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Viral Hemorrhagic Fever

Introduction.

Viral hemorrhagic fevers (VHF) are among the scariest of viral diseases due to their dramatic symptoms, rapid time course, high mortality rate and lack of effective treatment. VHF have been dramatized in movies such as Outbreak and books such as The Hot Zone that describe the Ebola virus. However, numerous other hemorrhagic viruses exist, including Junin, Machupo, Guanarito, Sabia, Crimean-Congo, Lassa, Dengue, Yellow fever, Chapare, Marburg, Hanta, and Rift Valley. Many of these cause a disease syndrome accompanied by fever and multi-organ system failure which can lead to death.

The Pathogens

VHF viruses fall into 4 major virus families: Arenaviruses, Bunyaviruses, Flaviviruses and Filoviruses.

Virus	Family	Disease	Distribution	Transmission
Ebola	Filovirus	Ebola	Africa	DC
Marburg	Filovirus	Marburg HF	Africa	DC
Dengue fever virus	Flavivirus	Dengue HF	Africa	Vector
Yellow fever	Flavivirus	Yellow fever	Africa	Vector
Sin Nombre virus	Bunyavirus	Hantavirus Pulmonary syndrome	US	DC, inhalation
Hantaan virus	Bunyavirus	HFRS	Asia	DC, inhalation
Nairovirus	Bunyavirus	Crimean Congo HF	Africa	Vector
Phlebovirus	Bunyavirus	Rift Valley fever	Africa	Vector
Lassa virus	Arenavirus	Lassa HF	Africa	DC, inhalation
Junin virus	Arenavirus	Argentine HF	South America	DC, inhalation
Machupo virus	Arenavirus	Bolivian HF	South America	DC, inhalation
Guanarito virus	Arenavirus	Venezuelan HF	South America	DC, inhalation
Sabia virus	Arenavirus	Brazilian HF	South America	DC, inhalation
Chapare virus	Arenavirus	Chapare HF	South America	DC, inhalation

Symptoms/Pathogenesis

Initial symptoms may be mild or severe, but usually include fever and malaise. Headaches, nausea, vomiting, liver damage and myalgia may follow. VHFs feature bleeding (both internal and external) that may be intestinal, respiratory, or from the eyes, often caused by damage to the vascular endothelium.

Diagnosis

Differentiation of VHFs relies largely on patient history, e.g. contact with infected individuals (Ebola), animals (Hanta, Marburg), vectors (Crimean Congo, Dengue), and/or particular geographical locations. Specialized laboratory diagnosis may be necessary and include electron microscopy, antigen-based tests, genetic analysis or even viral culture. Because of the seriousness of VHF, such testing can usually only be done in BSL-4 labs.

Treatment/Prevention

Few treatments exist for VHFs other than supportive care. Rehydration and cardiovascular support can help counter blood loss, but ultimately viral damage to internal organs causes more damage than hemorrhaging alone. Ribavirin (Lassa) and some experimental drugs (Ebola) have been used with limited success. Prevention efforts are also limited to limiting contact with reservoir animals and vectors, as a vaccine exists for only one VHF (Yellow Fever).