Fowl cholera: cross-protection induced by Pasteurella multocida separated from infected turkey blood.

Crude liver homogenates from turkeys that died of fowl cholera produced by serotype 1 or 3 Pasteurella multocida induced cross-protection. Pasteurella multocida harvested from the blood of infected turkeys by a centrifugal technique were as immunogenic as the liver homogenates. Neither bacterial cell-free blood plasma nor washed P. multocida from infected turkeys induced significant cross-protection. Blood plasma containing P. multocida induced significant cross-protection. Pasteurella multocida grown in the turkey underwent bacteriolysis after thawing from a frozen state. Filtered lysates did not induce cross-protection when used as vaccines whereas unfiltered lysates did. Membrane filters impeded passage of immunogenic material.