RNA Virus

RNA Virus section provides High Yield Information needed for USMLE, COMLEX, Medical School, Residency, and as a practicing Physician.

Table Of Contents
1 Positive RNA Virus
1.1 Picornavirus
1.1.1 Coxsackievirus
1.1.2 Hepatitis A
1.1.3 Polio Virus
1.1.4 Rhinovirus
1.2 Calicivirus/Norovirus/Norwalk
1.3 Flavivirus Family
1.3.1 Dengue Fever
1.3.2 Hepatitis C
1.3.3 West Nile Virus
1.3.4 Yellow Fever
1.4 Togavirus
1.4.1 Arbovirus
1.4.2 Rubella
1.5 Coronavirus
1.6 Retrovirus: HIV/AIDs
2 Negative RNA Virus
2.1 Orthomyxovirus
2.2 Paramyxovirus
2.2.1 Measles (Rubeola)
2.2.2 Mumps
2.2.3 Respiratory syncytial virus (RSV)
2.2.4 Parainfluenza virus
2.2.5 Rhabdovirus
2.3 Filovirus
2.4 Bunyavirus
2.5 Arenavirus

Positive RNA Virus

Picornavirus

  • Features:
    • RNA virus
    • Positive sense – replicates in cytoplasm
    • Naked envelope
    • Enterovirus
  • Transmission:
    • Fecal oral route
  • Subgroups:
    • – Hepatitis A
    • – Poliovirus
    • – Coxsackie A and B
    • – Echovirus
    • – Rhinovirus- common cold
  • Enteroviruses:
    • Polio, Coxsackie and Echoviruses are main causes of aseptic meningitis
    • – CSF
    • – Elevated proteins
  • Most commonly affects:
    • children
Coxsackievirus
  • Features:
    • Picornavirus- Enterovirus
    • Positive Sense RNA virus (replication in cytoplasm)
    • Naked virus
  • Two types: Coxsackie A and B
    • Coxsackie A:
      • Common in summer months
      • Clinical presentation:
        • – Hand, foot, and mouth disease: red vesicular rash
        • – Aseptic meningitis (common to all enteroviruses)
    • – Coxsackie B:
      • Presentation
        • – Dilated cardiomyopathy
        • – Pleurodynia/Devil’s grip/ Bornholm’s disease
          • extreme sharp chest pain, unilateral pain, causes difficulty of breathing
  • No treatment
    • Supportive therapy only
Hepatitis A
  • Features:
    • Picornavirus
    • Positive sense RNA virus (replicates in cytoplasm)
    • Naked virus
    • Acid stable
  • Transmission:
    • – Fecal orally
    • – Virus sheds in feces and can contaminate water supply
    • – Ingestion of shellfish that was caught in contaminated water
  • Clinical presentation:
    • – Asymptomatic: most of the time
    • – Anicteric/no jaundice
    • – Acute viral hepatitis: fever, jaundice, hepatomegaly
    • – Children: anicteric in young children and infants
    • – Smokers with hepatitis A–> aversion to smoking
  • Treatment and symptom duration:
    • – Duration of illness: 1 month
    • – Self limiting
    • – No carrier/chronic state
  • Prevention:
    • – Vaccination: inactivated/killed vaccine given to those who are at high risk situations
Polio Virus
  • Features:
    • Picornavirus: Enterovirus
    • Positive sense RNA virus (replication in cytoplasm)
    • Naked virus
    • Causes polio
  • Transmission:
    • – fecal-oral
    • – Virus replicates in lymphoid tissues of GIT
  • Presentation:
    • – Asymmetric paralysis within 2-3 weeks after infection
    • – Myalgias
    • – Decreased DTR
    • – Respiratory insufficiency: paralysis ascends to diaphragm–> Most common cause of death in polio infected patients
    • – Aseptic meningitis All enteroviruses can cause aseptic meningitis
  • No treatment
  • Prevention: Vaccine
    • – Salk and Sabin
    • – Salk: inactivated/killed vaccine through injection
    • – Sabin: live attenuated vaccine given orally
Rhinovirus

