• small size
• naked (no envelope) icosahedrons
• spherical shape
• protein shell surrounding naked RNA
• ssRNA
• + polarity
• six families
  • aphthoviruses
  • cardiovirus
  • enterovirus
  • hepatovirus (hep A)
  • parechovirus
  • rhinovirus

• required for infection at the cellular level
• the host cell membrane proteins serve as receptors

1. penetration, uncoating, and release of + strand RNA in cytoplasm occurs in minutes
2. RNA will act as monocistronic messanger
3. product is large polyprotein that is cleaved in a series of steps
4. produces 4 capsid proteins
5. progeny RNA are copied from genome via negative strand RNA intermediary and encapsidated
6. host protein and RNA synthesis are completed within 3 hrs of infection, and cell lysis occurs within 8 hrs, with release of progeny viruses

• survive sewage tx plants
• highly stable and resistant to heat, acid pH, chlorine, bile salts, lipid solvents
• transmission via fecal oral transmission and inhalation

• enterioviruses
  • nonpolio enteroviruses
    • coxsackievirus A
    • coxsackievirus B
    • echoviruses
    • enteroviruses
  • poliovirus
• rhinovirus
• hep A

• acquired via ingestion of virus shed in feces or URT or direct and indirect contact
• replicate in URT or distal small bowel (ileum)
• replication in ileal lymphoid tissue with fecal shedding for 6 weeks or longer
• much greater density in GI tract
• viral replication in gut lymphoid tissue gives rise to transient viremia
  • when they get into reticuloendothelial system (major viremia)
• major viremia target organs are CNS (meningitis), heart (myocardiitis), and skin (viral exanthem)
• protective immunity is serotype specific
• importance of neutralizing Ab's (IgG and secretory IgA)

• highest rate of infection in summer and early fall
• highest in northern US and Canada
• infants and young children have highest rates of infection and disease
• higher in low socioeconomic groups (crowding)
• many adults have Ab to more common enterovirus serotypes

• asymptomatic
• nonspecific acute febrile illness (irritability, lethargy, poor feeding, vomitting, diarrhea)
• exanthems and enanthems
  • rash resembles measles, rubella
  • hand foot and mouth disease (cox A)
• CNS infection
  • aseptic meningitis
  • encephalitis
• cardiac and skeletal muscle
  • pleurodynia
  • myositis
  • myopericarditis
• acute hemorrhagic conjunctivitis
• perinatal infections

• dx
  • viral isolation of cell culture
    • primate cell lines
    • CSF, pericardial fluid, tissue, blood
  • PCR- CSF, resp. secretion, cardiac tissue
  • serology (serum IgM)
• tx
  • IV Ig
  • Pieconaril

1. humans only natural host and transmitted via fecal oral route
2. replicates in pharynx and LRT
3. similar to enteroviruses (minor and major viremia)
4. CNS is seeded in 1% infections as result of major viremia
5. viral replication in anterior horn cells of spinal cord
6. neurons in nuclei of medulla, cerebellum, midbrain, hypothalmus
7. neuronal destruction, some reversibility

• infection of CNS
  • anterior horn infection leads to spinal poliomyelitis
  • medullar and brain stem infection leads to bulbar poliomyelitis
  • cortex infection leads to encephalitic poliomyelitis
  • perivascular cuffing of brain stem by monocytes

This causes paralysis

• most of the time asymptomatic or minimal symptoms (flu like)
• rare aseptic meningitis with complete recovery in 5-10 days
• rarely, parlytic polio
  • biphasic
  • initial self resolving minor illness
  • high fever with intense muscle pain
  • decrease, loss reflexes
  • appearance of paralysis is sudden
  • complete loss of motor function in one or more extremities over several hrs
  • max loss within 4 days with improvement over next 6 mnths
  • some have residual deficits
  • hypoxia (due to weakness of diaphragm and intercostal muscles)
    • involve resp. center in brainstem
    • infect CN 9, 10, 12
    • accounts for most deaths with polio

• summer, fall in temperate climates (water activities)
• year round in tropical areas
• pre industrial revolution- endemic form and infected infants early in life (protected by maternal Ab's)
• improved hygiene in early 20th century
  • epidemics appeared
  • lack of contact with virus by youngest population
  • older children and adults become susceptible
• intro of vaccine in 1955 lead to sharp decline

• increase in serum IgM
• increase in duodenal IgA
• increase in serum and nasal IgA

• increase serum IgM
• increase serum IgA

• after interval of 15-40 yrs
• late manifestation of acute paralytic polio
• some who contract paralytic polio in childhood experience muscle pain and exacerbation of paralysis
• factors that enhanced the risk of post polio syndrome
  • increase length of time since acute poliovirus infection
  • presence of permanent residual impairment after recovery of acute illness
  • female gender
• not a consequence of peristent infection
• late attrition of oversized motor units that developed in the recovery process

• cause of common cold
• replicates in respiratory tract epithelium of nose and nasopharynx
• virus replicate at 33-35 degree C (aka lower temps, so this is why its seen in colder months)
• many serotypes
• transmission via aerosol or direct contact
  • virus must be deposited on nasal mucosa
  • virus can be recovered from hands of infected individuals and objects handled by infected persons
  • sneezing and coughing is inefficient

gastroenteritis

Hep E (shared properties with caliciviruses)

• carrier, possibly assymptomatic
  • poor hygeine by food handling
  • undercooked shellfish
  • contaiminated water
• epidemiology
  • ocean liners
  • military camps, jails (crowding)