Ebola virus disease

Ebola virus disease (EVD) is a severe and frequently lethal disease caused by Ebola virus (EBOV) (1):

• EVD outbreaks typically start from a single case of probable zoonotic transmission, followed by human-to-human transmission via direct contact or contact with infected bodily fluids or contaminated fomites
• EVD has a high case-fatality rate; it is characterized by fever, gastrointestinal signs and multiple organ dysfunction syndrome
• diagnosis requires a combination of case definition and laboratory tests, typically real-time reverse transcription PCR to detect viral RNA or rapid diagnostic tests based on immunoassays to detect EBOV antigens

Virology

• 12 distinct filoviruses have been described (1)
  • the seven filoviruses that have been found in humans belong either to the genus
    • Ebolavirus (Bundibugyo virus (BDBV), Ebola virus (EBOV), Reston virus (RESTV), Sudan virus (SUDV) and Taï Forest virus (TAFV);
    • or to the genus Marburgvirus (Marburg virus (MARV) and Ravn virus (RAVV))
  • the WHO International Classification of Diseases Revision 11 (ICD-11) of 2018 recognizes two major subcategories of filovirus disease (FVD):
    • Ebola disease caused by BDBV, EBOV, SUDV or TAFV, and
    • Marburg disease caused by MARV or RAVV
  • Ebola virus disease (EVD) is defined as a disease only caused by EBOV
  • Ebola disease is caused by viruses from the Ebolavirus genus, filoviruses with a linear single negative-stranded ribonucleic acid (RNA), with 2 species, EBOV and SUDV accounting for most disease burden in humans (2)

Ebola is rare, but outbreaks can occur (3)

• to date, the largest outbreak was in West Africa from 2014 to 2016, which caused approximately 29 000 cases and more than 11 000 deaths
• on May 17, 2026, the World Health Organization (WHO) declared a public health emergency of international concern due to an outbreak of Ebola, which is caused by the Bundibugyo virus, in the Democratic Republic of Congo and Uganda

EBOV is a zoonotic virus, and outside of outbreaks, does not persist in human populations

• the natural reservoir host(s) of Ebola virus (EBOV) has (have) yet to be identified (1)
  • multiple data indicate a direct or indirect role of bats in EBOV ecology, but to date, EBOV has not been isolated from, nor has a near-complete EBOV genome been detected in any wild animal
• clusters and outbreaks are primarily the result of person-to-person transmission of these viruses, which occurs through direct contact with the body, bodily fluids (commonly to health care workers), or contaminated clothes or linens of an infected person (1):
  • EBOV is transmitted by direct, typically non-aerosol, human-to-human contact or contact with infected tissues, bodily fluids or contaminated fomites
  • infectious EBOV has been recovered from breast milk, saliva, urine, semen, cerebrospinal fluid, and aqueous humor, in addition to blood and blood derivatives, and detected in amniotic fluid, tears, skin swabs and stool
• the level of viremia, and thus presumptively the risk of transmission, corresponds with disease severity, with highest concentrations of the virus during later stages of disease

Incubation period and clinical feature (1,2):

• mean incubation period of EVD is 6.22 ± 1.57 days for all routes of exposure
  • 5.85 ± 1.42 days for percutaneous exposure
  • 7.34 ± 1.35 days for person-to-person contact or contact with infected animals
• clinical features
  • early infection (days 1–3 following disease onset)
    • patients present with a non-specific febrile illness (symptoms may include anorexia, arthralgia, headache, malaise, myalgia and rash)
    • progresses in the first week to severe gastrointestinal symptoms and signs (nausea, vomiting and high-volume diarrhoea)
  • onset of detectable viraemia and manifestations of clinical signs and symptoms in most patients occurs 6–10 days after exposure
    • later in the first week of illness following disease onset, patients may have persistent fever and increased gastrointestinal fluid losses and hypotension from dehydration and, to a minor extent, vascular leakage
    • rhabdomyolysis has also been observed
    • note that although EVD is still often referred to as a ‘viral haemorrhagic fever’ because not all patients have overt bleeding manifestations and fever is not always present (1)
  • terminal phase (days 7–12 following disease onset)
    • tissue hypoperfusion and vascular leakage, often in conjunction with dysregulated inflammation, lead to multiple organ dysfunction syndrome and/or damage, including acute kidney injury
    • a subset of patients develop central nervous system manifestations and encephalopathy

Supportive care and treatment of complications are the cornerstones of the treatment of Ebola disease

• at present specific monoclonal antibody therapies are effective only against the EBOV and do not treat other species like Sudan or Bundibugyo (3)

Prognosis (3):

• depends on the severity of symptoms and their access to medical care
• during previous outbreaks of the Bundibugyo virus, 25% to 50% of patients with the infection died

Actions in the event of a possible case

• if Ebola (or another viral haemorrhagic fever) is considered likely, the patient should be isolated (in a side room if possible), with appropriate infection control measures while a detailed risk assessment is carried out. The Advisory Committee on Dangerous Pathogens (ACDP) risk assessment guidance document and algorithm should be used and is available here: https://www.gov.uk/government/publications/viral-haemorrhagic-feveralgorithm- and-guidance-on-management-of-patients

Reference:

1. Jacob ST, Crozier I, Fischer WA 2nd, Hewlett A, Kraft CS, Vega MA, Soka MJ, Wahl V, Griffiths A, Bollinger L, Kuhn JH. Ebola virus disease. Nat Rev Dis Primers. 2020 Feb 20;6(1):13.
2. El Ayoubi LW, Mahmoud O, Zakhour J, Kanj SS. Recent advances in the treatment of Ebola disease: A brief overview. PLoS Pathog. 2024 Mar 15;20(3):e1012038.
3. Zhou S, Malani P. What Is Ebola? JAMA. 2026;336(2):176.