Calicivirus/Norovirus/Norwalk

  • Features:
    • Single strand RNA positive sense (replicates in cytoplasm)
    • Naked virus
    • Most common type of Calicivirus: Norovirus/Norwalk virus
  • Outbreak: people in close quarters
    • – Cruise ships-
      • Norovirus/Norwalk virus responsible for >90% of diarrheal illness outbreaks on cruise ships
    • – Day care centers and school
  • Transmission:
    • – Consumption of shellfish: especially raw shellfish
  • Clinical Presentation:
    • – Viral gastroenteritis: diarrheal illness- explosive watery diarrhea

Flavivirus Family

Dengue Fever
  • Features:
    • Flavivirus
    • RNA positive sense virus
    • Enveloped
    • Non-segmented RNA
  • Transmission:
    • – Aedes Egyptei mosquito
    • Infects bone marrow “break bone fever”
  • 4 serotypes of dengue: most common: type 2
    • Hemorrhagic type of fever
  • Clinical manifestation:
    • – Thrombocytopenia: virus infects bone marrow–> increase risk of bleeding
    • – Renal failure
    • – Septic shock
    • – Death
  • Treatment:
    • – Supportive
    • – Make sure patient is well hydrated
Hepatitis C
  • Features:
    • Flavivirus
    • RNA positive sense virus
    • Enveloped
    • Non-segmented
  • Transmission:
    • – Exposure to infected blood
    • – IV drug users: needle sharing
    • – Placenta
    • – Sex (Hep B > Hep C)
    • – Breast feeding
    • – Very infectious virus
  • Clinical presentation:
    • – Inflammation to liver/hepatitis
    • – Acute inflammation:
    • Jaundice
    • Right upper quadrant pain
    • Hepatomegaly
    • Increased liver enzymes
    • 60-80% acute infections will become chronic hepatitis
    • Lymphocytes infiltrate portal tract and with the chronic inflammation and infection hepatocytes die
  • Chronic infection:
    • – Cirrhosis
    • – Increase risk of HCC
  • Acute infection:
    • – Hep C RNA in serum during first 6 months
    • – ALT will rise and fall by 6 months
    • – Resolved infections: anti-HCV antibody will rise within 2-3 months
  • Chronic infection:
    • – Hep C RNA persists in serum after 6 months
    • – Biopsy of liver: lots of lymphocytes in portal tract
    • HepC is associated with cryoglobulins: serum proteins containing Ig mostly IgM precipitates out in cold temperatures
  • Treatment:
    • – protease inhibitors
    • – polymerase inhibitor
    • – genotype testing: needed to determine combination of drugs to be used
    • – Hep C is the leading cause of liver transplant
West Nile Virus
Yellow Fever

Togavirus

Arbovirus
  • Features:
    • Togavirus family
    • RNA positive sense virus
    • Enveloped
    • “Arthropod born virus”
  • Vector:
    • mosquito
    • Different types of arbovirus
      • – Western Equine encephalitis: Western US
      • – Eastern Equine Encephalitis: Eastern US
      • – Venezuelan Equine Encephalitis: Southern and central America
  • Clinical presentation:
    • – Encephalitis
    • – Headache
    • – Fever
    • – Altered mental status
    • – Focal neural deficits
  • No treatment
  • Prevention:
    • – Protective clothing
    • – Netting
    • – Bug spray
Rubella
  • Features:
    • Togavirus
    • RNA positive sense virus
    • Enveloped
  • Transmission:
    • Respiratory droplets
  • Causes: 
    • “German measles”
    • Exanthem in children
    • 3 Presentations for 3 Different age groups
      • – Congenital rubella
      • – Rubella in children
      • – Rubella in adults
    • Childhood rubella
      • – Tender post-auricular and occipital LAD
      • – Maculopapular rash that begins in face and moves downwards
      • – Prodrone: Mild fever, LAD, fatigue
    • Rash of rubella moves faster than rubeola/measles
    • Rash doesn’t darken or coalesce
    • Congenital Rubella
      • – Part of TORCHeS: crosses placental and affects fetus in utero
    • Constellation of symptoms:
      • – Mental retardation
      • – Microcephaly
      • – Blindness
      • – Deafness
      • – Cataracts
      • – Jaundice
      • – PDA
      • – Pulmonic stenosis
      • – Pruritic blueberry muffin rash
      • – Radiolucent bone lesions
    • Triad:
      • – Congenital cataracts
      • – Sensory neural deafness
      • – PDA
    • Adult Rubella
      • – LAD
      • – Fever
      • – Arthralgia
      • – Arthritis
  • No treatment
  • Vaccine:
    • MMR vaccine
    • – live attenuated vaccine
    • *Not given to pregnant or immunocompromised patients

