Pasteurella multocida infection in embryonated chicken eggs was studie
d by chorio-allantoic membrane inoculation. Strain differences were de
monstrated in terms of lesion severity and time to death, especially d
uring the first 24 h post-inoculation. A strain of low virulence gave
a clear dose response but more virulent strains did not. Comparable re
sults were obtained by infecting 6-week-old chickens. The main lesions
in inoculated embryos appeared as severe vascular involvement of the
entire embryo and feather tracts, thickening of the chorio-allantoic m
embrane, and enlargement and congestion of the yolk sac. The bacteria
were demonstrated by transmission electron microscopy, either extracel
lularly or multiplying intracellularly in hepatocytes, heart tissue, a
nd in the hyperplastic layer of the chorio-allantoic membrane, with re
sulting damage to the cellular organelles, and severe tissue changes.
(C) 1998 W.B. Saunders Company Limited.