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Zaire ebolavirus Disease (Ebola Virus Disease)

Overview

Zaire ebolavirus (commonly called Ebola virus) is a highly pathogenic filovirus that causes Ebola virus disease (EVD), a severe and often fatal hemorrhagic fever. The virus was first identified during simultaneous outbreaks in Nzara (South Sudan) and Yambuku (Democratic Republic of the Congo, DRC) in 1976, with the latter occurring near the Ebola River—hence the name.

• Who it affects: All ages and sexes can be infected, but frontline health‑care workers, family caregivers, and people who handle wildlife (especially bats, non‑human primates, and antelopes) are at highest risk.
• Geographic prevalence: Outbreaks have been confined almost exclusively to sub‑Saharan Africa. Between 1976 and 2022, the World Health Organization (WHO) recorded > 35,000 confirmed or probable cases, with a case‑fatality rate (CFR) ranging from 25 % to 90 % depending on the outbreak and access to care.
• Recent activity: The 2014‑2016 West Africa epidemic (mainly caused by the Makona strain) resulted in 28,616 cases and 11,310 deaths. The DRC experienced the largest Zaire‑strain outbreak (2018‑2020) with 3,470 confirmed cases and 2,276 deaths (CFR ≈ 65 %).

Because of its high transmissibility, rapid progression, and lack of widely available curative therapy, Ebola is classified as a Category A bioterrorism agent by the U.S. Centers for Disease Control and Prevention (CDC) [1].

Symptoms

Symptoms typically appear 2‑21 days after exposure (average ≈ 8‑10 days). The disease progresses through three phases: prodromal, early organ involvement, and late-stage (often hemorrhagic). Not all patients develop every symptom.

Prodromal (Days 1‑4)

• Fever (≥ 38 °C / 100.4 °F)
• Severe headache
• Muscle or joint pain (myalgia, arthralgia)
• Fatigue, weakness
• Sore throat
• Loss of appetite

Early Organ Involvement (Days 5‑7)

• Vomiting (often non‑bloody)
• Diarrhea (may become watery, sometimes with blood)
• Abdominal pain
• Rash (maculopapular, may appear on chest, arms, and legs)
• Conjunctival injection (red eyes)

Late‑Stage / Hemorrhagic Phase (Days 8‑12+)

• Bleeding from gums, nose, or gastrointestinal tract
• Bruising or petechiae (tiny red spots) on skin
• Internal bleeding (e.g., in the liver or kidneys)
• Multiorgan failure (kidney, liver, and adrenal insufficiency)
• Hypotension and shock
• Altered mental status (confusion, agitation, seizures)

Because symptoms overlap with malaria, typhoid, Lassa fever, and other viral hemorrhagic fevers, laboratory confirmation is essential.

Causes and Risk Factors

Cause – The Virus

Zaire ebolavirus is an enveloped, single‑stranded, negative‑sense RNA virus. It infects humans through direct contact with:

• Blood, saliva, sweat, vomit, feces, urine, or other bodily fluids of an infected person
• Contaminated objects (needles, syringes, clothing, bedding)
• Infected animal tissue or fluids (bats are the suspected natural reservoir; non‑human primates are intermediate hosts)

Key Risk Factors

• Close contact with a sick person: caring for patients, performing medical procedures without adequate personal protective equipment (PPE).
• Occupational exposure: health‑care workers, laboratory staff, mortuary workers.
• Traditional burial practices: washing or touching the deceased.
• Travel to or from outbreak zones: especially without pre‑travel counseling.
• Living in forested areas: higher chance of contact with bats or infected wildlife.
• Immunocompromise: may increase susceptibility, though the primary driver is exposure.

Diagnosis

Rapid, accurate diagnosis is critical for patient care and infection control. The gold‑standard tests detect viral RNA or antigens.

Laboratory Tests

• Real‑time reverse transcription polymerase chain reaction (RT‑PCR): Detects viral RNA within 1‑3 days of symptom onset. Sensitivity > 95 %.
• Antigen‑capture enzyme‑linked immunosorbent assay (ELISA): Useful for early detection when viral load is high.
• Serology (IgM/IgG antibodies): Helpful for retrospective diagnosis; antibodies appear ~10 days after infection.
• Virus isolation (cell culture): Performed only in high‑containment (BSL‑4) labs; rarely used clinically.

Supportive Laboratory Findings

• Leukopenia (low white‑blood‑cell count)
• Thrombocytopenia (low platelet count)
• Elevated liver enzymes (AST, ALT)
• Prolonged prothrombin time (PT) and activated partial thromboplastin time (aPTT)
• Metabolic acidosis, electrolyte disturbances

Clinical Diagnosis

In an outbreak setting, a patient with compatible symptoms and an epidemiologic link (e.g., exposure to a known case) may be classified as a "probable case" pending laboratory confirmation.

Treatment Options

There is no single “cure,” but early aggressive supportive care dramatically improves survival. In recent years, several antivirals and monoclonal antibodies have demonstrated efficacy.