Coronavirus

  • Features:
    • RNA positive sense virus
    • Encapsulated: helical shaped
  • Causes:
    • – SARS
    • – Common cold (like rhinovirus)
  • Clinical presentation:
    • – Acute bronchitis that can lead to acute respiratory distress syndrome/ARDS
  • Diagnosis of SARS:
    • – Test for Ab with SARS
    • – Confirm with PCR
  • Clinically:
    • negative finding if absent Ab over 28 days
  • Treatment:
    • – Broad spectrum antibiotics
    • – Ribavirin
    • – Corticosteroids
    • – Efficacy is variable

Retrovirus: HIV/AIDs

  • Features:
    • ssRNA positive sense virus that is converted by a DNA intermediate via reverse transcriptase enzyme
    • Enveloped
    • Diploid RNA positive virus
  • 3 important genes used for replication:
    • – gag – p24 serves as capsule for RNA strands
    • – env – responsible for making gp41 and gp120 – used to form viral envelope
    • env makes gp160–> gp120 and gp41
    • – pol – polymerase: reverse transcriptase to convert RNA-> DNA
  • Transmission:
    • – Primarily sexual contact
    • – Vertical transmission
    • – Blood
    • – Part of TORCHeS infection
    • HIV infects macrophages
    • HIV targets macrophages and helper T cells
    • Progression of virus
      • – Primary/prodrome
  • Causes: 
    • – Flu/mono like symptoms with cervical LAD
    • – Fever lasting for several weeks
    • – Self limiting
    • – Latent period
    • – Can last up to 10 years
    • – Virus replicates in LNs
    • – AIDS
    • <200 CD4+ Cells
  • Infection:
    • – virus binds to CCR5 and CXCR4 co receptors on host cells
  • Diagnosis:
    • – ELISA test
    • – Western blot/gel electrophoresis = CONFIRMATION TEST
  • Treatment:
    • Anti-retroviral therapy:
      • – NRTI: Zidovudine
      • – NNRTI
      • – Protease inhibitors
      • – CCR5 inhibitor
      • Combination therapy- better than monotherapy

Negative RNA Virus

Orthomyxovirus

  • Features:
    • ssRNA negative virus
    • – Negative virus: needs to be transcribed to positive strand–> virus brings its own RNA polymerase
    • Only RNA virus replicated in Nucleus
    • Enveloped
  • Most important virus: 
    • Influenza virus: 3 strains
      • – A: most important causes epidemic and pandemic. Antigenic shift and antigenic drift
      • – B: causes endemics: antigenic drift
  • Key features of orthomyxovirus:
    • – Replicates in nucleus (only RNA)
    • – Segmented virus (8 segments)
    • – Hemaglutinin/HA
    • Glycoprotein on surface of influenza virus binds to sialyc acid on membranes of respiratory tract or RBC
  • Transmission:
    • – HA molecule binds to sialic acid on cell membrane
    • – Virus endocytosed in cell
    • – Virus replicates in nucleus
    • – NA/neuraminidase: cleaves sialic acid to release newly formed virions from host cells
    • – Respiratory droplets
  • Commonly seen during: December- February
  • Clinical presentation:
    • – Myalgia
    • – Fever
    • – Non- productive cough for 7 days
  • Complications:
    • Resolution-> productive cough and fever
    • – Pneumonia
    • – Post viral bacterial pneumonia infection: Staph aureus or Strep pneumonia
    • Aspirin
    • – Contraindicated in children with flu like syndrome
    • – Increase risk of reye’s syndrome
  • Associated with:
    • Guillain Barre Syndrome
  • Vaccines:
    • – Live attenuated nasal spray
    • – Killed injectable
    • trivalent
    • quadrivalent

