| | | | | What problems do conventional vaccines present? | Despite the excellent results obtained with conventional vaccines in the control of most porcine diseases, certain problems exist such as the impossibility in differentiating between vaccinated and sick animals and the difficulty in finding a vaccine which is effective against all diseases.
| | |
Conventional vaccines have been and continue to be the main immunological basis for fighting most porcine diseases. Nevertheless, this type of vaccine presents several problems. Amongst the most important are the following:
MAIN DISADVANTAGES OF CONVENTIONAL VACCINES |
Safety: Reversion to virulence. |
Lack of total inactivation. |
Contamination. |
Secondary effects: Inflammation. |
Fever. |
Hypersensitivity. |
Immunosuppression. |
Cold chain: Refrigeration. |
Not available against all diseases: ASF. |
No differentiation between vaccinated and sick animals. |
|
|
|
The problems, albeit infrequent, found in conventional vaccines are the possible reversion to virulence of live vaccines and failures in the total inactivation of inactivated vaccines. Other problems that can also affect the safety of vaccines come from contamination by non-detected bacterial or viral agents. On some occasions, the cell lines where the vaccine inoculum is prepared can be contaminated with viruses that do not produce a cytopathic effect, and which replicate in parallel with the vaccine virus. Although these problems should be detected by quality and safety controls of the different batches of vaccines, this is not always the case.
SECONDARY EFFECTS:
The secondary effects caused by vaccination with certain conventional vaccines represent further problems. Generally, these secondary effects are only produced at a local level with inflammation or edema occurring at the point of inoculation. Occasionally there is fever, and more rarely, serious problems may occur such as hypersensitivity reactions or passing immunosuppression. |
Photographs of the African swine fever virus (ASF) under electron microscope and lesions caused by it. |
COLD CHAIN. Conventional vaccines, both inactivated and attenuated (in the latter it is critical), need to be kept under refrigeration at temperatures of around + 4 to + 6 º C during storage and transport. On some occasions, particularly in under-developed areas, these requirements cause the vaccines to lose effectiveness as they are not kept under adequate conditions before use.
NOT AVAILABLE AGAINST ALL DISEASES: Vaccines have not been developed against all porcine diseases using these conventional technologies. Therefore, up to now it has not been possible to develop an effective vaccine against the African swine fever virus. This disease generates significant economic and social losses in many African countries, hindering the development of the pig industry. |
The molecular and antigenic structure is identical for both the infectious and vaccine agent as the antibodies induced by both are identical. |
NO DIFFERENTIATION BETWEEN VACCINATED AND SICK ANIMALS. Perhaps the main problem with this type of conventional vaccine is that it is impossible to distinguish between vaccinated animals and sick animals. Given that conventional vaccines consist of the complete viruses or bacteria (attenuated or inactivated), the immune system detects the same antigens that are produced by an infection and its response is therefore the same. This disadvantage has prevented, for example, countries of the European Union from using vaccines against certain diseases such as classical swine fever. Despite being very effective, a vaccinated animal cannot be distinguished from a sick or carrier animal. Some of these problems have been resolved with new technologies and the production of new generation vaccines as we will see in the next chapter.
CSF virus. |
|
|
| |