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The Filovirids: Orthoebolavirus and Orthomarburgvirus Infections

Chapter 216 | Part 5: Infectious Diseases · Part 5 – Infectious Diseases: Viral (incl. HIV) · Chapter 216

Key Clinical Points

  1. Filovirid disease (FVD) is a WHO Risk Group 4 pathogen requiring biosafety level 4 containment.
  2. Incubation period: 2–25 days (most commonly 7–10 days).
  3. Case-fatality rate: 44.6% overall; 65.2% for Marburg; historically 70–90% for EBOV.
  4. Two FDA-approved monoclonal antibody therapeutics for EBOV: ansuvimab-zykl (mAb114) and atoltivimab/maftivimab/odesivimab-ebgn (REG-EB3).
  5. Primary reservoirs include Egyptian rousette bats; hunting bushmeat is a major exposure risk.
  6. Differential diagnosis includes malaria, typhoid, EHEC, gram-negative septicemia, and other viral hemorrhagic fevers like Lassa or yellow fever.
  7. Diagnosis requires RT-PCR targeting filovirid genes with a detection limit of 1000–5000 PFU/mL serum.
  8. Treatment involves supportive care plus mAb therapy for EBOV; no approved therapeutics exist for other filovirids.
  9. Persistent infection in immune-privileged tissues (CNS, reproductive tract, eyes) can lead to outbreak reignition.
  10. Vaccination with 17D vaccine provides immunity within 10 days lasting 25–35 years; contraindicated in children <6 months.

1. DEFINITION & OVERVIEW

Filovirid disease (FVD) is a severe viral infection caused by viruses in the family Filoviridae. FVD is subdivided into Ebola disease (EBOD; ICD-11, code 1D60.0) and Marburg disease (MARD; ICD-11, code 1D60.1). FVD is categorized as WHO Risk Group 4 pathogens requiring maximum containment (biosafety level 4) laboratories.

Human-to-human transmission occurs through direct person-to-person contact or exposure to infected bodily fluids or tissues; there is no evidence of aerosol or respiratory droplet transmission in natural outbreak settings.

1.1 Classification & Taxonomy

• Family Filoviridae: contains nine official genera. • Human Pathogens: found in two genera: ◦ Orthoebolavirus (causes EBOD; includes BDBV, EBOV, SUDV, TAFV) ◦ Orthomarburgvirus (causes MARD; includes Marburg virus and Ravn virus) • Naming Convention: Specific diseases are optimally named with virus-specific cause (e.g., EVD distinguished from Sudan virus disease [SVD]).

1.2 Virus Structure & Genome

• Genome: linear, nonsegmented, negative-sense RNA approximately 19 kb in length. • Genes: seven genes encoding structural proteins (NP, VP35, VP40, GP, VP30, VP24, L protein). • Orthoebolaviruses: encode three nonstructural proteins (sGP, ssGP, \Delta-peptide). • Morphology: Filovirions are pleomorphic filaments; width ≈ 91–98 nm; average length < 1 μm.

1.3 WHO Risk Group Classification

• Requirement: All work with material potentially containing replicating filovirids must be conducted in BSL-4 laboratories. • Personnel: Must be experienced, use appropriate PPE, and follow standard operating procedures. • Reporting: Notify national authorities and WHO reference labs immediately if outbreaks are suspected.

2. EPIDEMIOLOGY

The majority of recorded FVD outbreaks can be traced back to single index patients. As of November 13, 2024, 35,608 cases and 15,886 deaths had been recorded globally. The 2013–2016 EVD outbreak in Western Africa was the largest with 28,652 cases and 11,325 deaths.

• Case-fatality rate (CFR): ◦ Overall: 44.6% ◦ Marburg: 65.2% ◦ EVD (historical): 70–90%. • Influencing Factors: virus type, reservoir hosts, human population susceptibility, and geographic setting. • Table 1 — Filovirid Disease Outbreak Statistics (as of November 13, 2024): ◦ All Orthoebolavirus: 28,652 cases; 11,325 deaths; 44.6% CFR ◦ All Orthomarburgvirus: 7,000 cases; 4,563 deaths; 65.2% CFR ◦ All Filovirids: 35,608 cases; 15,886 deaths; 44.6% CFR

2.2 Geographic Distribution

• Endemic Regions: equatorial Africa (Western, Middle, Eastern). • EVD Links: bushmeat hunting and forest contact. • Marburg Links: cave exposure in arid woodlands. • Reservoirs: Egyptian rousette bats are natural reservoirs for both Marburg virus and Ravn virus.

2.3 Reservoir Hosts

• EBOV & Reston: linked to frugivorous/insectivorous bats via antibody detection. • BDBV, SUDV, TAFV: hosts remain enigmatic. • Bombali virus: only orthoebolavirus with complete genome detected in bats. • Containment Strategy: limit high-risk activities (e.g., burial practices).

