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CBRNE - Viral Hemorrhagic Fevers

Author: David C Pigott, MD, Associate Professor, Department of Emergency Medicine, University of Alabama at Birmingham
Contributor Information and Disclosures

Updated: May 29, 2009

Introduction

Background

Viral hemorrhagic fevers (VHFs) are a group of febrile illnesses caused by RNA viruses from several viral families. These highly infectious viruses lead to a potentially lethal disease syndrome characterized by fever, malaise, vomiting, mucosal and gastrointestinal (GI) bleeding, edema, and hypotension. The 4 viral families known to cause VHF disease in humans include the Arenaviridae, Bunyaviridae, Filoviridae, and Flaviviridae. General characteristics of these viral families can be found in the table below.Table 1. Viral Families Causing Viral Hemorrhagic Fever

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Arenaviridae

Arenaviridae are spread to humans by rodent contact and include Lassa virus in Africa and several rare South American hemorrhagic fevers such as Machupo, Junin, Guanarito, and Sabia. Lassa virus is the most clinically significant of the Arenaviridae, accounting for serious morbidity and mortality in West Africa.

Lassa fever first appeared in Lassa, Nigeria, in 1969. It has been found in all countries of West Africa and is a significant public health problem in endemic areas. In populations studied, Lassa fever accounts for 5-14% of hospitalized febrile illnesses. Its natural reservoir is a small rodent whose virus-containing excreta is the source of transmission.

This group includes Rift Valley fever (RVF) virus, Crimean-Congo hemorrhagic fever (CCHF) virus, and several hantaviruses. The RVF and CCHF viruses are both arthropod-borne viruses. RVF virus, an important African pathogen, is transmitted to humans and livestock by mosquitos and by the slaughter of infected livestock. CCHF virus is carried by ticks and causes a fulminant, highly pathogenic form of VHF notable for aerosol transmission of infective particles. Outbreaks of CCHF have occurred in Africa, Asia, and Europe.

Filoviridae

The most notorious of the VHF viruses, including Ebola and Marburg viruses, belong to the Filoviridae family. Ebola virus first was described in 1976 after outbreaks of a febrile, rapidly fatal hemorrhagic illness were reported along the Ebola River in Zaire (now the Democratic Republic of the Congo) and Sudan. Sporadic outbreaks have continued since that time, usually in isolated areas of central Africa. An outbreak in Kikwit, Zaire, in 1995 led to 317 confirmed cases, with an 81% mortality rate. Two thirds of the patients were among health care workers caring for infected individuals. An outbreak in Uganda in late 2000 resulted in 425 cases and claimed 225 lives.

In September 2007, the cause of a VHF outbreak in the Congo was identified as Ebola. Ebola has 4 distinct subtypes: Ebola-Zaire, Ebola-Sudan, Ebola-Ivory Coast, and Ebola-Reston, a form that causes illness in nonhuman primates, and as has been recently discovered, in pigs.¹ A 2007 Ebola outbreak in Uganda, however, has been attributed to a new form of Ebola. This new Ebola subtype, which appears to be closely related to Ebola-Ivory Coast, has been given the proposed name Bundibugyo Ebola virus (named after the Bundibugyo district in Western Uganda).²

The natural reservoir of Ebola virus remains unknown, although some recent studies have suggested that bats may be a potential reservoir for Ebola.³

Yellow fever and dengue fever are the most well known diseases caused by flaviviruses. Both are mosquito-borne; yellow fever is found in tropical Africa and South America, and dengue fever is found in Asia, Africa, and the Americas. They are notable for their significant effect on prior military campaigns and their continued presence throughout endemic areas.

Pathophysiology

The primary defect in patients with viral hemorrhagic fever (VHF) is that of increased vascular permeability. Hemorrhagic fever viruses have an affinity for the vascular system, leading initially to signs such as flushing, conjunctival injection, and petechial hemorrhages, usually associated with fever and myalgias. Later, frank mucous membrane hemorrhage may occur, with accompanying hypotension, shock, and circulatory collapse. The relative severity of the clinical presentation may vary depending on the virus in question, amount, and route of exposure.

