The other side of Immunisation
In the last few decades, the poultry industry has grown rapidly all over the world. This advancement of the poultry industry has bot been without the occurrence of several new and re-emerging diseases, like newcastle and Marek’s diseases. To counter the disease threat, immunisation with both live and killed vaccines has been widely adopted. However, the immune response has sometimes been linked to adverse reactions or indirect effects. A balance has to be made between establishing the required protection and creating an adverse post-vaccination reaction.
This article is an attempt to discuss the post-vaccination reaction (PVR) and to share our experience of handling it.
Reactions inherent to inoculation
These may be local or general reactions. Local reactions include pain, swelling, redness, tenderness or the development of a small nodule or sterile abscess at the site of injection. General reactions include fever, decreased performance and other constitutional symptomps. Most killed bacterial vaccines cause some general reactions and localised tissue damage at the site of injection due to reaction with the adjuvant.
One major factor is the production of respiratory diseases in poultry which results from our attempts to control it via vaccianation. Improper vaccination contributes to respiratory disease in three ways:
- By causing too strong a vaccination reaction
- By causing a ‘rolling reaction’ as the result of incorrect administration or timing of vaccination. These reactions start slowly and do not stop. Generally, the cause can be traced to not all the birds being injected. Those that are injected begin to react, producing more vaccines virus that infects the unprotected birds.
- By failing to induce immunity to field challenge. Live vaccines against Newcastle disease and infectious bronchitis produce immunity only after a respiratory reaction occurs. Without some respiratory reaction, there is no immunity. Vaccination therefore becomes a balancing act between obtaining too much respiratory reaction contributing directly to the production, creating inadequate immunity to resist field challenge.
The severity of respiratory reactions after vaccination depends on:
- Level of maternal antibody – more antibodies lead to more reaction
- Vaccine strain – more virulent strains produce stronger reactions.
- Age – generally, younger birds react more strongly
- Vaccine dose – higher doses give more reaction
- Route of administration – administration in water gives less reaction than aerosol
- Lentogenic vaccines of Newcastle disease are inevitable, ranging in severity from slightly wet tracheas to production of the plug at the bifurcation of the trachea.
- Concurrent E. coli & Mycoplasma gallisepticum infections.
- Low humidity
- Vaccination via eye drop or drinking water lead to minimal post vaccination reactions
- Light breeds are more susceptible than the heavier ones
- Reactions are more serious after vaccination at days than at 7 days of age because of the lower concentration of circulating antibody
- Vaccination of birds that are immuno-suppressed. Morbid or with compromised respiratory systems
- Use of strong lentogenic or mesogenic vaccine strains for the primary vaccination
- Low level of immunity caused by long intervals between live vaccination
- Poor vaccination technique leaving many birds not immunised
- Live vaccination on multiple-aged laying facilities
- High levels of ammonia and/or duct in the environment
- Poor litter quality
Neurological signs my be seen after the administration of vaccine. One well known example is the post-vaccination encephalitis and encephalopathy following administration of Newcastle disease (R2B) vaccine. The symptoms include torticollis, tremors and limb paralysis. The outcome of neurological involvement may be fatal.
Immuno-suppression is the major immunisation hazard facing the poultry industry at present especially in the case of vaccination against infectious bursal disease (IBD). Administration of intermediate plus (i.e. ‘hot’) vaccines to protect birds from very virulent IBD can result in severe damage to the immune system and immuno-suppression, including sub-optimal responses to vaccines against other disease such as Newcastle disease and infectious bronchitis and hence, vaccination failures. Affected flocks may also show gangrenous dermatitis, necrotic enteritis or coccidiosis during the rearing period. Generally, more virulent strains cause more reaction damage to the immuno system.
Dissemination of contaminants
One of the dangers in the use of vaccines in the dissemination of viruses that contaminate the vaccine. Examples include the adenovirus of egg drop syndrome 1976, recticuloendotheliosis virus and reovirus that have been identified as conaminants in Marek’s disease vaccines.
Rarely causing problems in poultry, many viral vaccines contain traces of various antibiotics used in their preparation and some individual birds may be sensitive to the antibiotic which it contains. Some viral vaccines prepared from animal cell cultures may bring about generalised anaphylactic reactions.
Occasionally following immunisation, there may occur a disease totally unconnected with the immunising agent. The mechanism seem to be that the bird is harbouring the infectious agent and the incubation period and produces disease when what would otherwise only be a latent infection transforms into clinical disease.
Causes include faulty production of vaccine, e.g. inadequate inactivation of the microbe, incomplete sterilisation of injection equipment and microbial contamination. Unsterilised syringes and needles carry staphylococcal and streptococcal infections.
Keys to succesful vaccination, minimising the risk of PVR
- Proper sterilisation of syringes and needles
- Do not vaccinate the birds that are clinically sick or severely debilitated or under severe stress
- Use only vaccines that the manufacturer has thoroughly tested for safety, purity and potency
- Do not break the cold chain from the manufacturer, through transport and storage to administration
- Contamination of the vaccine with other disease-causing agents must be avoided
- Do not use expired or spoiled vaccines and diluents
- Use of hot IBD vaccines is justified only in areas where very virulent IBD, causing 50% losses, is prevalent. Even if the vaccine causes some immuno-suppression, this is preferable to losing hal the flock. ‘Hot’ vaccines have been developed specifically for this purpose but they should not be used unless the highly virulent from of IBD is present.
- Choose approriate vaccine strains
- Follow the instructions on vaccine administration