CRIMEAN-CONGO HF-CCHF

During the summers of 1944 and 1945 over 200 cases of a severe, acute, febrile illness accompanied by marked haemorrhagic manifestations occurred in the USSR in the Steppe region of the Western Crimea. Many of the cases were among troops of the then Soviet Union who were helping with the harvest. Virus was isolated from blood samples of patients with acute disease and from the tick Hyalomma marginatum marginatum. It was later realised that a similar disease had been known for many years in other areas of the USSR, particularly Central Asian republics, and the same syndrome has since been described in areas bordering the Black and Caspian Seas and Bulgaria and former Yugoslavia.

In 1969, it was shown that the virus causing CCHF was identical to the virus named Congo which had been isolated in 1956 from the blood of a febrile child in Zaire. This virus is widely spread in East and West Africa.

More recently, CCHF or antibody to it, has been shown to have appeared in Dubai, Iraq, South Africa, Pakistan, Greece, Turkey, Albania, Afghanistan, and India. Geographical variation in virulence has been observed, for example, the disease in Africa, where haemorrhagic phenomena and deaths are only rarely reported, does not seem to be as virulent as in Asia.

Probably because CCIHF is associated with severe haemorrhagic features, secondary cases are relatively common. In an outbreak in Saudi Arabia, one case resuscitated in an accident and emergency unit gave rise to seven secondary cases. In 1967, five laboratory-acquired cases were recognised. Hospital-associated outbreaks were described in Pakistan in 1976 and in Dubai in 1980. In November 1996, 15 cases of CCHF were confirmed in South Africa. All of the patients worked in the slaughtering unit of the same ostrich farm. Ostriches, like other birds, are thought to be fairly resistant to infection with CCHF, but they undoubtedly suffer heavy burdens of Hyalomma spp., which could be vectors of the disease.

Crimean-Congo haemorrhagic fever virus and its diagnosis

The CCHF virus is a member of the bunyvirus family of RNA viruses, and is classified as a Nairovirus. It is related to the Hazara virus, found in ticks in Pakistan, and to Nairobi sheep disease virus. It has been isolated from goats, sheep, cattle, hares, hedgehogs and a number of species of ticks associated with these mammals. The infected mammals develop high viraemias, which last for approximately one week, but clinical illness is rare.

Humans may become infected by tick bites, by contamination with body contents from disrupted ticks, or by contact with the blood, tissues or body fluids of infected animals. Clinical disease in infected humans is common and often severe. There is a high viraemia early in the illness.

Early diagnosis is possible using antigen detection by immunolluorescence techniques. Some laboratories use reverse transcriptase PCR methods. IgM antibodies are often detectable after the first five to seven days of fever, but their concentration diminishes significantly after about 10 days, and is replaced by rising IgG levels. The virus is readily cultured in commonly-available cell lines such as monkey kidney (VERO) cells.

Clinical features

The incubation period is about two to seven days, and has not been recorded as longer than 12 days. Illness begins abruptly with high fever, myalgia, headache, vomiting and pain in the epigastrium, lower back and thighs. Loose stools, dry cough and relative bradycardia may be present.

Some patients recover quite suddenly after seven or eight days, but up to 75% begin to show haemorrhagic features after three to five days. A petechial rash often appears in the throat quickly followed by haematemesis, nosebleeds, melaena conjunctival injection and haemorrhages and haernaturia. Despite high viraemia, there is often a marked neutrophilia.

The liver is enlarged and tender, liver and tissue transaminases are elevated and disseminated intravascular coagulation (DIC) may follow. Some patients gradually recover after 10 to 20 days, but in many death occurs on the seventh to ninth day, following a period of shock, oliguria and, sometimes, respiratory distress syndrome.

Treatment

There is evidence that CCHF responds to treatment with ribavirin (Tribavirin), with amelioration of fever and lessening or avoidance of haemorrhagic features. The use of tribavirin is complicated in these patients by its tendency to cause significant anaemia, mainly due to haemolysis. In the UK supplies of intravenous tribavirin are maintained at High-Security Infectious Diseases Units (HSIDUs). Laboratory facilities are also available for carrying out patient management pathology tests in secure laboratory facilities, staffed by specially-trained pathologists.

Intensive supportive management is required at an early stage and sometimes for prolonged periods by cases of CCHF. Convalescence is often slow, with debility lasting for some weeks after recovery.

Public Health Measures

The use of insecticides such as pyrethroids to de-tick farm animals is important. In many endemic areas this is a requirement before animals are transported or delivered for slaughter. Simple tick avoidance by humans includes the use of insect repellents and adequate clothing and footwear, as well as inspection for adherent ticks during washing and when changing clothes.

Excellent infection control measures are important in protecting against hospital-acquired cases. This should be borne in mind when feverish patients with evidence of bleeding require resuscitation or intensive care. Good staff training and supervision is as important as the provision of adequate disposable equipment and protection clothing. Healthcare staff or family members suffering significant blood contamination or percutaneous exposure could be offered tribavirin as prophylaxis, but there are no data about its efficacy. In some East European countries, hyperimmune serum is available, but its efficacy is not well quantified, and international standards of potency and safety are not in force.

Congo Crimean haemorrhagic fever is a notifiable or reportable disease in many non-endemic countries, including the UK.