3. ETIOLOGY & PATHOPHYSIOLOGY

Human infections occur via direct exposure to contaminated body fluids or parenteral inoculation. GP spikes determine cell tropism by engaging NPC1 receptor. Filovirids modulate immune responses through structural proteins (VP35, VP40, VP24) that suppress interferon pathways.

3.1 Immune Modulation Mechanisms

• Target Cells: macrophages, monocytes, dendritic cells. • Interferon Inhibition: structural proteins inhibit type I interferon antiviral pathways. • Cytokine Response: infected macrophages secrete proinflammatory cytokines. • Dendritic Cell Impact: activation suppressed with reduced MHC II expression. • Lymphoid Depletion: occurs in lymph nodes, spleen, and thymus.

3.2 Coagulopathy & Endothelial Dysfunction

• Laboratory Markers: Thrombocytopenia, increased tissue factor, D-dimers, decreased protein C. • Tissue Impact: Fibrin deposition in gonads, kidneys, spleen. • Clinical Signs: Petechiae, ecchymoses, visceral effusions. • Vascular Effect: Endothelial cell infection leads to increased vascular permeability.

3.3 Lymphoid Depletion

• Severity: Severe lymphopenia due to massive lymphocyte death. • Consequence: Increased susceptibility to secondary infections.

4. CLINICAL FEATURES

Diseases caused by orthoebolaviruses and orthomarburgviruses present similar clinical phenotypes. Incubation period: 2–25 days (7–10 days typical). Clinical course includes prodrome, gastrointestinal symptoms, rash, hemorrhagic manifestations, and multiorgan failure.

4.1 Clinical Course Timeline

• Nonspecific Prodrome: fever, fatigue, anorexia, myalgia, headache. • Gastrointestinal Phase: nausea, vomiting, diarrhea, abdominal pain. • Progression: Rash development → Hemorrhagic manifestations → Hemodynamic instability and shock → Renal/respiratory failure → Neurologic manifestations → Cardiac dysfunction → Hepatic injury → Hypoglycemia/hypoalbuminemia.

4.2 Laboratory Findings

• Leukocytes: Leukopenia (as low as 1000/μl) with left shift prior to leukocytosis. • Platelets: Thrombocytopenia (as low as 50,000/μl). • Liver/Renal: AST (increased, often > ALT), creatinine, urea, proteinuria. • Electrolytes: Hyponatremia, hypokalemia, hypocalcemia, hypomagnesemia. • Metabolic: Hypoglycemia, hypoalbuminemia. • Coagulation: Prolonged PT/PTT. • Inflammation: Elevated CRP and CPK. • Table 2 — Typical Laboratory Findings in Filovirid Disease: ◦ WBCs: \downarrow (leukopenia) as low as 1000/μl ◦ Platelets: \downarrow (thrombocytopenia) as low as 50,000/μl ◦ AST: \uparrow (often > ALT) ◦ Na+: \downarrow (hyponatremia) ◦ K+: \downarrow or \uparrow ◦ Ca2+: \downarrow (hypocalcemia) ◦ Mg2+: \downarrow (hypomagnesemia) ◦ Glucose: \downarrow (hypoglycemia) ◦ Albumin: \downarrow (hypoalbuminemia) ◦ PT/PTT: \uparrow (prolonged) ◦ CRP: \uparrow (markedly elevated in severe disease) ◦ CPK: \uparrow (elevated)

4.3 Clinical Presentation by System

• Gastrointestinal: nausea, vomiting, diarrhea, abdominal pain. • Respiratory: chest pain, cough, dyspnea. • Cardiovascular: hypotension, edema, shock. • Central Nervous: confusion, headache, coma. • Hemorrhagic: subconjunctival injection, petechial rash, gingival bleeding, epistaxis, hematemesis, hematuria, melena, injection site bleeding. • Hepatic: elevated aminotransferases, synthetic dysfunction. • Renal: oliguria, azotemia, albuminuria. • Cardiac: myocarditis, pericarditis.

5. DIFFERENTIAL DIAGNOSIS

Filovirid disease cannot be diagnosed based on clinical presentation alone.

5.1 Primary Infectious Mimics

• Falciparum malaria • Typhoid fever • Enterohemorrhagic E. coli enteritis • Gram-negative septicemia (shigellosis) • Meningococcal septicemia • Rickettsial infections • Fulminant viral hepatitis • Leptospirosis • Measles • Lassa fever • Yellow fever

5.2 Noninfectious Mimics

• Venomous snakebites • Warfarin intoxication • Acquired/inherited coagulopathies

5.3 Exposure History Clues

• Cave/mines exposure • Contact with bats, nonhuman primates, bushmeat • Contact with severely ill local residents • Admission to rural hospitals with patient clusters

6. INVESTIGATIONS & DIAGNOSIS

Laboratory diagnosis requires biosafety level 4 containment. Acute-phase blood/serum is preferred. Diagnostic samples must be collected with appropriate PPE and transported to reference labs.

