What are viral hemorrhagic fevers?

Viral hemorrhagic 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 in the table.

Table: hemorrhagic fever viruses and the diseases they cause

Where are viral hemorrhagic fevers found?

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 hemorrhagic fever occur sporadically and irregularly, and cannot easily be predicted. Recent outbreaks of Ebola infection have occurred in Western 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.

What is the bioterrorism potential of these viruses?

Theoretically, they could be released deliberately as an aerosol, although airborne infection of humans through small-particle aerosols has not been clearly demonstrated and is likely to be difficult to achieve. The viruses are not highly infectious from person to person, requiring close contact with contaminated bodily fluids for transmission. In addition, the viruses cannot survive for long outside the body.

How do you catch viral hemorrhagic fever?

Humans are not the natural host for these viruses; they normally live in wild animals. Rodents are the main reservoirs of hemorrhagic 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.

How long can you have the infection before developing symptoms?

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 hemorrhagic fever.

What are the symptoms of viral hemorrhagic fever?

Symptoms also vary according to the type of virus, but initial symptoms generally include fever, fatigue, dizziness, muscle aches and weakness. 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.

Can viral hemorrhagic fever be prevented or treated?

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 hemorrhagic fever viruses. Therefore, prevention measures concentrate on avoiding contact with host species.

• Because many of the hosts that carry hemorrhagic fever viruses are rodents, disease prevention efforts include controlling rodent populations and keeping rodents away from homes and workplaces.
  
• For hemorrhagic fever viruses spread by vectors, prevention measures also include controlling the population of ticks and mosquitoes, and preventing bites by using screens, wearing proper clothing and using repellent spray.
  
• For hemorrhagic fever viruses that can be transmitted from person to person, great care needs to be taken when nursing patients, including isolation and the wearing of gloves, gowns and masks, in order to prevent the spread of infection. There have been several documented instances when health care staff contracted Ebola and Marburg viruses from infected patients.
  
• Some viral hemorrhagic fevers can be treated with anti-viral drugs, while other infections can only be managed supportively.

How common is viral hemorrhagic fever?

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: between 1997 and 2000, there were only 7 notified cases of suspected viral hemorrhagic fever, only 2 of which were confirmed.

Where can I find more information about viral hemorrhagic fevers?

More information about specific viruses and diseases can be found on the website of the World Health Organisation: