8 MASS. EXPERIMENT STATION BULLETIN 407 



43. What is a reactor? A reactor is a bird whose serum gives a doubtful or 

 positive reaction in the serum-test fluid dilution of 1-25 after 24 hours' incuba- 

 tion at body temperature. If only doubtful birds are found, they are subjected 

 to further examination. Postmortem examinations are often helpful in making a 

 diagnosis. 



44. Do infected birds always show a positive agglutination test? Occasionally 

 infected birds are discovered at necropsy that did not react positively to the 

 agglutination test. The serum dilution (proportion of serum to test fluid) is an 

 important factor in detecting such birds. The lower the dilution the more infected 

 birds will react. Infrequently, birds may react at one test and not at the next. 

 Such birds are called intermittent reactors. 



45. Are nonreacting infected birds considered as spreaders? The causative 

 organism has been found in eggs laid by such birds. The organism has also been 

 isolated from the ovary and other organs on necropsy. Fortunately such birds 

 are rare, as shown in flocks which are tested annually. 



46. Are all reactors infected with the organism? No. The pullorum test 

 may detect reactors which are infected with other organisms and not with the 

 organism that causes pullorum disease. Birds affected with fowl typhoid react 

 just as strongly with pullorum test fluid as do birds affected with pullorum disease. 

 Infections with the paratyphoid organisms and the common colon bacillus in 

 bircfs may at times cause reactions with the pullorum test fluid. Reacting birds 

 also are observed in which no gross signs of disease can be found. Few such birds 

 are found infected on bacteriological examination. A plausible explanation for 

 failure to isolate the organism from some reacting birds is that such birds have 

 been infected recently or that the organism has been eliminated recently. How- 

 ever, it must also be recognized that the methods of examination have their 

 limitations. 



47. Do all reactors lay infective eggs? No. If the infection is localized in 

 those parts of the body which have no direct relation or communication with the 

 oviduct, the organism is not eliminated through the egg. Furthermore, not all 

 eggs laid by birds with infected ovaries contain the organism. 



48. Should fresh eggs from infected or untested flocks be fed to noninfected 

 stock? No. Investigations have shown that birds may be infected when fresh 

 eggs laid by infected birds are fed. 



49. Why do negatively reacting birds suddenly become positive reactors? 



Nonreacting birds that suddenly react positively, in all probability have been 

 infected recently. Tests have shown that birds may react first between the 

 fourth and seventh day after the first exposure to artificial infection. The avenue 

 of infection, the size of dose, the ability of the organism to infect the bird, the 

 resistance of the bird, and the ability of the bird to produce antibodies are fac- 

 tors which determine the reaction of the bird. 



50. Should the flock be tested annually? Yes. Poultrymen who use part or 

 all of their flocks for breeding purposes should test all birds on the premises each 

 year. The test is a means of detecting infected birds. It does not assure the 

 owner thft once his flock is free from infection it will remain so. Table 1 shows 

 that commercial flocks are vulnerable to infection even though they may have 

 been negative for many years. In New England the amount of infection is small 