In acute disease, patients are extremely viremic, and messenger ribonucleic acid (mRNA) evidence of multiple cytokine activation exists. In vitro studies reveal these cytokines lead to shock and increased vascular permeability, the basic pathophysiologic processes most often seen in viral hemorrhagic fever infection. Another prominent pathologic feature is pronounced macrophage involvement. Inadequate or delayed immune response to these novel viral antigens may lead to rapid development of overwhelming viremia. Extensive infection and necrosis of affected organs also are described. Hemorrhagic complications are multifactorial and are related to hepatic damage, consumptive coagulopathy, and primary marrow injury to megakaryocytes. Aerosol transmission of some viral hemorrhagic fever infections is reported among nonhuman primates and likely is a mode of transmission in patients with severe infection.

Multisystem organ failure affecting the hematopoietic, neurologic, and pulmonary systems often accompanies the vascular involvement. Hepatic involvement varies with the infecting organism and is at times seen with Ebola, Marburg, RVF, CCHF, and yellow fever. Renal failure with oliguria is a prominent feature of HFRS seen in Hantavirus infection and may be seen in other VHFs as intravascular volume depletion becomes more pronounced. Bleeding complications are particularly prominent with Ebola, Marburg, CCHF, and the South American arenaviruses.

Frequency

United States

Cases of viral hemorrhagic fever in the United States are extremely rare and usually are found in patients who recently have visited endemic areas or among those with potential occupational exposure to hemorrhagic fever viruses. Lassa fever has been reported in the United States in travelers from West Africa and was most recently reported in the United States in August 2004. In 1994, a virologist working with Sabia, a Brazilian HF virus, accidentally contracted the disease. Sporadic cases of HPS due to Sin Nombre virus continue to be reported throughout the southwestern United States.⁴

No human cases of Ebola or Marburg virus disease have been reported in the United States. In 1989, an outbreak of hemorrhagic fever among imported macaque monkeys in Reston, Virginia, led to the discovery of Ebola-Reston, a variant of Ebola virus that originated in the Philippines and does not cause disease in humans.

International

Lassa fever is responsible for an estimated 100,000-300,000 infections per year, with 5,000 deaths. Cases have been reported throughout West Africa, particularly in Nigeria, Sierra Leone, Guinea, and Liberia. Other arenaviruses are responsible for sporadic VHF outbreaks throughout South America.

Rift Valley fever (RVF) virus and Crimean-Congo hemorrhagic fever (CCHF) are responsible for intermittent epidemics in Africa (for RVF) and in areas of Africa, Asia, and Europe (for CCHF). HFRS due to Hantavirus infection continues to be an ongoing health concern, particularly in Asia, affecting up to 200,000 patients annually.

Ebola virus appears sporadically in endemic areas of the former Zaire and Sudan. Ebola virus also has been reported in Gabon, the Ivory Coast, and Uganda. Outbreaks appear to propagate in hospital settings, often involving health care providers.

Yellow fever continues to be a serious problem in tropical areas of South America and Africa, where vaccination is not widespread. The World Health Organization estimates that approximately 200,000 cases per year occur in Africa. Dengue HF is endemic in Southeast Asia, and more than 1 million cases occur annually.

Mortality/Morbidity

Case-fatality rates of patients with VHF vary from less than 10% (eg, in dengue HF) to approximately 90%, as has been reported in patients with Ebola-Zaire and the recent Angola Marburg outbreak. The most recent outbreak of Ebola-Sudan in Uganda had a 50% case-fatality rate.

Complications from VHF infection include retinitis, orchitis, hepatitis, transverse myelitis, and uveitis. In patients who recover from Lassa fever infection, deafness is the most common complication. Spontaneous abortion also is common. Renal insufficiency is associated with HFRS infection.

Race

No racial predilection has been identified, although cases have originated in African areas.

Sex

No predilection for either sex has been identified.

Age

VHF affects all ages according to exposure and local demographics.

