West Africa Ebola Outbreak 2013-2014: Disease, Treatments, and Global Impact

Jill E. Weatherhead, MD; Laila Woc-Colburn, MD

Disclosures

February 03, 2015

In This Article

The Ebola Virus and Ebola Virus Disease

Ebola is a single-stranded RNA filovirus known to cause hemorrhagic fever in humans and nonhuman primates.[1,2,3] The five species of Ebola virus—Zaire, Sudan, Tai Forest, Bundibugyo, and Reston—have different potential virulence.[1] Ebola virus is thought to originate from the fruit bat, which is the natural Ebola virus host, and to be transmitted to humans through contact with infected bodily fluids from such animals as chimpanzees, gorillas, forest antelope, and porcupines, subsequently causing Ebola virus disease (EVD) in humans.[4]

Person-to-person viral transmission occurs through direct contact with infected body fluids, including blood, feces, vomit, semen, urine, and breast milk from a patient who is either symptomatic with or has died of EVD; no data support transmission of EVD through respiratory secretions.[1] Limited data suggest that transmission is possible through contact with contaminated fomites, but no current data support airborne transmission.[1]

After Ebola virus is transmitted between hosts, it penetrates mucosal surfaces and evades the host immune response through blocking type 1 interferon antiviral response, allowing viral replication within monocytes, macrophages, and dendritic cells.[2,3] The virus subsequently transfers through the bloodstream to the liver and spleen, causing dysregulation of the coagulation cascade, release of tissue factor from monocytes and macrophages, reduction of protein C levels, and severe proinflammatory cytokine and chemokine responses.[2,3] The mean incubation period before onset of symptoms is 11.4 days, with 95% of patients displaying symptoms within 21 days after exposure.[5] The viral load increases exponentially at the time of evolving symptoms.[2]

The symptoms of EVD can be nonspecific at initial presentation and may include fatigue, loss of appetite, vomiting, diarrhea, headache, and abdominal pain, an erythematous maculopapular rash, and high oscillating temperatures.[1,2,5] Specific hemorrhagic symptoms (such as unexplained bleeding) have been reported in only 18% of cases in the current epidemic.[5] More commonly, patients develop severe gastrointestinal disease with large-volume fluid loss (up to 10 L/day) and increased endothelial permeability with vascular leakage, causing severe hypovolemic shock.[2,3]

Patients who recover generally begin to do so between days 6 and 11 after symptom onset.[1] However, those with more severe disease may go on to develop mucosal hemorrhage, which has been reported in fewer than 50% of cases, as a late presentation and progress to multiorgan system failure, including acute kidney failure, respiratory failure, and subsequent death.[1,2,6] The infected patient will remain infectious while the virus is still present in bodily fluids, and men can transmit virus through semen for up to 7 weeks after recovery from illness.[4]

The risk for transmission of EVD is dependent on an individual's risk factors. High-risk individuals include those who have had:

Percutaneous or mucous membrane exposure to the blood or body fluids of a person known to be infected with Ebola virus;

Direct skin contact with a person known to be infected, without use of personal protective equipment (PPE);

Processing blood or body fluids of a person known to be infected, without use of PPE; or

Direct contact with the dead body of a person who had EVD without use of PPE.[1]

Low-risk individuals are those who have household contact with Ebola virus and those in close contact in healthcare or community setting.[1]

The Centers for Disease Control and Prevention (CDC) defines "possible EVD" as elevated body temperature; subjective fever; or symptoms including fatigue, vomiting, diarrhea, abdominal pain, or unexplained hemorrhage, plus epidemiologic risk factors, such as contact with a symptomatic Ebola-infected patient within 21 days of onset of symptoms.[2,7]

The diagnosis of EVD is typically made through detection of the virus antigen by enzyme-linked immunosorbent assay (ELISA) or viral RNA sequences using reverse-transcriptase polymerase chain reaction (RT-PCR) in the blood or other body fluids.[1] Ebola virus can be detected by RT-PCR within 3-10 days of symptom onset.[1,2] PCR can also be used to verify clearance of viremia when patients are recovering.[1]

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