1016 
ANIMAL DISEASES 
Figure 1 
0 1234 S6789 10 1112 
Aee tn months 
Figure 1. — Predicted Incidence of Recovery of Borde- 
tella bronchiseptica from the Nasal Cavity of a Group 
of Naturally Infected Pigs. 
After the peak incidence of infection is 
reached there is a gradual i-ecovery from infec- 
tion. This is well illustrated in the previous two 
figures. Unfortunately, recovery in a popula- 
tion is not complete. 
An expected 10 to 15 percent of the breeding 
animals remain infected to initiate the infection 
in their offspring thus starting the cycle over.^^ 
It is also apparent from the fact that the disease 
reoccurs in farrowing after farrowing, that 
resistance to infection is not transferred from 
recovered dams to their offspring via colostrum. 
Recovered swine are extremely resistant to 
reinfection. Almost all of the virulent challenge 
inoculum will have disappeared from the nasal 
cavity within 1 hour post-challenge, while viable 
organisms are readily recoverable from the 
nasal cavities of susceptible control animals.® 
This resistance will last at least for several 
months.*^ It is not associated with the presence 
of demonstrable bactericidal substance,*^ nor 
is it associated with significant levels of cir- 
culating, agglutinating antibody." 
Not all isolates of B. bronchiseptica are of 
equal virulence for swine. One canine origin 
isolate has been demonstrated to be regularly 
eliminated from the swine nasal cavity by the 
sixth to seventh week post-inoculation. In an 
effort to determine the reason for this removal, 
several aspects of the host-basterium interac- 
tion were examined. It was found that the early 
tissue damage produced by the low virulence 
strain was fully equal to that produced by a so- 
called virulent strain.^ The major difference was 
that numbers of organisms began to decline be- 
fore significant gross pathology was produced. 
In an attempt to explain the more rapid disap- 
pearance of the low virulence organism from 
the nasal epithelium, a comparison of phagocy- 
tosis of the low virulence and a fully virulent 
isolate by swine leukocytes was made. The low 
virulence strain was ingested by leukocytes in 
much greater numbers than the so-called vir- 
ulent isolate.® It is speculated that the so-called 
low virulence isolate failed to produce gross 
lesions simply because it was more rapidly re- 
moved from the nasal cavity by phagocytosis. 
A comparable situation is believed to occur 
in pigs that are immunized with a suitable bac- 
terin preparation of B. bronchiseptica. In this 
case the nasal infection is usually cleared in 6 
to 8 weeks. Such bacterin preparations will 
stimulate significant levels of circulating, ag- 
glutinating antibodies' even though the nat- 
urally occurring infection usually does not pro- 
duce similar titers until about the 4th to 5th 
month postinfection. 12 n seems likely that by 
4 to 5 months postinfection enough nasal dam- 
age has occurred to allow invasion of B. bron- 
chiseptica into the deeper tissues which results 
in stimulation of antibodies. 
Figure 2 
12 16 20 24 28 32 36 40 44 
weeks weeks weeks weeks weeks weeks weeks weeks tveeks 
Age in weeks 
Figure 2. — Recovery Rate of Bordetella bronchiseptica 
from the Nasal Cavity of a Group of 30 Naturally 
Infected Pigs. 
