6 



Appearance of Infection in Flocks Previously Negative 



Table 3 gives the testing results for flocks which had been non-reacting for 

 one or more years but showed infection in 1941-42. One flock (Number 2) was 

 partially retested with no reactors the previous season. It is quite possible that 

 the infection was not completely eradicated from this flock. Only one reactor 

 was detected among the 3,524 birds tested. 



Table 3. Appearance of Infection in Flocks Previously Negative 



1941-42 Season 



Number Positive 



Flock of Years Flock Number Tests Explanation for Infection 



Negative Total Tested Percent 



indicates retests. 



Among the other five flocks, only one revealed more than one percent reactors. 

 This flock had been negative for 14 consecutive years. The infection might be 

 attributed to contact with stock from a neighboring flock whose pullorum status 

 was unknown. 



Flocks 1, 3, and 4 had been negative for 8 or more consecutive years. Flock 

 1 had 24 reactors among 4,094 birds. The source of infection could not be de- 

 termined definitely, although it was ascertained that there was some laxity in 

 carrying out certain preventive measures. 



The infection detected in Flock 3 was in a group of birds returned from an 

 egg-laying contest. 



The origin of the infection in Flocks 4 and 6 could not be explained in any way. 

 However, in Flock 6 infection existed on the premises two years prior to the last 

 test. 



The number of so-called "breaks" for the 1941-42 season has remained at the 

 same level as in previous seasons. In all cases the amount of infection is very 

 small. With the exception of one case (Flock 3), the source of infection is doubt- 

 ful and at what age the flock became infected is not known. The low degree of 

 infection would suggest that the stock was not highly susceptible to certain strains 

 of 5. pullorum. This does not coincide with observations on New England stock 

 imported into areas where infection is more prevalent. No explosive outbreaks 

 nor heavy infections have been observed in flocks which have been negative for 

 many years. It is reasonable to assume that heavy infections might occur, but 

 it would seem logical that other factors such as strain differences of S. pullorum 



