Viral Haemorrhagic Fevers
What are Viral Haemorrhagic Fevers?
The term "Viral Haemorrhagic Fever" (VHF) is often used to describe a severe syndrome often accompanied by haemorrhage (bleeding). They are caused by several distinct families of viruses. For ease of understanding their prevention, they are classified by means of transmission as in the Table below. Important examples are Crimean-Congo Haemorrhagic Fever(CCHF), Ebola and Marburg Haemorrhgic Fevers, Lassa Fever, Rift Valley Fever(RVF), Dengue Haemorrhagic fever (DHF), Yellow Fever and Smallpox. Dengue Fever and Yellow Fever are usually described separately while smallpox had already been eradicated.
Table Viral haemorrhagic fevers of man classified by route of transmission
Signs and symptoms vary by the type of VHF, but in the early stages they exhibit similar nonspecific symptoms of fever, headache, muscle aches and malaise. Patients with severe cases of VHF often show signs of bleeding under the skin, in body orifices like mouth, eyes or ears or in internal organs. Over 50% of all cases die eventually.
How do they spread?
These viruses naturally reside in animal reservoir hosts, like rodents. Rodents transmit the viruses through human contact with their urine, fecal matter, saliva or other body excretions, as in HFRS. Lassa fever virus is carried by rodents and transmitted by excreta, either aerosol or by direct contact. The hosts of some viruses like Ebola and Marburg viruses are however still unknown.
Insect vectors like mosquitoes or ticks transmit VHF through bites of human or when a human crushes a tick. CCHF is transmitted by ticks. RVF and Dengue Fever are transmitted by mosquito bites.
Humans may also get infected when they care for or slaughter infected animals. For instance, RVF can be acquired by direct contact with blood or tissues of infected animals like sheep, including consumption of unpasteurized milk. For Ebola or Marburg viruses, they can spread from an infected person to another person, directly through close contact with infected people or their body fluids; or indirectly through contact with objects contaminated with infected body fluids, e.g. contaminated syringes and needles.
How to prevent them?
Although the risk for travelers to acquire the diseases is very low, travelers visiting rural or forest areas may be exposed to infection. With the exception of Argentinian Haemorrhagic Fever and Yellow Fever, no vaccine exist's that can protect against these diseases. Therefore, prevention efforts concentrate on avoiding contact with host species. As many of the hosts that carry haemorrhagic fever viruses are rodents, disease prevention efforts focus on their control.
Mosquitoes and tick control are important to prevent spread of haemorrhagic fever viruses transmitted through insect vectors.
For those haemorrhagic fever viruses that can be transmitted from one person to another, close physical contact with infected people and their body fluids should be avoided.
How to treat them?
There is no specific treatment for the disease. Patients must be managed in isolation facilities to prevent the spread of the infection. As close contact with a severely ill patient is a high risk factor for transmission, health care workers should put on protective gears and adopt strict infection control practice when caring for suspected patient.