Investigation into the pathogenesis of atrophic rhinitis in pigs. II. AR induction and protection after intramuscular injections cell-free filtrates and emulsions containing AR toxin of Pasteurella multocida.

The intramuscular administration of the cell-free culture filtrates of two AR pathogenic Pasteurella multocida (PM) isolates caused Atrophic Rhinitis (AR) in piglets. The culture filtrate of a non-AR-pathogenic PM isolate did not cause AR lesions after intramuscular injection. The severity of the AR lesions appeared to be correlated with the quantity of injected toxin. As the quantity of administered toxin increased, the piglets showed clinical growth retardation, icterus and mortality. Besides lesions typical of AR, severe liver degeneration was observed at necropsy; this liver degeneration was sometimes accompanied by fibrosis. After emulgation of the cell-free culture filtrates in incomplete Freunds adjuvant, AR was caused by administration of the toxin-containing emulsions in piglets of 3 and 6 weeks of age. An experimental water-in-oil emulsion containing the AR toxin of Pasteurella multocida caused AR when intramuscularly injected in 1- to 4-week-old piglets. A PM-AR toxin challenge method is described. After injection of the toxin into piglets born from sows vaccinated against AR, protection was demonstrated. Ten of the 12 piglets (83%) challenged at the age of 3 weeks showed protection. Six animals of the 12 pigs (50%) injected with the toxin at the age of 6 weeks, showed no protection. Differences in protection were noted between and within the litters. After injection with the toxin, all piglets of 3 and 6 weeks of age born from non-vaccinated sows showed deviations typical of AR.