Abstract:
This research was initiated to investigate a high
mortality problem occurring in market age broiler
chickens in Oregon. Initial field investigations
revealed that mortality was due to the systemic bacterial
infections. The subsequent laboratory experiments
suggested that suppressed short-term, non-specific innate
immunity rather than pathogenic properties of bacteria
caused the systemic bacterial infection. The objectives
of research described were to analyze and characterize
the type of innate immunity in chickens by developing a
model; analyzing this immunity with artificial induction
by inactive agents; and demonstrating the involvement of
the type of immunity in viral infection.
Escherichia coli strain 01:K1 causes systemic
infection in chickens after the intra-airsac inoculation.
Levels of immunity can be determined by the viable
organism count in the internal organs of infected birds.
Bacterial counts were significantly lower in the liver or
spleen of vaccinated birds at 6, 12 or 24 hrs after
inoculation than in controls. An oil-adjuvanted vaccine
showed some deterioration in its immunogenicity after
prolonged storage or heating at 100 C.
Non-specific innate immunity induced by intravenous
injection of inactivated bacteria or LPS, or subcutaneous
injection of silver nitrate induced significant immunity
in 24 hours against infection with E. coli based on
viable bacterial counts in the spleen. Nonspecific
immunity induced by formalin-inactivated Staphylococcus
aureus cell suspension (FSA) was comparable to specific
immunity induced by a specific vaccine as determined by
cumulative mortality during 7 days and the viable
bacterial count in the spleen after infection. This
nonspecific immunity appeared as early as 6 hours and
lasted for less than 72 hours after stimulation.
Birds vaccinated with NDV vaccines induced significant
protection against challenge exposure with 01:K1 strain
for a period of 2-8 days post vaccination. Secondary
NDV vaccination administered 14 days later failed to
induce immunity against E. coli when infected 1 or 5 days
after the vaccination. Treatment with cold stress or
corticosterone suppressed the induction of nonspecific
immunity by FSA or NDV vaccination.
These results indicate that nonspecific innate immunity
against E. coli in chickens can be induced by injection
of killed bacteria or primary NDV vaccination.
