4th exam part 1

Viral Epidemiology

• Viruses reproduce within host cells—either productively or latently.
• Productive infection leads to the production of more viruses and cell lysis, releasing the virions.
• Latent infection involves the viral genome becoming part of the host cell's DNA, replicating as a plasmid.
• Viral infectiousness often categorized by transmission route.

Classification of Animal Viruses

• Enteric viruses are typically transmitted via the fecal-oral route and often cause gastroenteritis.
• Respiratory viruses spread through inhaled infected respiratory droplets, commonly remaining localized in the respiratory tract.
• Zoonotic viruses spread from animals to humans through animal vectors.
• Sexually transmitted viruses can cause genital lesions or systemic infections.

Interactions of Animal Viruses with Their Host

• The outcome of viral infection depends on factors independent of the host's cell defense mechanisms.
• Viruses can establish balanced pathogenicity with the host, causing no obvious disease or damage.
• Acute infection is characterized by a brief duration, potential for long-lasting immunity, and the production of large numbers of viruses.
  • Disease symptoms arise from tissue damage, infection of new cells, and viral reproduction.
  • Viral reproduction cycle is similar to virulent bacteriophages, with steps including attachment, entry, targeting reproduction sites, uncoating, nucleic acid replication, protein coat removal, maturation, cell lysis and spreading through host.
• Persistent infections are characterized by the continuous presence of the virus in the host. These infections can be categorized as latent, chronic, or slow.
  • Latent infections involve a period of dormancy, the virus typically lying dormant in the host until reactivation.
  • Chronic infections involve the continuous presence of the infectious virus in the host throughout the infection period. Presence of disease symptoms can be present or absent during the infection.
  • Slow infections are characterized by a gradual increase in the amount of infectious agent, with a long asymptomatic period before symptoms become significant.

Epidemiology Tools

• Notifiable diseases are tracked through national surveillance systems like the CDC.
• Active and passive surveillance methods involve systematic surveys of populations and disease presence. Active surveillance establishes sentinel sites and observes animals and vectors.