Serological Methods: possible future developments.

It is evident that there has been a great deal of progress in the development of highly sensitive assays for the presence of specific antibody in poultry sera. It is possible to envisage future developments along a number of quite distinct paths :

1. Extension of the range of tests available using the currently available methods to cover other diseases, or new antigenic variants of recognized pathogens, and even to newly recognized disease-producing agents.

2. Modification of existing test methodology with a view to improving precision, sensitivity, specificity, or reducing costs (hence allowing more samples to be tested).

3. Development of new assay methods with the same objectives cited in 2 above. It is difficult to envisage the exact direction of such developments. There have been extra-ordinary developments in micro-electronics, sensor technology and bio-technology in recent years. It may well be possible to integrate advances in these diverse areas to allow the manufacture of "sensors" mimicking the antigenic structure of pathogens capable of detecting minute amounts of antibody. Ideally such a sensor should be capable of generating a result electronically after appropriate amplification.

4. Finally we should keep in mind that serology is often used as an indirect means of detecting exposure of the birds to an antigen. Use of existing methods and improvements to them which would allow the direct detection of the antigen in infected birds might well be possible. A disadvantage of the currently-used virological techniques is that they can generally only indicate that a group of birds was positive for the pathogen (or it was not present at a detectable level). These techniques usually provide no information on prevalence of infection, the intensity of infection (this might be relevant if more than 1 pathogen is involved), and the tissues affected (a more detailed knowledge of this might improve understanding of disease epidemiology and pathogenesis). Serological techniques such as immunofluorescence and Elisa have been used for the detection of antigen in clinical specimens directly or after passage in a culture system. The much more widespread availability of genetic engineering techniques such as Polymerase Chain Reaction (PCR) is also likely to facilitate the identification of small numbers of pathogens in clinical specimens. Future improvements in these methods may allow decreased dependence on using serology to detect exposure to disease. They might also be of use in monitoring "take" of a vaccine by taking samples at an appropriate time after vaccination.

It is difficult to predict the speed at which developments will occur among each of the above strands.