Viral haemorrhagic fevers are a group of illnesses that are caused by several distinct families of viruses: arenaviruses, filoviruses, bunyaviruses and flaviviruses. Some of these cause relatively mild illnesses, whilst others can cause severe, life-threatening disease. Examples of these viruses and the diseases they cause are shown below.
Because the viruses depend on their animal hosts for survival, they are usually restricted to the geographical area inhabited by those animals. The viruses are endemic in areas of Africa, South America and Asia. Human cases or outbreaks of viral haemorrhagic fever occur sporadically and irregularly, and cannot easily be predicted. Recent outbreaks of Ebola infection have occurred in Central Africa. Occasionally, humans may acquire infection from animal hosts that have been exported from their native habitats, as occurred when laboratory workers in Germany handled imported monkeys infected with Marburg virus. Environmental conditions in England and Wales do not support the natural reservoirs of infection. See VHF Maps
Humans are not the natural host for these viruses which normally live in wild animals. Rodents are the main reservoirs of haemorrhagic fever viruses - examples include the multimammate rat, cotton rat and house mouse. Humans may acquire infection when they come into close contact with animal hosts, their carcasses during slaughtering, or their droppings. Some of the viruses, such as yellow and Crimean-Congo fever are transmitted between animal species, including humans, by the bites of tick or mosquito vectors. For some of the viruses, for example Ebola, the animal host is not known, but contact with monkeys has been implicated in some cases of infection. Lassa, Ebola, Marburg and Crimean-Congo viruses can be transmitted from person-to-person through close contact with symptomatic patients or contaminated body fluids.
This varies according to the type of virus, but is rarely longer than 21 days. If symptoms occur more than 21 days after contact with a potential source of infection, then they are unlikely to be due to viral haemorrhagic fever.
Symptoms also vary according to the type of virus, but initial symptoms generally include fever, fatigue, dizziness, muscle aches and weakness. In early stages, symptoms may resemble other infections - see here for differential diagnoses. Patients with severe disease may show signs of bleeding under the skin, from body orifices like the mouth, eyes and ears, or into internal organs. Severely ill patients may also show signs of shock, kidney failure and nervous system malfunction including coma, delirium and seizures.
Some viral haemorrhagic fevers can be treated with anti-viral drugs, however other infections can only be managed supportively.
A vaccine is available to protect against yellow fever, and is recommended for travellers to endemic areas.
No vaccines are available against other types of haemorrhagic fever viruses. Therefore, prevention measures concentrate on avoiding contact with host species.
Environmental conditions in England and Wales do not support the natural reservoirs of infection, thus cases do not occur here, except as an imported disease. Such imported cases in travellers returning from endemic areas are rare: there have been 8 cases of Lassa fever since 1980, and a single confirmed case of Crimean Congo haemorrhagic fever in 2012.
More information can be found in factsheets on the World Health Organization website: