PATHOGENESIS OF VIRAL INFECTIONS AND DISEASES Flashcards
Not synonymous with disease (there are some subclinical viral infections : asymptomatic, inapparent)
VIRAL INFECTION
Used as a quantitative or relative measure of the pathogenicity of the infecting virus
VIRULENCE
What are the viruses to cause disease?
Infect their host
Spread within the host damage target issues
Must be transmitted to another susceptible host
Virus propagation
Quantitative Virus strain differences
Rate yield of the virus replication (Lethal dose & Infectious dose).
Number of cell infected in an organ.
Qualitative Virus strain differences
Organ or tissue tropism
Extent of host-cell damage
Mode and efficacy of spread in the body
Character of the disease they induce
dose of the virus required to cause death in 50% of animals
LD50 or Lethal dose 50
Ratio of the dose of a virus that causes infection in 50% of individuals
ID 50 or Infectious dose 50
Viral virulence can also be estimated through the assessment of:
Severity of an infection
Location
Distribution of gross, histological and ultrastructural lesions in affected animals.
tend to be less pathogenic in their natural host species than in exotic or introduced species.
VIRAL INFECTIONS
True or False :
More conserved or ubiquitous receptors = wider host
True
Mechanisms of viral infections and virus dissemination
Via respiratory tract
Via gastrointestinal tract
Via skin
other routes: Genital tract, conjuctiva
Via the respiratory tract
MUCOCILIARY BLANKET - protects the respiratory tract; consists of a layer of mucus produced by goblet cells.
INHALED VIRIONS -
LARGER PARTICLES - >10um
SMALLER PARTICLES - <5um
RESPIRATORY SYSTEM - is also protected by innate and adaptive immune mechanism.
Different defenses protecting the gastrointestinal tract:
Acidity of the stomach
Layer of mucus
Antimicrobial activity of digestive enzymes
Bile and pancreatic secretions
Innate and adaptive immune mechanisms
Largest organ of the body; its outer layer of keratin provides a mechanical barrier.
SKIN
Entry via the skin for FURTHER PROTECTION:
Low ph
Presence of fatty acids
Innate and adaptive immunity
Presence of migratorty dendritic cells (Langerhans cells)
Viruses that are both transmitted by and replicate in arthopod vectors.
Arboviruses
Constantyly cleansed by flow of secretion (tears) and mechanical wiping of eyelids.
CONJUCTIVA
From the route of entry restricts viral shedding to respiratory secretions, as in the case of canine parainfluenza virus infection
LOCAL SPREAD
from the route of entry results in shedding from MULTIPLE MUCOSAL SURFACES
VIREMIC SPREAD
Pathological changes in cells:
Vacuolation
Ballooning degenation
Synctium formation
Hypertrophy
Hyperlasia
Nucleolar displacement
Margination of nuclear chromatin
Production of cytoplasmic
Production of intranuclear inclusions
abnormal structure that form in the nucleus or cytoplasm of a host cell during a viral infection.
INCLUSION BODIES
Spherical inclusions in nerve cells that are a sign of rabies infection.
NEGRI BODIES
