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viral, host and environmental factors that determine whether infection…
viral, host and environmental factors that determine whether infection results in disease
disease=tip of iceberg; i.e. most infection X cause disease and will pass unnoticed
host factors
age
sex
nutritional status
species/breed
immune status (vaccination/previous infection)
physiological stress (high productivity animals/pregnancy)
co-infections with one or more pathogens
viral factors (properties)
infectivity (R0--how many onward case does each case cause)
e.g. R0=18, means 1 person infected, spread to 18 other ppl
geographical origin of virus: endemic/exotic (whether animal has encountered the disease before)
transmission route
immunosuppression
tropism for immune cells (e.g. macrophages--canine distemper; lymphocytes--HIV/FIV)
viral factors (viral virulence factors)
virus (even same virus) can differ in pathogenicity
non-coding virulence factors
untranslated region of genome
papillomavirus
diff ability to cause cancer
rotavirus
fluid secretion
influenza virus
diff position of protease cleavage site in haemagglutinin protein in inside influenza virus
determine high and ow pathogenic strains
easily cleaved haemagglutinin protein=primed for infection (highest pathogenicity)
environmental factors
contamination of environment
water supply
climatic conditions
e.g. change distribution of different insects-->impact insect-borne diseases
Quality of nutrition
pasture
feed
stocking density
impacts ease of transmission
impacts dose of virus per animal
management practices (imported animals/new feedstuff needs to be qurantined)
veterinary policy
vaccination programs