Types of RNA virus causing hemorrhagic fevers

The viral haemorrhagic fevers (VHFs) are caused by four types of ribonucleic acid (RNA) virus:

• Filoviruses cause Ebola and Marburg.
• Arenaviruses cause Lassa fever, Argentine haemorrhagic fever (HF), Bolivian HF, Brazilian HF and Venezuelan HF.
• Bunyaviruses cause Korean HF (Hantavirus), Rift Valley fever (RVF) and Crimean-Congo HF (CCHF).
• Flaviviruses cause yellow fever and dengue fever.

Ebola virus, Marburg virus, Lassa fever, Hantavirus, yellow fever and dengue fever have their own articles in which they are covered in rather more detail. They are all highly infectious and lead to a potentially fatal disease with fever, malaise, vomiting, mucosal and gastrointestinal bleeding, oedema, and hypotension.

Filoviridae

This group includes the Marburg and Ebola viruses. Most outbreaks are in, or originate from, Africa. In the Congo and in Kenya, bats have been implicated as a possible source of an outbreak of Marburg infection.^[1][2] The mortality is often around 80% and healthcare workers are often amongst the victims. Marburg and Ebola are covered in more detail in their respective artic

Arenaviridae

The most significant of these viruses is Lassa fever. Lassa fever is transmitted directly to humans by rodents, insect bites, especially mosquitoes, from primates and from patients. Incubation period is 5-16 days. Nosocomial infection is very common where precautions against cross-infection are minimal. Medical staff are also at risk of catching it from patients. Up to 300,000 infections and 5,000 deaths from Lassa fever are estimated to occur yearly, the highest incidence occurring in Sierra Leone, Liberia and Guinea.^[3] Lassa fever has been imported into Germany, the Netherlands, the UK and the USA by travellers from Africa on commercial airlines.^[4] Other Arenaviridae have incubation periods of 7-15 days.

Bunyaviridae

They include Rift Valley fever (RVF), Crimean-Congo haemorrhagic fever (CCHF), and a number of Hantaviruses. RVF and CCHF are both spread by arthropods. They have incubation periods of 2-5 days and 3-12 days respectively. RVF is an important African pathogen that is transmitted to humans and livestock by mosquitoes and by the slaughter of infected livestock.^[5] CCHF virus is carried by ticks and causes a fulminant disease that can be transmitted by aerosol particles. Outbreaks of CCHF have occurred in Africa, Asia and Europe.
Hantaviruses exist throughout the world, causing two main syndromes. They are haemorrhagic fever with renal syndrome (HFRS) and Hantavirus pulmonary syndrome (HPS). They are divided into Old World Hantaviruses like the Korean virus, which usually cause HFR, and New World Hantaviruses that cause HPS. Both are transmitted by rodents. A new Hantavirus that was called Sin Nombre virus, caused an outbreak of highly lethal HPS in the southwestern USA in 1993. Sin nombre is Spanish for 'without name'. Incubation periods for Hantavirus infection are in the range of 9-35 days.
A recent steep increase in reported Hantavirus infections was noted in a known endemic area in southern Germany. This was thought to be due to an increase in the population of the natural animal reservoir - the bank vole.^[6]

Flaviviridae

Yellow fever and dengue fever are the best known diseases caused by this group. Mosquitoes are the vectors for both. Yellow fever is found in tropical Africa and South America and dengue fever is found in Asia, Africa and the Americas. It has recently been shown that dengue virus targets mannose receptors on macrophages.^[7]