Viral Hemorrhagic Fever(s)
What are viral hemorrhagic fevers?
Viral hemorrhagic fevers (VHFs) refer to a group of illnesses that are caused
by several distinct families of viruses. In general,
the term "viral hemorrhagic fever" is used to describe a severe multisystem
syndrome (multisystem in that multiple organ systems in the body are affected).
Characteristically, the overall vascular system is damaged, and the body's ability to regulate itself is
impaired. These symptoms are often accompanied by hemorrhage (bleeding);
however, the bleeding is itself rarely life-threatening. While some types of
hemorrhagic fever viruses can cause relatively mild illnesses, many of these
viruses cause severe, life-threatening disease.
The Special Pathogens Branch (SPB) primarily works with hemorrhagic fever
viruses that are classified as biosafety level four (BSL-4) pathogens. A
list of these viruses appears in the
SPB disease information index. The Division
of Vector-Borne Infectious Diseases, also in the National Center for Infectious
Diseases, works with the non-BSL-4 viruses that cause two other hemorrhagic
fevers, dengue hemorrhagic fever and
yellow fever.
How are hemorrhagic fever viruses grouped?
VHFs are caused by viruses of four distinct families: arenaviruses,
filoviruses, bunyaviruses, and flaviviruses. Each of these families share a
number of features:
- They are all RNA viruses, and all are covered, or enveloped, in a fatty
(lipid) coating.
- Their
survival is dependent on an animal or insect host, called the natural reservoir.
- The viruses are geographically restricted to the areas where their host species
live. Humans are not the natural reservoir for any of these viruses.
- Humans are
infected when they come into contact with infected hosts. However, with some
viruses, after the accidental transmission from the host, humans can transmit
the virus to one another.
- Human cases or outbreaks of hemorrhagic fevers caused
by these viruses occur sporadically and irregularly. The occurrence of outbreaks
cannot be easily predicted.
- With a few noteworthy exceptions, there is no cure
or established drug treatment for VHFs.
In rare cases, other viral and bacterial
infections can cause a hemorrhagic fever; scrub typhus is a good example.
Next: What carries viruses that cause viral hemorrhagic fevers? »
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