Crimean-Congo haemorrhagic fever (CCHF) is a viral disease caused by tick-borne virus (Nairovirus). It is a zoonotic (could be transmitted from animals to humans) vector-borne disease. CCHF causes severe illness in humans and has a case-fatality rate of up to 40%.
The disease was first described in the Crimea (former USSR) in 1944 and given the name Crimean haemorrhagic fever. In 1969, it was recognized that the pathogen causing Crimean haemorrhagic fever was the same as that responsible for an illness identified in 1956 in the Congo and linkage of the both place names resulted in the current name for the disease and the virus.
The disease is widespread in many countries in Africa, Europe, Middle East and Central Asia with sporadic outbreaks recorded in Kosovo, Albania, Iran, and Turkey.
CCHF outbreaks constitute a threat to public health services because of its epidemic potential (biological capacity of a pathogen to cause disease in a particular environment), its high case fatality ratio (10-40%), its potential for nosocomial (hospital acquired infection) outbreaks and the difficulties in its treatment and prevention.
Onset of symptoms is sudden, with fever, myalgia, (muscle ache), dizziness, neck pain and stiffness, backache, headache, sore eyes and photophobia (sensitivity to light).
There may be nausea, vomiting, diarrhoea, abdominal pain and sore throat early on, followed by sharp mood swings and confusion. After two to four days, the agitation may be replaced by sleepiness, depression and lassitude, and the abdominal pain may localize to the upper right quadrant, with detectable hepatomegaly (liver enlargement).
Other clinical signs include tachycardia (fast heart rate), lymphadenopathy (enlarged lymph nodes), and a petechial rash (a rash caused by bleeding into the skin) on internal mucosal surfaces, such as in the mouth and throat, and on the skin. The petechiae may give way to larger rashes called ecchymoses, and other haemorrhagic phenomena such as melaena (bleeding from the upper bowel, passed as altered blood in the faeces), haematuria (blood in the urine), epistaxis (nosebleeds) and bleeding from the gums.
There is usually evidence of hepatitis, and severely ill patients may experience rapid kidney deterioration, sudden liver failure or pulmonary failure after the fifth day of illness.
The mortality rate from CCHF is approximately 30%, with death occurring in the second week of illness. In patients who recover, improvement generally begins on the ninth or tenth day after the onset of illness.
CCHF is caused by virus belongs to family Bunyaviridae, genus Nairovirus. Since it is enveloped virus, it can be readily inactivated. CCHF virus is stable for up to 10 days in blood kept at 400 C.
Vector (living organisms that can transmit infectious diseases between humans or from animals to humans) – The common vector of CCHF is the member of Hyalomma genus, the family Ixodidae. These are hard ticks and suck blood from animals and humans. Both male and female ticks can act as a vector for disease transmission.
CCHF virus may infect a wide range of wild animals and domestic ruminant animals such as hares, rats, camel, cattle, sheep and goats.
Environmental factors: Ecological changes, poverty, social instability, poor health services, and absence of standard infection control practices have contributed to increased transmission of the CCHF virus.
Mode of transmission-
Animal to human transmission-CCHF virus may be transmitted to human either by bite of hard tick or through contact with infected animal blood or tissues during and immediately after slaughter. The majority of cases have occurred in people involved in the livestock industry, such as agricultural workers, slaughterhouse workers and veterinarians.
Human to human transmission– Humans can become infected if blood, body fluids and wastes from patients with the disease comes into contact with broken skin or mucous membranes, as occurs when medical care personnel sustain accidental needle stick injury. Hospital-acquired infections can also occur due to improper sterilization of medical equipment, reuse of needles and contamination of medical supplies.
Incubation periods-Incubation period depends on the mode of transmission of disease. It is usually one to three days when infected with tick bite with maximum nine days.
The incubation period following contact with infected blood or tissues is usually five to six days, with a documented maximum of 13 days.
CCHF virus is highly infectious in the hospital settings. Nosocomial (hospital acquired) infections are common after exposure to blood and secretions of infected persons.
There are no rapid diagnostic tests.
Diagnosis of suspected CCHF is performed in specially-equipped, high bio-safety level laboratories.
IgG and IgM antibodies detection in serum by enzyme-linked immunoassay (the “ELISA” or “EIA” methods) from about day six of illness. IgM remains detectable for up to four months, and IgG levels decline but remain detectable for up to five years.
Virus detection in blood or tissue samples-Patients with fatal disease do not usually develop a measurable antibody response and in these individuals, as well as in patients in the first few days of illness, diagnosis is achieved by virus detection in blood or tissue samples. The virus may be isolated from blood or tissue specimens in the first five days of illness, and grown in cell culture. Viral antigens may sometimes be shown in tissue samples using immunofluorescence or EIA.
The polymerase chain reaction (PCR) and Real-Time PCR, a molecular method for detecting the viral genome, has been successfully applied in diagnosis.
CCHF is a severe disease in humans, with a high mortality rate. Treatment for CCHF is primarily supportive.
General supportive therapy is the mainstay of patient management in CCHF. Intensive monitoring to guide volume and blood component replacement is required.
The antiviral drug has been used in treatment of established CCHF infection with apparent benefit. Both oral and intravenous formulations seem to be effective.
Appropriate treatment of secondary infections should be instituted.
There is no safe and effective vaccine currently available for human use. CCHF being a zoonotic vector-borne disease multi-sectoral integrated approach involving medical, veterinary and entomology specialties is the key to prevention and control of outbreaks. Infection in people can be reduced by raising awareness of the risk factors and educating people about the measures they can take to reduce exposure to the virus.
Public health advice should focus on following aspects:
i) Reducing the risk of tick-to-human transmission:
- wear protective clothing (long sleeves, long trousers);
- wear light coloured clothing to allow easy detection of ticks on the clothes;
- use approved acaricides (chemicals intended to kill ticks) on clothing;
- use approved repellent on the skin and clothing;
- regularly examine clothing and skin for ticks; if found, remove them safely;
- seek to eliminate or control tick infestations on animals or in stables and barns; and
- avoid areas where ticks are abundant and seasons when they are most active.
ii) Reducing the risk of animal-to-human transmission:
- Wear gloves and other protective clothing while handling animals or their tissues in endemic areas, notably during slaughtering, butchering and culling procedures in slaughterhouses or at home;
- Separate or restrict movements of animals(quarantine) before they enter slaughterhouses or routinely treat animals with pesticides two weeks prior to slaughter.
iii) Reducing the risk of human-to-human transmission in the community:
- avoid close physical contact with CCHF-infected people;
- wear gloves and protective equipment when taking care of ill people;
- wash hands regularly after caring for or visiting ill people
Controlling infection in health-care settings:
Health-care workers caring for patients with suspected or confirmed CCHF, or handling specimens from them, should implement standard infection control precautions. These include basic hand hygiene, use of personal protective equipment, safe injection practices and safe burial practices.
Samples taken from people with suspected CCHF should be handled by trained staff working in suitably equipped laboratories.
Recommendations for infection control while providing care to patients with suspected or confirmed Crimean-Congo haemorrhagic fever should follow those developed by WHO for Ebola and Marburg haemorrhagic fever.