Haemorrhagic fevers are viral infections; important examples are Ebola and Marburg haemorrhagic fevers, Crimean–Congo haemorrhagic fever (CCHF), Rift Valley fever (RVF), Lassa fever, Hantavirus diseases, dengue and yellow fever.
Hantavirus diseases, dengue and yellow fever are described separately.
Viruses belonging to several families. Ebola and Marburg belong to the Filoviridae family; hantaviruses, CCHF and RVF belong to the Bunyaviridae family; Lassa fever virus belongs to the Arenaviridae family; and dengue and yellow fever belong to the Flaviviridae family.
Viruses that cause haemorrhagic fevers are transmitted by mosquitoes (dengue, yellow fever, RVF), ticks (CCHF), rodents (Hantavirus, Lassa) or bats (Ebola, Marburg). For Ebola and Marburg viruses, humans have been infected from contact with tissues of diseased non-human primates (monkeys and apes) and other mammals, but most human infections have resulted from direct contact with the body fluids or secretions of infected patients. Humans who develop CCHF usually become infected from a tick bite but can also acquire the virus from direct contact with blood or other infected issues from livestock or from infected patients. RVF can be acquired either by mosquito bite or by direct contact with blood or tissues of infected animals (mainly sheep), including consumption of unpasteurized milk. Lassa fever virus is carried by rodents and transmitted by excreta, either as aerosols or by direct contact. Some viral haemorrhagic fevers have been amplified in hospitals by nosocomial transmission resulting from unsafe procedures, use of contaminated medical devices (including needles and syringes) and unprotected exposure to contaminated body fluids.
Nature of the disease
The haemorrhagic fevers are severe acute viral infections, usually with sudden onset of fever, malaise, headache and myalgia followed by pharyngitis, vomiting, diarrhoea, skin rash and haemorrhagic manifestations. The outcome is fatal in a high proportion of cases (more than 50%).
Diseases in this group occur widely in tropical and subtropical regions. Ebola and Marburg haemorrhagic fevers and Lassa fever occur in parts of sub-Saharan Africa. CCHF occurs in the steppe regions of central Asia and in central Europe, as well as in tropical and southern Africa. RVF occurs in Africa and has recently spread to Saudi Arabia and Yemen. (Maps can be found on WHO website.)
Risk for travellers
Very low for most travellers. However, travellers visiting rural or forest areas in countries or areas at risk may be exposed to infection.
None (except for yellow fever).
Avoid exposure to mosquitoes and ticks and contact with rodents, non-human primates or bats. Avoid unpasteurized milk.