Supportive Care (mainstay)

• Fluid resuscitation: Intravenous (IV) crystalloids or colloids to correct dehydration and maintain blood pressure.
• Electrolyte management: Replace potassium, magnesium, calcium as needed.
• Oxygen therapy: For hypoxemia; mechanical ventilation if respiratory failure develops.
• Renal replacement therapy: Hemodialysis for acute kidney injury.
• Blood product transfusion: Platelets, fresh frozen plasma, or packed red cells for coagulopathy and anemia.
• Fever control: Acetaminophen (paracetamol) – avoid NSAIDs unless specifically indicated.

Antiviral & Monoclonal Antibody Therapies

• Inmazeb (atoltivimab‑mafabivimab‑odesivimab): A triple‑monoclonal antibody cocktail approved by the U.S. FDA (2020) for Zaire ebolavirus infection. In a Phase III trial, mortality fell from 53 % (control) to 28 % when given within 5 days of symptom onset.
• Ebanga (ansuvimab‑zykl): Single‑dose monoclonal antibody approved (2020) with similar efficacy; preferred for ease of administration.
• Remdesivir: Broad‑spectrum antiviral; limited data suggest modest benefit, not first‑line.
• Favipiravir: Investigational; results mixed.

Experimental Options (used under compassionate use protocols)

• ZMapp (triple‑antibody cocktail) – early outbreak product, now largely superseded.
• Polymerase‑targeted siRNA therapeutics – still in clinical trials.

Lifestyle / Adjunctive Measures

• Strict isolation and use of PPE for caregivers.
• Psychological support for patients and families.
• Nutrition: High‑calorie, high‑protein oral rehydration solutions when oral intake is possible.

Living with Zaire ebolavirus Disease

Survivors often face a long recovery phase, sometimes called “post‑Ebola syndrome.” Below are practical tips for patients and families.

• Follow‑up appointments: Regular labs to monitor liver/kidney function, coagulation, and immune status for at least 12 months.
• Vision and hearing checks: Uveitis and hearing loss are reported in up to 20 % of survivors.
• Neuro‑cognitive rehab: Address memory loss, concentration difficulties, and mood disorders with physical therapy, occupational therapy, and counseling.
• Vaccination: The rVSV‑ZEBOV (Ervebo) vaccine is recommended for close contacts and health‑care workers; it can also boost immunity in survivors.
• Stigma reduction: Educate community members; disclose status only to trusted health officials.
• Infection‑control at home: Continue safe handling of bodily fluids for at least 21 days after recovery; use dedicated linens and disinfect surfaces with 0.5 % chlorine solution.

Prevention

Because no oral prophylactic drug exists, prevention focuses on avoiding exposure and interrupting transmission.

Vaccination

• rVSV‑ZEBOV (Ervebo): Single‑dose, live‑attenuated vaccine with ~97 % efficacy against Zaire ebolavirus (WHO, 2022). Recommended for ring vaccination—contacts of confirmed cases and frontline workers.

Personal Protective Measures

• Wear appropriate PPE (gloves, impermeable gown, face shield, N95 or higher respirator) when caring for patients.
• Practice strict hand hygiene with soap and water or alcohol‑based hand rubs.
• Avoid contact with wildlife (bats, primates) and raw bushmeat; cook meat thoroughly.
• Use safe burial practices: body bags, disinfectant, trained burial teams.
• Travel advisories: Follow WHO and CDC guidance before visiting endemic areas.

Environmental Controls

• Disinfect surfaces with 0.5 % chlorine solution (1:100 bleach) or EPA‑approved virucidal agents.
• Proper waste management: incineration or deep burial of contaminated materials.

Complications

Even with optimal care, Ebola can cause serious short‑ and long‑term sequelae.

• Multiorgan failure: Rapid deterioration of liver, kidney, and adrenal function.
• Severe hemorrhage: Gastrointestinal, mucosal, or intracranial bleeding.
• Neurologic complications: Encephalitis, seizures, peripheral neuropathy.
• Ocular disease: Uveitis leading to vision loss (≈ 15 % of survivors).
• Joint and muscle pain: Chronic arthralgia can persist for months.
• Psychiatric sequelae: Depression, anxiety, post‑traumatic stress disorder (PTSD).
• Recrudescence: Rare re‑emergence of virus in immune‑privileged sites (e.g., eye, testes) months after recovery.

When to Seek Emergency Care

References

1. World Health Organization. Ebola virus disease. WHO Fact Sheet. Updated 2023.
2. Centers for Disease Control and Prevention. Ebola (Ebola Virus Disease). CDC. Accessed May 2026.
3. Mayo Clinic. Ebola virus disease. Mayo Clinic. 2024.
4. NIH National Institute of Allergy and Infectious Diseases. Clinical Trials of Inmazeb and Ebanga. NIAID. 2022.
5. Cleveland Clinic. Ebola Virus Disease: Symptoms, Diagnosis, Treatment. Cleveland Clinic. 2025.
6. WHO Ebola Vaccination Recommendations. WHO. 2022.

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