Filoviruses Notes

Contents

Osmosis High-Yield Notes

This Osmosis High-Yield Note provides an overview of Filoviruses essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Filoviruses by visiting the associated Learn Page.
NOTES NOTES FILOVIRUSES MICROBE OVERVIEW Genetic material ▪ Single-stranded negative-sense RNA virus family; causes viral hemorrhagic fever Taxonomy ▪ Genera: Ebolavirus, Marburgvirus, Cuevavirus Morphology ▪ Enveloped virions; filamentous, nonsegmented morphology Replication ▪ Transcription, replication mediated by virus-encoded polymerase in infected cell cytoplasm ▫ Transcription: negative-sense RNA genome transcribed into monocistronic, polyadenylated RNA species using host cell ribosomes, tRNA etc. → translated into seven proteins ▫ Replication: positive-sense antigenome serves as template for negative-sense genomes Transmission ▪ Zoonotic infection ▫ Natural host: unknown (bats, especially fruit bats considered infection source) ▫ Intermediate host: Often nonhuman primates (gorillas, chimpanzees) Structural proteins ▪ Viral RNA encodes seven structural proteins ▫ Nucleoprotein ▫ Polymerase cofactor (VP35) ▫ Viral proteins VP40, VP24 ▫ Glycoprotein: projecting spikes from lipid bilayer (attachment to host cell receptors) ▫ Transcription activator ▫ RNA-dependent RNA polymerase EBOLA VIRUS osms.it/ebola-virus PATHOLOGY & CAUSES ▪ Ebola virus: causative agent of severe, often fatal hemorrhagic fever ▪ Species: Zaire, Sudan, Tai Forest, Bundibugyo, Reston ▪ Transmission ▫ Animal-human: direct infected-animal tissue, body-fluid contact; butchering, consuming undercooked meat 388 OSMOSIS.ORG ▫ Human-human: direct tissue, body fluid contact with ill/deceased ▫ Potential transmission: contaminated surface/object contact PATHOLOGY ▪ Inoculation → incubation: 6–12 days average (ranges 2–21 days) ▫ Host cell attachment, virus endocytosis → nucleocapsid release in cytoplasm →
Chapter 72 Filoviruses ▪ ▪ ▪ ▪ replication → nucleocapsid formation → viral shedding, cell necrosis Initially macrophages, dendritic cells infected → sentinel lymph node spread → bloodstream → many cell types infected (endothelial cells, fibroblasts, hepatocytes, epithelial cells, adrenal-gland cells) with lymphocyte/neuron exception ▫ Although uninfected, inflammatory mediators; support signal loss from dendritic cells → “bystander” apoptosis of lymphocytes Multifocal necrosis in various tissues (e.g. liver, spleen) Systemic inflammatory syndrome: proinflammatory mediator, cytokine release from infected macrophages, dendritic cells, necrotic cell breakdown products, etc. → vasodilation, ↑ vascular permeability → vascular leakage, shock, multiorgan failure Dendritic cell dysfunction, “bystander” lymphocyte apoptosis → impaired adaptive immunity ▪ Spontaneous abortion, vaginal bleeding in infected pregnant individuals (100% third trimester maternal, fetal mortality) ▪ Fatality ranges ▫ 40% to 80–90% (depending upon species) RISK FACTORS ▪ Healthcare workers without appropriate protective equipment, adequate training ▪ Inadequate infected waste product, corpse handling ▪ Sexual intercourse with person recovering from Ebola in previous three months ▪ Travel to endemic/Ebola epidemic areas ▪ Wild animal contact (mostly nonhuman primates) COMPLICATIONS ▪ Gastrointestinal dysfunction ▫ Fluid loss, hypotension, acute kidney injury, shock ▪ Neurologic ▫ Meningoencephalitis, meningitis ▪ Coagulopathy ▫ Infected macrophages produce tissue factor (TF), stimulate extrinsic coagulation pathway → disseminated intravascular coagulation (DIC) ▪ Respiratory failure ▪ Coinfection/superinfection ▪ Impaired adaptive immunity → bacterial sepsis Figure 72.1 A scanning electron micrograph of an ebola virus demonstrating the typical filamentous structure seen in its class, Filoviridae. SIGNS & SYMPTOMS Initial nonspecific symptoms ▪ Fever, chills, fatigue, headache, appetite loss, malaise, sore throat, myalgias, lumbosacral pain Dermatological ▪ Diffuse erythematous; nonpruritic maculopapular/morbilliform rash, especially on torso/face Gastrointestinal ▪ Watery diarrhea (up to 10L/2.2gal); nausea; vomiting; epigastric, abdominal pain; abdominal tenderness OSMOSIS.ORG 389
Hemorrhage ▪ Commonly hematochezia, followed by hematemesis, melena, metrorrhagia, purpura, petechiae, ecchymoses, mucosal bleeding, venipuncture site bleeding ▫ Often occur later in disease course; not all infected individuals develop significant bleeding; host susceptibilitydependent (genetically determined viral immune response difference), different species’ pathogenicity Neurologic ▪ Meningoencephalitis symptoms (altered level of consciousness, hyperreflexia, myopathy, stiff neck, gait instability, seizure) Ocular ▪ Conjunctival injection, uveitis symptoms (blurred vision, photophobia, blindness) Respiratory ▪ Tachypnea, dyspnea Convalescent period ▪ Can persist > two years often followed by symptoms such as arthralgia, blurred vision, retro-orbital pain, hearing loss, alopecia, difficulty swallowing, insomnia ▪ Infectious virus/viral RNA can persist in body fluid (semen, breast milk, urine, cerebrospinal fluid, aqueous humor) < nine months after not detectable in blood → variable transmission risk DIAGNOSIS ▪ Diagnostic criteria ▫ Clinical manifestation ▫ Travel to endemic/Ebola epidemic areas (within three weeks prior to disease onset) ▫ Infected individual contact during acute disease LAB RESULTS ▪ Reverse-transcription polymerase chain reaction (RT-PCR) ▫ Detectable Ebola virus in blood samples within three days after symptom onset ▪ Rapid chromatographic immunoassay (ReEBOV) 390 OSMOSIS.ORG ▪ Laboratory findings ▫ Leukopenia; thrombocytopenia; ↑ ↓ hematocrit; ↑ aspartate aminotransferase (AST), alanine aminotransferase (ALT) ▫ Prolonged prothrombin (PT), partial thromboplastin time (PTT) ▫ Proteinuria, ↑ blood urea nitrogen, ↑ creatinine ▫ Hyponatremia, hypocalcemia, hyperkalemia TREATMENT ▪ No cure ▪ Infected individual isolation; placement in negative airflow room advised MEDICATIONS ▪ Complications treatment ▫ Coinfection/superinfection: empiric antimicrobial therapy with broad spectrum antibiotics ▫ Shock: intravenous fluids, vasoconstrictors ▫ Fever reduction: antipyretic agents OTHER INTERVENTIONS ▪ Complications treatment ▫ Fluid, electrolyte loss correction ▫ Acute kidney injury: renal replacement therapy (dialysis) ▫ Respiratory failure: supplemental oxygen therapy, mechanical ventilation (if necessary, barotrauma risk)

Osmosis High-Yield Notes

This Osmosis High-Yield Note provides an overview of Filoviruses essentials. All Osmosis Notes are clearly laid-out and contain striking images, tables, and diagrams to help visual learners understand complex topics quickly and efficiently. Find more information about Filoviruses by visiting the associated Learn Page.