Introduction Course to Porcine Immunology

WHAT ARE THE PROBLEMS OF CONVENTIONAL VACCINES? 


Although conventional vaccines have been very successful in the control of most porcine diseases, they present some problems, such as the impossibility to differentiate between vaccinated and infected animals and the difficulty of obtaining an effective vaccine against every disease. 


Conventional vaccines have been (and still are) the immunological basis in the fight against most porcine diseases. However, several problems arise when using this type of vaccines.

Some of these problems are:
 

SAFETY.

The possible reversion to the virulent form of live vaccines and failures in the inactivation of inactivated vaccines are the problems (although they are not frequent) that can be found when using conventional vaccines. Another problem is in regard to their safety. There is a danger of contamination by non- detected virus or bacteria. Sometimes the cellular lines used for the preparation of the vaccine may be contaminated  by virus that do not produce any cytopathic effect, yet that replicate at the same time as the vaccine virus does. Although safety and quality controls should detect these contaminations, they sometimes fail to do so.   

Vaccine: efective and durable response.

MAIN PROBLEMS OF CONVENTIONAL VACCINES
Safety: Reversion to virulence.
Incomplete inactivation.
Contaminations.
Secondary effects: inflammation. 
Fever.
Hypersensitivity
Immunosuppression.
Cold chain: refrigeration.
Not available against all diseases: ASF
Non-differentiation between vaccinated and  sick animals.

 

SECONDARY  EFFECTS.

The secondary effects of some conventional vaccines are one of the problems observed. Usually, these secondary effects are only produced at a local level, with inflammation or oedema at the inoculation point. Sometimes fever is also present, and more rarely more serious problems can occur, such as hypersensitivity or transitory immunosuppression.

COLD CHAIN 

Conventional vaccines, both inactivated and attenuated (specially in the last ones) need to be kept refrigerated  (+4 to +6ºC) during their storage and shipment. On certain occasions, this requirement makes difficult to maintain the effectiveness of the vaccines, especially in under-developed areas.

PPA Virus

Lesions of PPA virus

NOT AVAILABLE AGAINST ALL DISEASES. 

It has not been possible, using conventional techniques, to develop vaccines against all the porcine diseases. There is no effective vaccine against African Swine Fever virus, for example. This disease produces huge economic and social loses in many African countries, and impairs the development of the porcine industry.  

Pictures of African Swine Fever virus using electronic microscopy. Spleen lesions induced by ASF virus.


IMPOSSIBILITY OF DISCRIMINATING BETWEEN SICK AND VACCINATED ANIMALS.    

This may be the most important problem related to conventional vaccines. Due to the fact that conventional vaccines are made of complete virus or bacteria (inactivated or attenuated) the immune system detects the same antigens as it would in a natural infection, so the response is the same. This problem has caused countries of  the European Union, for example, to not use vaccines against some diseases such as Classical Swine Fever; although these vaccines are highly effective, they do not allow the differentiation between vaccinated animals and sick or carrier animals. 

not distinguishing antibodies

Molecular antigenic structure is identical in the infectious agent and the vaccine agent. Induced  antibodies are also identical.  

CSF virus.

CSF virus 

Some of these problems have been solved by the new technologies and the production of new generation vaccines, as we shall see in the following chapter. 

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