Viral Hemorrhagic Fever(s)
Viral hemorrhagic fever (VHF) facts*
*Viral hemorrhagic fever facts by Charles Patrick Davis, MD, PhD
Viral hemorrhagic fevers are group of illnesses caused by viruses that cause vascular damage that result in symptomatic bleeding (hemorrhage).
Hemorrhagic fever viruses are mainly zoonotic diseases caused by viruses that usually reside in an animal or arthropod hosts that may serve as vectors.
Viral hemorrhagic fevers are usually seen associated with only one particular of species and consequently are usually contained in geographically restricted areas; however, if the virus is introduced accidentally to humans it becomes widespread (for example, the current Ebola outbreak).
Hemorrhagic fever viruses are usually transmitted among animal or arthropod hosts; however, the viruses carried in these animal or arthropods can be transmitted to humans when humans come in contact with the urine, feces, saliva, or other bodily fluids of infected animals or arthropods, including if the animal is killed and eaten. In some instances, once the viruses infect humans, person-to-person transmission can occur when an uninfected person comes in contact with bodily fluids or (with some viruses) a bite by an arthropod vector.
Symptoms of viral hemorrhagic fever include fatigue, fever, weakness, dizziness, and muscle aches; patients with more severe infections show bleeding under the skin, internal organs, or even from bodily orifices like the mouth, eyes, or ears. Some patients develop severe diarrhea that may also be bloody, and severely ill patients present with shock, delirium, seizures, kidney failure, and coma that often ends in death.
Patients with viral hemorrhagic fevers usually receive only supportive therapy; there is no other established cure for viral hemorrhagic fevers. However, ribavirin (Rebetol, Copegus) has been effective in treating some individuals with Lassa fever, and treatment with convalescent-phase plasma has been used with success in a few patients -- other experimental antiviral agents have also been tried in a few patients.
Prevention and control of hemorrhagic fevers is difficult; except for yellow fever and Argentine hemorrhagic fever, no vaccines have been made commercially available so that prevention efforts are concentrated on avoiding contacts with the host species, vectors, or humans infected with the viruses.
Scientists and researchers are addressing the threat of viral hemorrhagic fevers to humans by attempting to develop immunological, molecular, and containment methods to prevent these hemorrhagic fevers.
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.
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