Description

• An enveloped, negative-stranded RNA virus with a characteristic filamentous structure (family Filoviridae)
• A high mortality rate, combined with the absence of specific antiviral treatment and no proven vaccine, makes Ebola virus one of the most virulent human pathogens.
• Incubation period between 2 and 21 days; most cases present the 2nd week after exposure.
• Patients become infected through contact with body fluids from an infected human or animal.
• The predominant clinical syndrome involves substantial volume loss due to vomiting and diarrhea, leading to circulatory collapse. Frank hemorrhage is less common. Thus, the prior description of Ebola as a “hemorrhagic fever” has given way to the term Ebola virus disease (EVD).

Epidemiology

• Four principal strains of the virus are known to cause disease in humans: Zaire, Sudan, Bundibugyo, and Taï Forest.
• The Zaire strain caused the historically largest and most widespread outbreak of Ebola (West Africa, 2014 to 2015).
• 2014 to 2016 West Africa Ebola outbreak: A total of 28,616 Ebola cases were reported in Guinea, Liberia, and Sierra Leone, with 11,310 deaths. These included 881 infected health care workers.
• On August 1, 2018, the Ministry of Public Health of the Democratic Republic of Congo declared a new outbreak of Ebola. As of September 4, 2018, a total of 127 cases have been reported with 87 deaths (1).
• Reservoir: Indirect evidence strongly indicates the fruit bat as a host organism.
• Outbreaks start as a zoonotic, animal–human species jump and spread through human–human contact.
• Ebola virus enters the body through mucous membranes, breaks in the skin, or parenterally.
• Ebola virus can also be spread through direct contact with the skin of an infected patient.
• The most infectious body fluids are blood, feces, and vomit. Ebola virus persists longer in semen, CSF, and aqueous humor. All body fluids should be considered infectious and handled with maximum (biosafety level 4) precautions.

Etiology and Pathophysiology

• The virus spreads through direct contact (through broken skin or mucous membranes) with
  • Blood or body fluids of an infected person (alive or recently deceased)
  • Objects (e.g., clothing, bedding, needles, and syringes) that have been contaminated with body fluids from an infected person (alive or dead)
  • Infected fruit bats or primates (apes and monkeys)
• Male–female sexual transmission has been documented (virus persists in semen).
• The early steps of infection lead to aberrant immune responses in monocytes, macrophages, dendritic cells, and hepatocytes. This leads to a cytokine cascade, loss of endothelial cell adhesion, and vascular leakage/collapse.

Pregnancy Considerations

• Atypical presentation of EVD may be observed in pregnancy—abdominal pain, preterm labor, vaginal bleeding, premature rupture of membranes, or spontaneous miscarriages.
• Fetal death may occur even with maternal recovery.
• Ebola virus RNA has been detected at low levels in breast milk up to 16 months after onset of symptoms. There have been no documented maternal–child transmissions attributed to nursing.

Risk Factors

Health care providers, family, and friends in close contact with Ebola-infected patients are at highest risk.

General Prevention

• A vaccine derived from a chimpanzee adenovirus and a human recombinant vesicular stomatitis virus (rVSV) vaccine have been studied (2).
• The rVSV-ZEBOV demonstrated protection against EVD in a trial conducted by the WHO and other international partners in Guinea in 2015 (3).