Chapter 216: The Filovirids: Orthoebolavirus and Orthomarburgvirus Infections

Chapter 216 | Part 5: Infectious Diseases

KEY CLINICAL POINTS

• Filovirids (Ebola and Marburg viruses) are RNA viruses causing severe hemorrhagic fevers with high case-fatality rates (44.6% globally).
• Transmission occurs via direct contact with bodily fluids, with no aerosol or respiratory droplet spread. Prevention relies on PPE, vaccination, and outbreak control.
• Diagnosis requires RT-PCR, antigen detection, or electron microscopy, with testing conducted in biosafety level 4 labs.
• Treatment includes monoclonal antibodies (mAb114, REG-EB3) and supportive care for complications like renal failure and coagulopathy.
• Long-term sequelae in survivors include chronic fatigue, neurological deficits, and potential viral persistence in immune-privileged tissues.

1. DEFINITION & OVERVIEW

Filovirids are RNA viruses in the family Filoviridae, causing severe hemorrhagic fevers. They are classified into two genera: Orthoebolavirus (Ebola, Reston, Sudan, Taï Forest) and Orthomarburgvirus (Marburg, Ravn). These viruses are WHO Risk Group 4 pathogens, requiring maximum containment.

1.1 Taxonomy

Filoviridae includes nine genera, with Orthoebolavirus and Orthomarburgvirus causing human disease. The family is characterized by linear, nonsegmented, negative-sense RNA genomes ≈ 19 kb in length.

1.2 Clinical Presentation

Initial symptoms resemble influenza, progressing to severe multiorgan dysfunction, hemorrhage, and shock. The disease course is marked by viremia, immune suppression, and coagulopathy.

2. EPIDEMIOLOGY

As of 2024, 35,608 cases and 15,886 deaths were reported globally. Outbreaks are endemic in equatorial Africa and Central/South America, with transmission linked to nonhuman primates, bats, and human-to-human contact. Case-fatality rates vary by virus (e.g., 50% for Ebola vs. 25% for Reston).

2.1 Risk Factors

Occupational exposure (healthcare workers), contact with infected animals (bats, nonhuman primates), and poor infection control in healthcare settings increase risk.

2.2 Demographics

Outbreaks disproportionately affect children, healthcare workers, and individuals in resource-limited settings. Mortality is higher in older adults and those with comorbidities.

3. ETIOLOGY & PATHOPHYSIOLOGY

Filoviruses replicate in macrophages and dendritic cells, suppressing innate immunity via VP35/VP40 proteins. They induce cytokine storms, endothelial dysfunction, and disseminated intravascular coagulation. Viral persistence in immune-privileged tissues (e.g., semen, CNS) may lead to recrudescence.

3.1 Viral Structure

Filovirions are pleomorphic filaments (91–98 nm wide) with GP spikes. The genome encodes seven structural proteins (NP, VP35, VP40, GP, VP30, VP24, L) and nonstructural proteins in Orthoebolavirus.

3,2 Pathogenesis

Viral entry via GP-mediated fusion causes cell lysis. Immune evasion through interferon suppression and viral dissemination to organs leads to multiorgan failure and coagulopathy.

4. CLINICAL FEATURES

Initial phase: fever, headache, myalgia, rash. Second phase: gastrointestinal symptoms, hemorrhage, shock, and neurological deficits. Severe cases present with acute renal failure, hepatic dysfunction, and disseminated intravascular coagulation.

4.1 Symptomatology

Nonspecific prodrome (fever, fatigue), followed by gastrointestinal, respiratory, and neurological symptoms. Hemorrhagic manifestations include petechiae, ecchymoses, and gastrointestinal bleeding.

4.2 Laboratory Findings

Leukopenia, thrombocytopenia, elevated liver enzymes, hyperbilirubinemia, and coagulopathy (prolonged PT/PTT, elevated D-dimers).

5. DIFFERENTIAL DIAGNOSIS

Distinguish from malaria, typhoid fever, sepsis, Lassa fever, yellow fever, and other viral hemorrhagic fevers. Key differentiators include epidemiologic context, clinical presentation, and laboratory findings (e.g., absence of malaria parasites in blood smears).

6. INVESTIGATIONS & DIAGNOSIS

Diagnosis requires RT-PCR (detecting viral RNA), antigen-capture ELISA, or electron microscopy. Testing must be conducted in BSL-4 labs. Serology is less reliable due to cross-reactivity.

6.1 Diagnostic Criteria

Clinical suspicion + epidemiologic risk factors + positive RT-PCR or antigen detection. Postmortem diagnosis uses PCR on tissue samples.

6.2 Laboratory Safety

Samples must be inactivated with guanidinium isothiocyanate or irradiation before handling. Biosafety level 4 protocols are mandatory.

7. MANAGEMENT & TREATMENT

Supportive care is critical. Approved therapies include monoclonal antibodies (mAb114, REG-EB3) for Ebola. Antiviral drugs (favipiravir) and immunomodulators are under investigation. Management of complications (e.g., renal failure, coagulopathy) is prioritized.

7.1 Therapeutics

mAb114 (ansuvimab-zykl) and REG-EB3 (atoltivimab, maftivimab, odesivimab-ebgn) reduce mortality in EVD. Treatment must be initiated early post-diagnosis.

7.2 Supportive Care

Fluid resuscitation, oxygen therapy, renal replacement, and management of electrolyte imbalances. Anticoagulation is used cautiously to prevent thrombosis.

8. PROGNOSIS & COMPLICATIONS

Case-fatality rates vary by virus (44.6% overall). Survivors may experience prolonged fatigue, neurological deficits, or viral persistence in semen. Complications include secondary infections, organ failure, and long-term immunosuppression.

8.1 Long-Term Outcomes

Survivors may develop chronic arthralgia, cognitive dysfunction, or mental health issues. Viral persistence in semen can lead to sexual transmission.

8.2 Recrudescence

Rare but documented cases of recrudescent disease from persistent viral reservoirs in immune-privileged tissues.

9. SPECIAL CONSIDERATIONS

Pregnancy: Increased risk of maternal mortality and fetal loss. Vaccination is contraindicated in pregnancy unless exposure risk is high. Pediatric cases are rare but severe. Travelers to endemic areas require pre-travel vaccination.

9.1 Pregnancy

Maternal mortality is high due to coagulopathy and hemorrhage. Fetal loss is common. Vaccination is contraindicated in early pregnancy.

9.2 Travelers

Pre-travel vaccination with YF vaccine (live-attenuated 17D strain) is recommended for endemic regions. Post-exposure prophylaxis is limited.

10. KEY POINTS & CLINICAL PEARLS

Filovirids cause severe hemorrhagic fever with high mortality. Early diagnosis and isolation are critical. Monoclonal antibodies improve survival, but supportive care remains the cornerstone. Prevention relies on vaccination, PPE, and outbreak control. Survivors may experience long-term sequelae and viral persistence.