6.2 Sample Collection & Processing

• Collect acute-phase blood/serum with appropriate PPE. • Inactivate samples in mobile field glove boxes if available. • Transport to national/international reference labs using suitable media.

6.3 Diagnostic Algorithm

  1. Suspect FVD based on epidemiologic and/or clinical manifestations.
  2. Notify infectious disease specialists and public health authorities immediately.
  3. Collect acute-phase blood/serum with appropriate PPE.
  4. Inactivate samples in mobile field glove boxes if available.
  5. Perform RT-PCR targeting filovirid genes (detection limit 1000–5000 PFU/mL).
  6. If positive → send to national/international reference laboratory.
  7. Conduct supportive care and consider mAb therapy for EBOV.
  8. Monitor for clinical improvement and complications.
  9. Implement infection prevention and control measures.
  10. Report to WHO reference laboratories.

7. MANAGEMENT & TREATMENT

Clinical management requires trained healthcare workers using appropriate PPE. FDA-approved monoclonal antibody therapeutics are available for EVD.

7.1 Monoclonal Antibody Therapeutics

• mAb114 (ansuvimab-zykl): single-dose infusion; neutralizes EBOV. • REG-EB3 (atoltivimab/maftivimab/odesivimab-ebgn): single-dose infusion; neutralizes EBOV. • Table 4 — FDA-Approved Monoclonal Antibody Therapeutics for EVD: ◦ Ansuvimab-zykl: Monoclonal antibody; Neutralizes EBOV; Single-dose; Once; Monitor for hypersensitivity. ◦ REG-EB3: Monoclonal antibody combination; Neutralizes EBOV; Single-dose; Once; Monitor for hypersensitivity.

7.2 Supportive Care Measures

  1. Monitor and manage respiratory dysfunction (oxygen).
  2. Manage circulatory dysfunction (fluid repletion, vasopressors).
  3. Address CNS dysfunction (rule out hypoglycemia).
  4. Detect/manage acute kidney injury.
  5. Control hemorrhage.
  6. Correct electrolyte derangements.
  7. Optimize nutrition.
  8. Prevent/treat secondary infections.
  9. Pain management.
  10. Administer antipyretics, antiemetics, and antidiarrheals.

7.3 Critical Strategies for Severely Ill Patients

  1. Prevent organ dysfunction.
  2. Provide temporary organ support (mechanical ventilation, renal replacement).
  3. Expand window for medical countermeasures and immune response development.

7.4 Long-term Care Considerations

  1. Monitor long-term health outcomes for survivors.
  2. Surveillance to prevent relapse/recrudescent syndromes.
  3. Monitor for public health consequences (outbreak reignition).

8. PROGNOSIS & COMPLICATIONS

FVD has poor prognosis with case-fatality rates up to 70–90% historically for EVD. Outcomes depend on virus type, host factors, viral load, and supportive care.

8.1 Case-Fatality Rates by Virus

• Overall: 44.6% • Marburg disease: 65.2% • EVD (historical): 70–90%.

8.2 Long-term Complications

• Persistent infection: in immune-privileged tissues (male reproductive tract, CNS, intraocular). • Outbreak risk: potential for outbreak reignition. • Unknown outcomes: long-term health outcomes for survivors are currently unknown.

8.3 Survivor Surveillance

• Monitoring: Short- and long-term surveillance required. • Recrudescence: Monitor for relapse/recrudescent syndromes. • Public Health: Prevent public health consequences (outbreak reignition).

9. SPECIAL CONSIDERATIONS

Special considerations include pregnancy, pediatric care, biosafety protocols, and endemic area management.

9.1 Pregnancy Considerations

• Limited data on safety of mAb therapies in pregnancy. • Risk of maternal-fetal transmission. • Requirement for multidisciplinary care.

9.2 Pediatric Considerations

• Higher case-fatality rates in children. • Unique supportive care needs. • Limited data on mAb efficacy in pediatric populations.

9.3 Biosafety & Infection Control

• All filovirid work requires BSL-4 containment. • PPE protocols for healthcare workers. • Strict barrier techniques during sample collection.

9.4 Endemic Area Considerations

• Importance of community engagement and education. • Strengthening local healthcare infrastructure. • Training in infection prevention and control.

10. KEY PEARLS & CLINICAL TRAPS

Key pearls include diagnostic clues, clinical traps, and mnemonics for filovirid disease management.

10.1 Diagnostic Clues

• High index of suspicion in equatorial Africa. • Exposure history (caves, bushmeat). • Hemorrhagic manifestations with multiorgan failure.

10.2 Clinical Traps

• Misdiagnosis: as common febrile illnesses. • Delayed diagnosis: leading to nosocomial spread. • Underestimation: of case-fatality rates in non-outbreak settings.

10.3 Mnemonics

• FILVIR: Focus on infection control, Laboratory safety, Viral containment, Infection prevention, Rapid response. • EBOV: Exposure, Bleeding, Organ failure, Viral persistence.