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• What is viral infection not synonymous with?

  Disease
• What are subclinical viral infections also known as?

  Asymptomatic or inapparent
• How is virulence defined in relation to viruses?

  As a measure of pathogenicity
• What must viruses do to cause disease?

  Infect, spread, and damage tissues
• How must viruses be shed to infect another host?

  In secretions or excretions
• What is required for virus propagation?

  Transmission to another susceptible host
• How do viruses differ in their virulence?

  They vary greatly among species
• What factors contribute to differences in infection outcomes among animals?

  Variation in viral virulence and host factors
• What contributes to viral virulence?

  Often multigenic determinants
• What are determinants of host resistance/susceptibility?

  Multifactorial factors including host and environment
• How has molecular technology impacted the study of viral virulence?

  It allows mapping of virulence determinants
• What are the differences in virus strain characteristics?

  • Rate/yield of virus replication
  • Lethal dose
  • Infectious dose
  • Number of cells infected
  • Organ or tissue tropism
  • Extent of host-cell damage
  • Mode and efficacy of spread
  • Character of the disease induced
• What factors must be equal when comparing viral virulence?

  Infecting dose, age, sex, condition, immune status
• What does LD50 stand for?

  Lethal dose 50
• What does ID50 represent?

  Infectious dose causing infection in 50%
• What were the ID50 and LD50 for BALB/c mice infected with ectromelia virus?

  ID50: 2 virions; LD50: 5 virions
• How can viral virulence be assessed?

  By ability to cause disease or lesions
• What has molecular biology facilitated in terms of viral virulence?

  Determination of genetic basis of virulence
• Why are viral infections less pathogenic in natural hosts?

  Natural hosts have evolved resistance
• What determines host resistance to a virus?

  Expression of critical receptors on target cells
• What is the significance of conserved receptors in viral infections?

  They allow a wider host range
• What change can lead to the emergence of variant viruses?

  Changes in viral attachment mechanisms
• How do enteric viruses typically infect the gastrointestinal tract?

  By ingestion of contaminated food or drink
• What protects the gastrointestinal tract from viral infections?

  Acidity, mucus, and immune mechanisms
• Where do enteric viruses typically first infect?

  Epithelial cells lining the GI mucosa
• What is the role of the skin in viral infections?

  It provides a mechanical barrier
• What can predispose the skin to viral infections?

  Breaches in skin integrity
• How can arthropods contribute to viral infections?

  As mechanical or biological vectors
• How do some viruses enter through the conjunctiva?

  By overcoming mechanical cleansing mechanisms
• What challenges do viruses face during multisystemic spread?

  Immune system disruptions and cell type infection
• How do some viruses disseminate after initial infection?

  Through lymph and bloodstream
• What is essential for virus adsorption to cells?

  Proper receptor sites on cell surfaces
• What are some pathological changes caused by viruses?

  Vacuolation, hypertrophy, and syncytium formation
• What are inclusion bodies?

  Abnormal structures formed during viral infection
• What are Negri bodies a sign of?

  Rabies infection

  
• Where are Negri bodies often found?

  In Purkinje cells of the cerebellar cortex