1. The Field of the Invention
The present invention relates to novel bacterial extract vaccines for use in veterinary medicine and to novel methods for preparing such vaccines. The present invention further relates to methods for using the vaccines to immunize animals against a variety of bacterially induced diseases.
2. The Prior Art
Traditionally, bacterial vaccines used in veterinary medicine have been prepared using intact, whole bacterial cells. Necessarily, the bacteria in such bacterial vaccine preparations are severely weakened or killed by such methods as the application of mild heat, cold storage in the presence of thimerosal or formalin, or combinations of these methods. Such alteration of the bacteria is needed in order to reduce, to the greatest extent possible, the risk that the bacteria in the vaccine will produce the corresponding disease once the vaccine has been administered to the animal.
Unfortunately, vaccines prepared from whole bacterial cells are often toxic and produce harmful side effects. This is believed to be due, at least in part, to bacterial endotoxins present in the whole bacterial cells. Thus, although administration of such prior art bacterial vaccines may help to immunize an animal against particular diseases, administration of the prior art vaccines may well result in toxicity and other harmful side effects to the animals vaccinated.
Another disadvantage of many whole bacterial cell vaccines used in the prior art is that such vaccines have frequently been found to produce insufficient immunity in the animals vaccinated. For example, it has been found that whole cell vaccines often do not induce the production of sufficient levels of antibodies to provide adequate long term immunity. This has resulted in less efficient vaccinations and the need to vaccinate the animal populations more frequently.
The development of new animal vaccines against bacterially induced diseases has slowed down significantly in recent years so that the state of the art is only slightly more advanced than it was about 30 years ago. One of the primary reasons for this decline is the ready availability and widespread use of antibiotics in recent years. With the advent of antibiotics, the stimulus for extensive research into antibacterial immunity in veterinary medicine was greatly reduced. However, the situation is now rapidly changing as animals develop resistance to known antibiotics and as the presence of antibiotic residues in food products becomes of increasing concern from the standpoint of public health.
On the other hand, the development of new vaccines in human medicine has moved forward at a much faster pace. Although considerable improvement could still be made with respect to human vaccines, biotechnology and genetic engineering have recently given scientists the capability to refine human vaccines to a very precise level. For example, it is now possible to isolate and purify from a bacterial cell a single desired antigen. Further, once such a specific antigen has been isolated, it is possible to actually map the coding genes and subsequently synthesize that particular antigen in vitro. In this way, essentially unlimited quantities of antigen can be produced for use in human vaccines.
When it comes to vaccines, however, there are important differences between the practice of human medicine and veterinary medicine. For example, human medicine does not envision people's lives in terms of dollars and cents. Thus, the sophisticated antigen synthesis techniques developed for human vaccines are commonly used without regard to cost. With respect to veterinary medicine, however, economic prospects dictate to a large measure the type and extent of vaccination practices which are exercised by animal producers, such as, for example, livestock owners. The result of hard, cold economic reality is that producers cannot afford to use vaccines which are not cost effective. This is particularly true with respect to the production of "minor species" of animals such as sheep and goats.
Therefore, animal vaccine production methods must necessarily be economically realistic if the vaccines are to enjoy widespread usage. Also, the resultant animal vaccines must be effective enough to warrant their use as well as be affordable. Hence, the current sophisticated techniques used for preparing human vaccines are typically cost prohibitive when applied to the preparation of animal vaccines, and other less sophisticated and less expensive methods have been needed in veterinary medicine for preparing economically practical and effective animal vaccines.
In view of the foregoing, it would be a significant advancement in the art of veterinary medicine to provide animal bacterial vaccines which are relatively nontoxic and which substantially avoid the undesirable and harmful side effects of prior art bacterial vaccines. It would be a further significant advancement in the art to provide animal bacterial vaccines which elicit a much stronger immune response in the animals vaccinated than has been characteristic of prior art vaccines. It would be yet another significant advancement in the art to provide relatively simple and inexpensive methods for preparing such bacterial vaccines so as to provide animal vaccines which are both efficacious and affordable. Such bacterial vaccines, such methods for preparing bacterial vaccines, and methods for administering such bacterial vaccines to animals are disclosed and claimed herein.