Ebola virus — clinical features, spread, treatment and prevention

Aetiology. Ebolavirus is an enveloped, single-stranded, negative-sense RNA filovirus (family Filoviridae). Six species are recognised, four of which cause human disease: Zaire ebolavirus — much the most virulent, with case fatality of 25–90% — Sudan, Bundibugyo and Taï Forest ebolavirus. The natural reservoir is believed to be fruit bats, with index cases arising from contact with infected bats or non-human primates (bushmeat). Incubation 2–21 days.

Spread. Human-to-human transmission is by direct contact with blood or body fluids — vomit, stool, urine, saliva, sweat, semen, breast milk — of a symptomatic or dead person, entering through broken skin or mucous membranes, or through contact with contaminated surfaces, linen and needles. It is not airborne. The classic outbreak amplifiers are traditional burial practices involving washing of the body, and nosocomial transmission to healthcare workers where PPE is inadequate. Critically, the virus persists in immune-privileged sites — semen for 18 months or more, ocular fluid, CNS and breast milk — causing sexual transmission, late relapse, and new outbreaks seeded from survivors.

Clinical features. Abrupt onset of fever, profound weakness, myalgia, headache and sore throat (the "dry" phase), followed at days 3–10 by the "wet" phase — high-volume vomiting and profuse watery diarrhoea causing massive fluid and electrolyte loss, hypovolaemic shock, acute kidney injury and hepatitis. Haemorrhage occurs in only about 20% (petechiae, mucosal and gastrointestinal bleeding) — death at days 6–16 is usually from hypovolaemic and septic shock with severe electrolyte derangement, not from bleeding, which is the point examiners look for. Late features: encephalopathy, seizures, DIC and multi-organ failure. Survivors develop post-Ebola syndrome — arthralgia, uveitis which may cause blindness, hearing loss and cognitive difficulty.

Diagnosis. RT-PCR on whole blood is the confirmatory test; it may be negative in the first 3 days, so a symptomatic patient must be retested at 72 hours. Antigen-detection rapid tests are used for triage, and ELISA detects IgM and IgG. Supportive findings: early leucopenia then neutrophilia, thrombocytopenia, markedly raised transaminases with AST greater than ALT, rising creatinine, and profound hypokalaemia and hyponatraemia. All specimens are category A infectious substances requiring high-level biosafety handling and specialised transport. In an endemic region the differential includes malaria — test every patient — typhoid, Lassa fever, meningococcaemia and dengue.

Treatment. The foundation, which by itself substantially reduces mortality, is aggressive supportive care: high-volume oral and intravenous fluid and electrolyte replacement with particular attention to potassium, magnesium and calcium, antiemetics, nutritional support, analgesia, correction of hypoglycaemia, and empirical antimalarials and antibiotics for co-infection, with organ support as needed. Specific therapy for Zaire ebolavirus: two monoclonal antibody products are approved on the basis of the PALM trial — Inmazeb (atoltivimab/maftivimab/odesivimab) and Ebanga (ansuvimab) — both of which substantially reduced mortality compared with ZMapp and remdesivir. No approved therapy exists for Sudan virus disease.

Prevention. Isolation with strict barrier nursing and full PPE, dedicated staff and equipment, safe injection practice and safe waste disposal; contact tracing with 21-day monitoring; safe and dignified burials; community engagement; and avoidance of bushmeat. Vaccines against Zaire ebolavirus: rVSV-ZEBOV-GP (Ervebo), a single-dose live vaccine, WHO-prequalified and used in ring vaccination of contacts, contacts-of-contacts and healthcare workers; and the two-dose Ad26.ZEBOV / MVA-BN-Filo (Zabdeno / Mvabea) regimen for preventive use. Survivors must use condoms and undergo semen testing until two negative PCR results.

Outbreak response has become dramatically faster and now follows a standard template. In the 2025 Democratic Republic of Congo (Kasai) outbreak of Zaire ebolavirus, declared in September 2025 and declared over in December 2025, ring vaccination with Ervebo and treatment with the licensed monoclonals were deployed within days of declaration — the fastest response yet achieved, and one now formalised in WHO's outbreak playbook alongside pre-positioned vaccine stockpiles. For Sudan virus disease, against which neither the licensed vaccine nor the licensed monoclonal antibodies are effective, candidate vaccines are held in a "trial-ready" stockpile so that randomised ring-vaccination trials can be launched within days, as was done in Uganda's 2022 and 2025 outbreaks.