Paramyxovirus

Measles (Rubeola)
  • Features:
    • Paramyxovirus
    • ssRNA negative sense (replicates in cytoplasm)
    • Enveloped virus
  • Transmission:
    • Respiratory droplets
  • Virulence factors:
    • – HA
    • – Fusion proteins
  • Clinical presentation:
    • – Prodrone/3 C’s
      • – cough
      • – conjunctivitis
      • – coryza
      • – Koplik spots
    • – Fever >104F lasting 4 days
    • – After 1-2 days of koplik spots–> maculopapular rash appears: starts on back of ears–> neck and face–> downward
    • itchy maculopapular rash, starts small then blends together
  • Complications:
    • – Viral or bacterial pneumonia
    • – SSPE/Subacute sclerosing panencephalitis – 5-10 years after measles infection
  • Treatment:
    • Vitamin A- Reduces morbidity and mortality
Mumps
Respiratory syncytial virus (RSV)
  • Features:
    • Paramyxovirus
    • ssRNA negative virus
    • Enveloped
    • Seen in infants <6 months
    • Infects cells by attaching to respiratory endothelium through G protein
  • Infection causes:
    • – Bronchiolitis
    • – Pneumonia
    • – Rhinitis
    • – Pharyngitis
  • Most common cause of:
    • pneumonia and bronchiolitis in infants
  • Virulence factors:
    • – Fusion protein
  • Treatment:
    • – Ribavirin- for adults
    • – Palivizumab- for children in high risk
Parainfluenza virus
Rhabdovirus
  • Features:
    • ssRNA negative sense virus
    • Enveloped: bullet shape
    • Helical nuclear capsid
    • Zoonotic virus
  • Carriers in US:
    • – Bats
    • – Squirrels
    • – Skunks
    • – Foxes
    • – Raccoons
  • Causes:
    • Rabies
  • Virulence Factor:
    • – Glycoprotein binds to nicotinic ACh receptors in post synaptic membrane of NMJ
      • Virus travels retrograde via PNS–> Dorsal root ganglia
  • Clinical presentation:
    • – increase salivation
    • – spasms and excruciating pain in the muscles of the throat and neck
    • – high fever
    • – encephalitis
    • – neuronal death
    • – death
  • Diagnosis:
    • – History: positive history of exposure
    • – Confirmatory Dx: biopsy or autopsy of the presence of Negeri bodies
  • Treatment:
    • – Passive Immunization with human rabies Ig
    • – Active immunization with killed vaccine
    • – Post exposure antibody

Filovirus

  • Features:
    • ssRNA negative sense virus
    • Enveloped
    • Helical capsid
    • Causes Ebola
  • Clinical presentation:
    • – Signs of hemorrhagic fever: sweating and fever
    • – Rashes: petechial rash
    • Symptoms occur days to weeks after obtaining virus
    • Causes end organ failure–> death ( hypovolemic shock)
  • At risk:
    • – Direct contact with animal with the virus: monkeys and bats in endemic areas
    • – Healthcare workers who treat infected individuals- transmission through bodily fluids

Bunyavirus

  • Features:
    • ssRNA negative sense virus
    • Enveloped
    • Segmented: 3 segments
    • Most bunyavirus are arboviruses: arthropod borne
  • Huntavirus:
    • – Most important bunyavirus
  • Transmission:
    • contact with rodents and their excrement
  • Clinical presentation:
    • Pulmonary edema and Hemorrhagic fever
  • Types of bunyaviruses:
    • – Rift Valley fever- aedes mosquito
    • – California encephalitis – aedes mosquito
  • Clinical manifestations:
    • – Non fatal: causes neurologic problems
    • – Seizure
    • – Encephalitis
    • – Myalgia
    • – Fever

Arenavirus

  • Features:
    • ssRNA negative sense viruse
    • Enveloped
    • Helical shaped nucleocapsid
    • *Capacity to encode both negatively and positively sense RNA
    • – Ambisense
    • Segmented virus: 2 segments
    • Associated with rodent transmitted diseases in humans
  • Causes:
    • – Lymphocytic choriomeningitis virus
  • Clinical presentation:
    • – Fever
    • – aseptic meningoencephalitis
  • Diagnosis:
    • Electron microscopy: sandy- granular outer capsid
  • Inactivated by:
    • – Heating
    • – Radiation
    • – Low pH
    • – Detergents