Virulence of Bordetella bronchiseptica from pigs with or without atrophic rhinitis

The virulence of 17 isolates of Bordetella bronchiseptica from 13 pig herds was compared by intranasal infection of gnotobiotic piglets and LD50 tests on mice. Of 59 piglets given 8.1-10-5 log 10 colony-forming units (cfu) of isolates from two herds with atrophic rhinitis (AR isolates) or isolates from six unaffected herds (non-AR isolates), 16 died of acute pneumonia; the survivors developed non-progressive turbinate hypoplasia and chronic pneumonia. Infection of 11 piglets with c. 3.0 log to cfu of three AR isolates or three non-AR isolates caused turbinate hypoplasia, but only slight pneumonia and no deaths. There were no significant differences between the virulence of AR and non-AR isolates in piglets. In LD50 tests in mice, there were no significant differences between the results from six AR isolates and six non-AR isolates, or from toxin prepared from two AR isolates and one non-AR isolates was fairly uniform, and that other factors must be responsible for the occurrence of progressive lesions of atrophic rhinitis in some but not all infected herds.