Bunyaviridae. Although the causative virus is often transmitted by at least 31 species of ticks, animal-to-human and human-to-human transmission also occur. Members of the genus Hyalomma seem to be the principal vectors. Transovarial, transstadial and venereal transmission occur in this genus. Hemorrhages are an important source of exposure for other people, particularly family members and healthcare workers. This disease is a particular threat to farmers and other agricultural workers, veterinarians, laboratory workers and hospital personnel. This disease occurs in much of Africa, the Middle East and Asia, as well as parts of Europe. Changes in climatic conditions could expand the range of its tick vectors, and increase the incidence of disease. The CCHF virus is also a potential bioterrorist agent; it has been listed in the U.S. as a CDC/NIAID Category C priority pathogen. CCHFV can be inactivated by disinfectants including 1% hypochlorite and 2% glutaraldehyde. It is also destroyed by heating at 56°C (133°F) for 30 min.

Infections in Humans

The infections become apparent on average after 5 to 6 days. The first sign is a sudden onset of fever with chills, severe headache, dizziness, photophobia, neck pain, myalgia and arthralgia. Nausea, vomiting, non-bloody diarrhea and abdominal pain, bradycardia are also common. The hemorrhagic phase develops after several days. It is usually short, lasting on average 2 to 3 days. A petechial rash may be the first symptom which is followed by petechiae, ecchymoses and large bruises on the skin and mucous membranes. Hematemesis, melena, epistaxis, hematuria, hemoptysis and bleeding from venipuncture sites are also common. Splenomegaly and hepatomegaly can also be seen. Some patients die from hemorrhages, hemorrhagic pneumonia or cardiovascular disturbances. In patients who survive, recovery begins 10 to20 days after the onset of illness. The average case fatality rate is 30-50%, but mortality rates from 10% to 80% have been reported in various outbreaks. The mortality rate is usually higher for nosocomial infections than after tick bites; this may be related to the virus dose.

Infections in Animals:

CCHFV can be found in many wild and domesticated mammals and has been isolated from a number of species including cattle, sheep, goats, hares, hedgehogs, dogs and mice (Mastomys spp.). Mammals become viremic and can transmit CCHFV in their blood and tissues. Antibodies have been reported in horses, donkeys, pigs, rhinoceroses, giraffes, buffalo and other mammalian species. Most species of birds are seronegative and are thought to be resistant to infection; however, antibodies can be found in ostriches. CCHFV infections are asymptomatic in animals other than experimentally inoculated newborn rodents (laboratory mice, rats and Syrian hamsters). The only symptom in experimentally infected sheep and cattle is a transient, mild elevation in body temperature. Deaths occur only in newborn rodents. Serology can identify animals that have been infected or exposed to CCHFV.

Diagnostic Tests :

Crimean-Congo hemorrhagic fever can be diagnosed by isolating CCHFV in a variety of cell lines including SW-13, Vero, LLC-MK2 and BHK-21 cells from blood, plasma or tissues (lung, liver, spleen, bone marrow, kidney and brain). Animal inoculation into newborn mice is more sensitive than culture, and can detect the virus for a longer period. Virus isolation must be carried out in maximum biocontainment laboratories (BSL-4). CCHFV can also be identified by indirect immunofluorescence or reverse transcription-polymerase chain reaction (RT-PCR), real-time RT-PCR assays, ELISA. It can also be diagnosed by serology using indirect immunofluorescence or ELISA tests.

Prevention :

Treatment is mainly supportive. Ribavirin is used in some human cases. In endemic regions, prevention depends on avoiding bites from infected ticks and contact with infected blood or tissues. Measures to avoid tick bites include tick repellents, environmental modification (brush removal, insecticides), avoidance of tick habitat and regular examination of clothing and skin for ticks. Acaricides can be used on livestock and other domesticated animals to control ticks. Strict universal precautions are necessary when caring for human patients.