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In follow-up work, Dr Stabler showed that Strain 1 (which became known in trichomonad circles as his famous "Jones' Barn" strain) obtained from the wild youngster with canker, was the most deadly of the five strains, killing 12 of 13 birds inoculated with it in an average of 10.6 days. Over all, he was able to show that, of 119 pigeons infected successively with this potent strain, 114 (95.8%) died in 4 to 18 days. In later work, he showed that Strain 1 was deadly even if only one organism was placed in the mouths of susceptible pigeons. Obviously, this single organism multiplied rapidly into the thousands or more to cause serious illness.

These results showed that there was a marked difference in the ability of these five different strains of T. gallinae to cause disease in pigeons. These strains varied from those that caused little or no disease to those that caused high losses. Obviously, there were also strains that were intermediate in their ability to cause canker, since they were able to cause serious illness from which most birds eventually recovered.

In important later studies, Dr Stabler was able to show that mild strains of the canker organism were able to protect birds against more deadly strains, a finding that continues to have practical application today. To confirm these results, he first gave eight of his own trichomonas-free youngsters the relatively potent Strain 5 obtained from the peregrine falcon. All developed severe canker of the mouth, six birds recovered and two died.

Fifty-four days after the initial infection with Strain 5, the six survivors were given the very deadly Strain 1. None of them developed evidence of disease during the following month. These six birds were then killed and examined at post mortem. There was evidence of scarring of the liver of three birds, findings that suggested infection from the previous dose of organisms. The other three birds were almost completely free of signs of infection. The only significant finding in these birds was the loss of the palatal fringe on the roof of the mouth. (Dr Stabler believed that, in every case examined, this change was highly characteristic of evidence that the canker organism was the cause.)

He then repeated this experiment with eight more clean youngsters that were first given the mild Strain 3 from the adult Carneaux. Only two youngsters developed a mild form of the disease. About a month later, all eight birds were given the deadly Strain 1. In the next three weeks, only two of the eight birds developed signs of canker. One had a mild form of the disease, and the other had a severe form from which it eventually recovered.

Post mortem examinations of these eight birds determined that tissues of seven birds were completely normal, and that the bird that developed severe canker had severe changes of canker in the liver. At the same time, as a control, Dr Stabler inoculated 13 youngsters from his own loft of trichomonas-free birds with deadly Strain 1; 12 of the 13 birds died. Thus, these experiments demonstrated that infection by a mild strain of T. gallinae conferred protection against a more deadly strain of the organism. However, the duration of that immunity wasn't determined at that time.

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Gordon A Chalmers, DVM,

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