Infection with Crimean-Congo haemorrhagic fever

Naturally infected animals show no clinical signs; experimentally infected animals have shown only transient fever, lethargy and reduced appetite. The disease is seen in humans: sudden high fever, severe headache, back and joint pain, abdominal pain, vomiting, red eyes and jaundice, followed around the fourth day by bruising and uncontrolled bleeding from the nose, gut, uterus, urinary and respiratory tracts.

Crimean-Congo haemorrhagic fever is caused by Crimean-Congo haemorrhagic fever virus, an enveloped, negative-sense RNA virus with a three-segment genome (L, M and S) in the genus Orthonairovirus, family Nairoviridae. Only one serotype is known, although the virus is genetically diverse. In livestock and wild animals infection is subclinical: the virus produces a short, low-level viraemia lasting roughly 2 to 15 days, which is nonetheless enough to infect ticks feeding on the animal. Animals therefore act as silent amplifiers. In people the same virus causes a severe illness that moves through a pre-haemorrhagic phase, a haemorrhagic phase and convalescence, although how it causes disease in humans is not well understood.

The virus occurs in many countries of Asia, Africa, the Middle East and south-eastern Europe, and its range matches that of its main vector, Hyalomma ticks; Rhipicephalus and Dermacentor ticks are secondary vectors. It persists in ticks by passage between life stages, through eggs and between ticks co-feeding on one host. Hyalomma ticks feed on sheep, goats, cattle, hares, deer and hedgehogs. Most birds resist infection, except ostriches, but ground-feeding birds carry infected ticks long distances. People are infected by tick bites, crushing ticks, contact with blood of viraemic animals (for example at slaughter) and from patients in hospitals. Recent detections include Jordan and Spain. It is a WOAH-listed disease and notifiable in many countries.

Because infected animals stay clinically normal, there is no clinical picture in livestock to confuse with other diseases, and infection is found only by testing. Rising antibody prevalence in ruminants, detected by IgG or IgM ELISA or immunofluorescence, marks areas of virus circulation; real-time RT-PCR on serum during viraemia confirms active infection.

Blood (viraemia) in animals; in humans vascular system, skin, liver, gastrointestinal tract, urinary tract, respiratory tract, uterus

No animal vaccine exists. Control ticks on livestock with acaricides or repellents, including before slaughter. Handlers, slaughter workers and vets should avoid tick bites and skin contact with fresh blood, and wear protective clothing.

Animals recover without signs. In humans there is no specific cure and care is supportive; case fatality is 5-80% by strain and setting (WOAH), up to 50% of hospitalised patients (CDC) and near 40% (MSD).