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.
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 :
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.
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