IMMUNOLOGY OF LARYNGOTRACHEITIS 



13 



satisfactory immunity, but lead to erroneous conclusions in regard to the efficacy 

 of the method. 



The Vaccination of Roosters and Fowls 



A mixed group of birris was available for this experiment, consisting of 12 

 roosters and 23 fowls. All of these birds had reached maturity and the bursa of 

 Fabricius had completely involuted. The birds were placed in individual cages, 

 and 27 of them inoculated in the bursal fold, while 8 controls were inoculated 

 intratracheally. Eight of the inoculated birds came down with infectious laryn- 

 gotracheitis in five days, which is about the average incubation period for fowls in 

 production, and two of them died. Seventeen days after vaccination the birds 

 were inoculated intratracheally with infectious laryngotracheitis virus, and all 

 were found to be imnuine, except the controls. The controls contracted the dis- 

 ease and three died. 



The surviving birds were held under observation for twenty-five days without 

 any further indications of disease, except that one of the vaccinated fowls de- 

 veloped proctitis and inflammation of the oviduct, in addition to infection of the 

 bursa of Fabricius. This condition led to prolapse of the oviduct. If this bird 

 had been in a flock instead of in an individual cage, she would undoubtedly have 

 been picked to death and the fatality charged to cannibalism without the real 

 facts of the case being known. 



The Vaccination of Pullets and Cockerels 



In this experime^it the pullets and cockerels were divided into four groups, 

 according to age, 200 being vaccinated in the bursa of Fabricius while 82 were 

 held in separate cages as controls. Fourteen days from the date of vaccination 

 all of the birds, including the controls, were inoculated intratracheally with in- 

 fectious laryngotracheitis virus. The results of this experiment are summarized 

 in Table 10. 



Table 10. — Tests of Immunity of Pullets and Cockerels Following 



Bursal Vaccination 



In Group 1, as indicated in Table 10, all of the vaccinated birds were protected, 

 except five which apparently infected themselves soon after inoculation, and had 

 mild attacks of infectious laryngotracheitis. It would appear natural for some 

 of the birds to infect themselves before sufficient immunity was developed for 

 protection, either by picking the vaccinated parts or from contaminated droppings 

 on the floor. Of the 17 controls, 1 was found to be naturally immune, and 16 

 contracted the disease from which 10 recovered and 6 died. The birds were held 

 for forty days after vaccination and none of them showed any after eflfects of the 

 treatment. 



