Fowl cholera is a septicaemic disease of fowls caused by Pasteurella avicida. Several outbreaks have occurred in New South Wales and some very heavy losses have been sustained. As well as causing septicaemia the organism may localise in the wattles, causing oedema of the wattles, and in the upper respiratory tract causing coryza, sinusitis, etc. The etiological agent was known in the days of Pasteur, who claimed to have been able to immunise fowls against it. However, nobody has been able to repeat Pasteurs work and obtain the satisfactory results he claimed, and control of the disease has depended on sanitation.
The causal organism is known to live for only a short period away from the host, in fact subculturing at intervals of a few days is necessary to keep it alive in the laboratory. This has led to the search for "carriers." Pritchett, Beaudette and Hughes (1930) were able to isolate Past. avicida from the nasal cavities of a number of birds in flocks in which fowl cholera was endemic; and removal of such "carriers" considerably reduced the incidence of the disease during the following year. They were able to show also that the nasal cavity was the natural portal of entry of Past. avicida.
It may be taken, then, that the disease is perpetuated by "carriers" and that spread from farm to farm usually takes place by the introduction of such birds. Therefore the primary consideration in control is never to allow birds which have passed through an outbreak to come into contact with normal fowls. The method of detection of "carriers," employed by Pritchett and associates (loc. cit.), whilst highly successful in controlling the disease, obviously is impracticable on a wide scale.
Various workers have investigated the usefulness of a tube agglutination test for diagnosing the disease, but none appears to have been satisfied with his results. In 1939, Shook and Bunyea (1939) reported on the use of a stained antigen whole blood test for the detection of "carriers." 133 reactors were obtained in one flock tested and tube agglutination tests on these were in complete agreement with the rapid tests. The reactors were removed from the flock and in the succeeding year no deaths from Fowl Cholera occurred, although in the preceding two years deaths from this disease had been heavy. No attempt was made to determine whether the positive reactors were actually "carriers."
Recently, an outbreak of Fowl Cholera was encountered here in which the disease was confined to the birds in one large yard. Within a few weeks some 400 birds died, leaving 200 survivors. Application of the whole blood-stained antigen test to these by Mr. D. G. Christie. B.V.Sc., using a similar type of antigen to Shook and Bunyea (loc. cit.) yielded eight positive reactors. One of these had a large necrotic mass, which was discharging in one wattle and Past. avicida was isolated from the discharge. Swabs were taken from the nasal cavities (through the palatine cleft) of the eight reactors and cultured in an attempt to recover Past. avicida, but all attempts resulted in failure. Although we failed to isolate Past. avicida from the nasal cavities of the reacting birds, it is possible that they were "carriers," and it will be seen that the test detected one bird which was proved to be excreting the organism.
Conclusion: It has been shown by American workers that the "carrier" fowl is the means by which Fowl Cholera is perpetuated on a farm and is spread from farm to farm. Circumstantial evidence suggests that such "carriers" may be detected by the application of a stained antigen — whole blood agglutination test, and that elimination of these birds leads to control of the disease. References: Pritchett, I. W., F. R. Beaudette & T. P. Hughes. (1930) — J. exp. Med. 51 : 249.
Shook, W. B. and H. Bunyea (1939) — Poultry Sci. 18 : 146.