Standardization of reagents for serological tests to detect infections in poultry

Summary

The use of standardized reagents is necessary for correct interpretation of diagnostic tests and vaccination responses and for ensuring the purity and potency of vaccines. Antigens used in serological tests must be prepared in a manner such as to minimize the chance of non-specific reactions. This applies in particular to reactions to those contaminating agents and substances likely to be encountered under field conditions. In order to make pure antigens, it is necessary to use seed and substrate known to be free of extraneous agents and to avoid if possible the use of any materials which are likely to produce cross-reactions. Similar care must be taken with the preparation of positive and negative control sera. It is also important that reagents do not contain virulent agents which may be a hazard in the field situation. The sensitivity of the test system must be carefully adjusted and the procedures should be carried out in a consistent manner so that results are not influenced by factors such as reagent concentration and incubation conditions. The availability and use of international and national standard reagents is discussed. Their use is of great value in reducing assay variation between results obtained at different times or by different workers. They also enable meaningful antibody levels to be set for such purposes as diagnosis or vaccine potency tests.

A great variety of serological tests is available: their suitability depends upon the particular application for which they are required. Some are simple and rapid and suitable for mass screening but they may be lacking in sensitivity. Care must also be taken in some types of test to ensure that the reagents have a suitable antigenic spectrum. Results of serological tests should be interpreted in the light of other knowledge about the environment of the birds which may affect their responses.