Purpose of vaccination
To protect the flock from harmful infectious agents
To hyper immunize hens in order to maximize maternally derived antibody passed through the egg to the progeny.
Vaccines may be prepared from live microorganisms or from inactivated (killed) microorganisms; from genetically organized subunits of the pathogenic part of the organism or heat or chemically treated microorganisms that have lost their virulence although keep their antigenicity. Thus, the two main types of vaccines are live vaccine and inactivated vaccine.
Live vaccine
Live vaccines are vaccines prepared from bacteria or viruses whose virulence is reduced by chemical, heat or passage via an animal except for the normal host species. For example, cattle plague vaccine may be prepared from the virus passaged through chick embryos. Occasionally, the live viruses used are related but non-pathogenic strains, beneficial because they will trigger antibody production but will not produce the disease.
Characteristics of live vaccine
Smaller amount of antigen is needed.
Vaccination response relies on multiplication within the bird
Adjuvanting live vaccine is not common
It can be administered in mass via spray or drinking water.
In immuned birds, booster vaccination is ineffective.
It is susceptible to existing antibody present in the bird.
Tissue reaction is visible
There is danger of vaccine contamination
There is rapid onset of immunity
Immunity obtained from live vaccine is short lived.
There is relatively limited combination due to interference of multiple microbes given at the same time.
Inactivated vaccine
Inactivated vaccines are prepared from killed microorganisms that retain sufficient antigenic activity to promote immunity. They are not as potent as live vaccines and different doses at specified intervals are usually necessary to produce effective immunity. Inactivated vaccines often contain adjuvant, usually an aluminium salt such as aluminium hydroxide which enhances the immune reaction. Some are water-based while others are formulated in an oily medium.
Characteristics of inactivated vaccine
Large amount of antigen is needed.
Vaccination response does not rely on multiplication within the bird.
It is always injected in birds.
Adjuvanting killed vaccine is frequently necessary.
There is little danger of vaccine contamination
In immuned birds, additional immune response is frequently seen.
It is more capable of eliciting an immune response in the face of existing antibody.
Combinations are less likely to occur.
There is slower onset of immunity
Immunity for killed vaccine last longer.
There is no tissue reaction outside adjuvant dependent.
Routes of vaccination in poultry
Intramuscular, example, kumarov
Subcutaneous, example, fowl typhoid vaccine.
Intraocular/intranasal, example, Hitchner B1
Inovo, example, marek’s vaccine
Spray, example, lasota.
Drinking water: add skimmed milk in water before reconstituting the vaccine.
Wing stab, example, fowl pox vaccine
Vaccination failure
A vaccination failure is said to occur when after administration of vaccine, the chickens do not develop adequate antibody titre levels and are susceptible to a field disease outbreak.
Factors responsible for vaccine failures in commercial poultry
Stress: Vaccination is stress. A bird being injected with a live vaccine is really being infected with a mild form of the disease. Other forms of stress include environmental extremes (relative humidity and temperature), inadequate nutrition, parasitism and other diseases. These may reduce the chicken’s ability to mount an immune response.Administration and handling of the vaccine: There is vaccine damage by improper handling prior to administration. Live vaccines can be inactivated when exposed to adverse conditions. Store and handle vaccine as recommended by the manufacturer. Live vaccine administered in drinking water can be damaged before they can protect the bird if water sanitizers have not been removed prior to addition of the vaccine.
Maternal antibodies: The immune status of the breeder flock can have an effect on the favorable outcome of offspring vaccination. If the breeder flock has high levels of moving antibodies which pass to the progeny via the egg, they may disrupt the replication of live vaccine viruses as they would for field challenge viruses. This will reduce the immune response to the vaccine.
Immunosuppression: This refers to circumstances where the non-cellular and cellular constituents of the immune system are not functioning properly. The status of the flock immune system must be noted when vaccinating. Chickens may be immunocompromised due to infection with mareks’s disease viruses, chicken infectious anaemia and infectious bursa disease(IBD). Ingestion of feed with high levels of mycotoxins may result in a development of limited protection from vaccination.
Management practices: Poor management applications in poultry flocks may cause vaccine failures such as irregular, poor sanitary practices and irregular vaccination programs.
Vaccine quality: Purchase from well respected pharmaceutical companies whose products are produced under firm quality control measures. Use of vaccines that have been unduly attenuated can result in vaccination failure.
Vaccine strain and specificity: Many diseases are caused by agents that are made up of various strains. For example, there are more than 100 recognized strains of infectious bronchitis virus and over 2000 strains of salmonella bacteria. In few instances, the vaccine may not contain the proper strains of organism required to stimulate protective immunity harmful to the agent causing the field challenge. In spite of the fact that the vaccine is properly administered and sufficient antibody titre levels are present, the chickens still come down with the disease. In recent years, problems with variants are seen with pox, infectious bronchitis virus, marek’s, infectious bursa disease etc.