Hydatidosis Disease: The correct amount of vaccine protein and adjuvant
The correct amount of the antigen to make a suitable vaccine needs to be determined. It is necessary to carry out dose-response trails on the amount of antigen and also on the amount of adjuvant, once a decision has been made on the adjuvant available, many of which are registered for veterinary use.
A test of a number of adjuvants showed that Quil A (Brentag Nordic) was superior in its ability to promote the highest level and longest persistence of protection against a challenge infection with eggs of E. granulosus, while causing minimum host reaction at the injection site. The amount of antigen and amount of adjuvant produce additive effects up to a certain safety margin.
We have found that the most effective amount of antigen is in the region of 50 µg of active molecule and best responses are obtained with 1mg of Quil A for sheep and goats. The dose-rate for mature bovines is five times that recommended for sheep.
Formulation of the Vaccine
Because Quil A is hydrolysed in alkaline conditions the vaccine has to be formulated in a slightly acid environment. The vaccine must withstand freeze-drying and reconstituting so that the product will have a good shelf-life and can be distributed to the field in a form which will maintain activity under sometimes less-than-perfect conditions. The formulated vaccine is sterilefiltered into sterile vials, and freeze-dried.
Quality control and sterility testing is carried out on the freeze-dried product, using bacteriological and biochemical tests and immunization of sheep. It is important that the vaccine has at least a 12-month shelf-life at 4C.
All production batches should be individually tested for potency in target animal trials. Potency is proven by monitoring the serological response of sheep in comparison with serum from immunized and protected sheep. The serological responses of a new batch of vaccine are normally tested in ten vaccinated animals.
The vaccine passes the test if eight of the vaccinated animals show a serological response which is equal to or exceeds the serological response of fully protected vaccinated animals. The recommended storage temperature is 4C but the vaccine will retain better activity if stored at-20C, and has an indefinite shelf-life when stored at -80C. The sterile diluent (buffered saline at pH 6.8) which is used for diluting the freeze-dried vaccine should be sent with the vaccine. Any unused reconstituted vaccine should be stored at -20C for no longer than 1 month.