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viral hemorrhagic fevers

Monday 6 February 2006

Viral hemorrhagic fevers (VHFs) are systemic infections characterized by fever and hemorrhage. They are caused by enveloped RNA viruses in four different families: arenaviruses, filoviruses, bunyaviruses, and flaviviruses.

Although structurally distinct, these viruses all depend on an animal or insect host for survival and transmission.

VHF viruses are restricted geographically to areas in which their hosts reside. Humans are infected when they come into contact with infected hosts or insect vectors, but humans are not the natural reservoir for any of these viruses. Although uncommon, human-to-human transmission can occur.

The infectious dose for VHF viruses appears to be low. Hemorrhagic fever viruses produce a spectrum of illnesses, ranging from relatively mild acute disease characterized by fever, headache, myalgia, rash, neutropenia, and thrombocytopenia to severe, life-threatening disease in which there is sudden hemodynamic deterioration and shock. Human cases or outbreaks of hemorrhagic fevers are sporadic and unpredictable.

There are no cures or effective drug therapy for viral hemorrhagic fevers. VHF viruses are potential biologic weapons owing to their infectious properties, morbidity and mortality, and the absence of therapy and vaccines.

The pathogenesis of hemorrhagic fever viruses is not well understood. These viruses enter the bloodstream by a number of routes, including the bite of an insect, and following inhalation or mucous membrane exposure. All (except for hantaviruses) cause disease during the period of viremia. Endothelial cell infection occurs with the majority of VHF viruses.

The hemorrhagic manifestations are due to thrombocytopenia or severe platelet or endothelial dysfunction.

Typically, there is increased vascular permeability. There may be necrosis and hemorrhage in many organs, and often there is widespread hepatocellular necrosis.

Infection with many VHF viruses stimulates cytokine production, which may contribute to severe cytopathic effects or disseminated intravascular coagulation (DIC).

Types

- arthropod-borne viral infections prevalent in southern Africa

  • chikungunya fever
  • Sindbis fever
  • West Nile fever (West Nile virus)
  • yellow fever
  • Rift Valley fever

- viral infections associated with rodents

  • Lassa fever

- viral infection associated with monkeys

  • rickettsial infections
  • tick-bite fever
    • spotted fever of tick typhus occurring in southern Africa)
    • Q fever
  • bacterial infections
    • coccal infections
    • plague septicemia
    • meningococcal
    • staphylococcal
    • streptococcal septicemia
  • blood protozoal infections
    • malaria
    • trypanosomiases

- viral infections

  • rubella

- non-infectious diseases

  • Gasser syndrome
  • Henoch-Schonlein purpura
  • viperine snakebite

See also

- hemorrhagic state (systemic hemorrhages)
- infectious agents (infecting organisms)
- viruses
- rickettsiae
- bacterias
- protozoas
- coagulation cascade
- fibrin formation
- fibrin deposits in microvasculature (thrombotic microangiopathy)
- aggregation of platelets and entanglement of platelets
- marked thrombocytopenia
- bleeding
- coagulation factors

  • prothrombin

References

- Gear JH. Hemorrhagic fevers, with special reference to recent outbreaks in southern Africa. Rev Infect Dis. 1979 Jul-Aug;1(4):571-91. PMID: 399369