Clinical

History

• Obtain a detailed travel history, paying particular attention to recent travel to tropical or rural areas, such as Central or South America (yellow fever, arenaviruses), West Africa (Lassa fever), or to endemic portions of Central Africa (Ebola, Marburg, RVF, CCHF). Ask about contact with potential arthropod or rodent reservoirs.
  • Since the natural reservoir for Ebola and Marburg viruses is unknown, contact with infected monkeys or humans is not a prerequisite for transmission of infection.
  • Direct contact with rodents infected with hemorrhagic fever viruses (eg, arenaviruses, hantaviruses) is not necessary for transmission of infection, since aerosolized excreta may transmit infection.
• Contacts of patients with known viral hemorrhagic fever (VHF), especially family members or health care workers caring for infected patients, are at risk for infection if appropriate barrier precautions are not used.
  • Transmission of VHF has occurred from the reuse of unsterile needles and syringes used for treatment of infected patients.
  • Transmission of VHF also has occurred to individuals handling the deceased in preparation for burial or to individuals involved in the slaughter of infected livestock (as in RVF or CCHF).
• Because of their extreme pathogenicity and potential for transmission by fine particle aerosol, VHF viruses are considered potential biological warfare agents. In addition, Dr Ken Alibek, the former Deputy Director of the once massive Soviet bioweapons program, Biopreparat, claims Soviet scientists successfully had produced a stable Marburg virus biological weapon that could be delivered as an aerosol.
  • Large numbers of military personnel with VHF symptoms suggest such an attack.
  • An outbreak of VHF in a nonendemic area also suggests a biological warfare attack.
• Incubation periods for VHF vary from 2-21 days.
• The initial symptoms correspond to development of viremia and include the following:
  • High fever
  • Headache
  • Fatigue
  • Abdominal pain
  • Myalgias
  • Prostration
• In more advanced disease, signs and symptoms include the following:
  • Hematemesis and bloody diarrhea
  • Generalized mucous membrane hemorrhage
  • Rash
  • Altered mental status and cardiovascular collapse (preterminal events)

Physical

Depending on the progress of the disease, patients with viral hemorrhagic fever (VHF) initially may present with minimal signs, suggesting a more benign viral syndrome. Maintain a high index of suspicion. As the disease progresses, more classic findings are present as follows:

• Fever
• Pharyngitis
• Conjunctival injection
• Nondependent edema
• Petechial or ecchymotic rash
• GI bleeding
• Hypotension and/or shock
• Most hemorrhagic fevers, except Rift Valley fever, can produce a variety of cutaneous findings that are principally caused by vascular instability and bleeding abnormalities. Such findings include flushing, petechiae, purpura, ecchymoses, and edema.
• The Old World arenavirus causing Lassa fever results in the greatest amount of edema of any of the hemorrhagic fever viruses. Additionally, no bleeding abnormalities are present.
• The New World arenaviruses (Junin, Machupo, Sabia, and Guanarito) cause less edema and variable amounts of petechiae, purpura, ecchymoses, palatal hyperemia, and mucosal hemorrhage.
• The most severe hemorrhage from a hemorrhagic fever virus follows infection with the Congo Crimean hemorrhagic fever virus.
• Hantaviruses can cause a relatively distinctive eruption with a petechial eruption around the neck and on the anterior and posterior axillary folds, arms, and trunk. A sunburn-like flush is seen on the head, neck, and upper chest and back and may be accompanied by facial edema. Sometimes, a morbilliform eruption occurs. Oral and conjunctival surfaces may develop severe hemorrhages.

• The greatly feared filoviruses (Marburg and Ebola) exhibit characteristic exanthems that are best seen in fair-skinned patients. Soft palatal hyperemia accompanies the flu-like prodrome and is followed between days 5 and 7 by a nonpruritic, centripetal, pinhead-sized papular, erythematous exanthem. Within 24 hours, this can develop into large and coalescent, well-demarcated, sometimes hemorrhagic macules and papules. In severe cases, hemorrhage exudes from mucous membranes, venipuncture sites, and body orifices.
• Dengue virus causes a characteristic erythematous exanthem with striking islands of sparing.

Causes

• See Table 1.

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