Part 1:

An article that I read recently asked if there was a new strain of canker, and it reminded me that there are indeed strains of the canker-causing organism. Canker is the name of the disease caused by the tiny parasite called Trichomonas gallinae. It occurred to me then that, as a reply to the question asked by this article, I might present some background information on strains of Trichomonas gallinae, and their importance to all of us.

I have drawn the information in this article from a number of important old and some fairly current scientific papers selected from my files. Incidentally, in the following material, when I refer to the canker organism, I will likely use the terms "Trichomonas gallinae, T. gallinae (the latter is simply a shortened form of the full scientific name), trichomonad, trichomonas and canker organisms" interchangeably -- all mean the same thing.

Infection by this organism was first identified in Europe in 1878 by a researcher named Rivolta. Many years later in the USA, a scientist named Robert Stabler, conducting research in the state of Colorado, pioneered extensive work on the organism in pigeons -- in fact in 1938, he gave the organism its scientific name, Trichomonas gallinae.

In a 1948 publication on the subject, he noted that not all pigeons that harbour the organism die of the infection, or even have internal changes to indicate the presence of this organism. As well, he found that youngsters from some parents in a loft nearly always died of canker in a few days or weeks after hatching, whereas certain other parents, although infected, raised healthy youngsters indefinitely.

Obviously these facts gave rise to the idea that there were strains with differing abilities to cause disease, a suggestion that had also been proposed by other scientists who had worked on canker in pigeons.

To test this idea, Dr Stabler then set up an experiment in which he used canker organisms that he arbitrarily designated as "strains" (see explanation in the next paragraph), from five different sources: Strain 1 from an infected wild youngster, Strain 2 from a healthy adult King, Strain 3 from a healthy adult Carneaux, Strain 4 from an adult racing pigeon that had a history of transmitting lethal canker to his youngsters and to at least three successive hens, and Strain 5 from the mouth of a peregrine falcon that had died with severe canker of the mouth.

(Note that canker caused by T. gallinae occurs in birds of prey in which it is called "frounce". Broadly related organisms in this group also cause infections, variously, in the reproductive systems of humans, cattle, and sheep, and in the digestive tracts of domestic chickens and turkeys. I have also seen it in devastating outbreak form in small aviary finches in which the disease very much resembled that seen in the oral cavity of young pigeons.)

Dr Stabler defined "strain" as the particular canker organisms removed from the mouth of an individual bird, even though he recognized the possibility that any given bird might harbour more than one strain. The results he obtained seemed to justify the use of the organisms from a particular bird as "a strain", at least in terms of their ability to cause disease. He maintained the five individual strains mentioned previously by inoculating them by eyedropper into the mouths of clean pigeons, and took great care to be sure that the different strains weren't accidentally mixed. The clean pigeons he infected with these five strains came from his own loft of racing pigeons that he knew were free of canker-causing organisms.

In the first experiment, he used 25 of his own young birds, aged 6 weeks, 5 1/2 weeks, 5 1/2 months, 7 months, and 9 months, with five birds in each group. One bird in each age group was inoculated by mouth with Strain 1, one in each group received Strain 2, and so on. Results showed that the Strains 1, 4, and 5 caused severe signs of disease that ended in the death of all except two youngsters, a 7 and a 9-month-old bird infected with the Strain 4. These two birds had severe canker for over a week, but they recovered. Strains 2 and 3 either didn't produce signs of disease in the youngsters they infected, or the infection was very slight and lasted only 2-4 days.

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Gordon A Chalmers, DVM,

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