Bacillary white diarrhoea of poultry and its eradication in the Union of South Africa

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(1) Standardization should be carried out with all strains of organisms and antigens prior to utilization for testing purposes. Single strains of organisms should be submitted to low dilution testing before use as antigens. (2) Known negative fowl serum should be used for negative control tests. (3) The water of condensation should be poured or siphoned out of flasks of growing cultures before washing off the growths for the preparation of antigen. (4) S. pullorum antigen appears to be a much more stable product than S. gallinarum antigen. Reliable results can be expected from S. pullorum antigens for at least two years after preparation, but S. gallinarum antigens over a year old should be checked prior to use for testing purposes. (5) The highest titred antigens are obtained by using single strains of S. pullorum or S. gallinarum for antigen production. (6) In most cases more positive reactors are picked out in badly infected flocks when single strain antigens are used, in preference to antigens made up of a number of strains. (7) The higher the titre of the single strain antigen the more positive reactors that are picked out, but one must be careful of so-called supersensitive strains. In a small number of cases a lower titred antigen may pick out more reactors than an antigen with a high titre. (8) To expedite the eradication of positive reactors from an infected flock it is advisable to use single strain antigens with high values. (9) The addition of small amounts of phenol has some effect in influencing the phenomena of "cloudy reactions" and flocculation in the tube test. The amount of normal NaOH solution added to antigens to prevent these two phenomena should be regulated by the pH of the antigen. Both S. pullorum and S. gallinarum antigens are made slightly more sensitive when adjusted to a pH of 8.2 to 8.5 by the addition of normal NaOH solution. The addition of the normal NaOH solution to the antigen should take place just prior to its use for testing and, bearing in mind that the density of the antigens is affected by this addition, due allowance should be made for this effect. (10) In South Africa complete agglutination in a dilution of 1:10 of a serum and antigen is regarded as indicative of a positive bacillary white diarrhoea or fowl typhoid carrier. (11) Titrations of sera of different fowls show how marked the variations are in the end points of agglutination. Marked fluctuations are shown in the positive titre of individual fowls tested over a period of time. (12) The intermittent reactor should not be regarded entirely as a fowl that produces agglutinins intermittently. Other factors such as the use of antigens of a low standard titre, and the dilution that is considered to indicate a positive reactor, must be borne in mind. (13) It does not always follow that an antigen having a high standard titre will always give a higher positive titre with any one known positive fowl serum, than an antigen of a lower standard titre. (14) There is little, if any, difference in test results when using either a S. pullorum or a S. gallinarum antigen provided the S. gallinarum antigen is only a few weeks old. Both S. pullorum or S. gallinarum antigens will pick out either bacillary white diarrhoea or fowl typhoid carriers; therefore there does not appear to be anything gained by using an antigen made up of a mixture of strains of S. pullorum and S. gallinarum (15) Differences in the positive titre, in some cases marked, will be observed when the same sample of serum is submitted to a group of S. pullorum or S. gallinarum antigens. (16) All carriers of either bacillary white diarrhoea or fowl typhoid will not be picked out by every antigen used, and therefore all positives are unlikely to be detected by one round of testing. (17) False positive reactions may be caused by the use of dirty glassware, but the more common cause is the presence of organisms, not belonging to the Salmonella group, isolated from the ovaries or from the heart blood. Most of these false positive reactions are found in the low test dilutions. Not all the organisms that set up these false positive reactions give rise to acid with lactose, and some ferment saccharose. These organisms give rise to no symptoms in the carriers, which appear to be healthy birds. (18) Young stock should be tested only after egg-laying has commenced, or at five or six months of age. Young birds from badly infected farms frequently give doubtful positive reactions to the agglutination test.