Live Vaccines

Live non-attenuated vaccination exploits the limited parasite reproduction of a live organism and the host’s ability to naturally reduce clinical signs of Eimeria infection. In other terms, live vaccines stimulate the immune response of the host with no clinical or subclinical pathogenic effects with limited parasite reproduction and minimal oocyst output. To induce protective immunity for a mixed Eimeria species infection, birds have to be given at least two or more exposures to the specific parasite (1).  With vaccination, the first exposure comes from the oocysts in the vaccine dose and the second exposure comes from cycled oocysts via fecal-oral transmission. Once this protective immunity is developed for a certain Eimeria species the bird is immune against further infection with this particular parasite (1). The number of oocysts in the initial vaccine dose determines the number of oocysts that will be cycled. With all live coccidiosis vaccines, there is a fine balance between giving sufficient parasites with cycling to reduce clinical signs versus having so many cycling parasites that intestinal lesions are formed.

There are two main factors needed for a live vaccine to reach its full protective potential (2):

1)      Vaccine administration - synchronous, uniform vaccine oocyst ingestion

Commonly spray vaccination is used in the hatchery at day of hatch. The spray cabinet will spray a coarse, high volume, coloured spray either made up of water or gel droplets over a batch of chicks. 

2)      Environment control in the barn - adequate controlled low-level oocyst cycling

Environmental control in the barn can be separated into two sections:

a)      Physical environment – including where the birds are housed (e.g. litter, conventional cage, alternative system).

b)      Atmospheric barn environment – including temperature, relative humidity and oxygen access (see Management through the environment).

Intimately knowing your housing system and each barn’s atmospheric environment can help you manipulate oocyst cycling and, proactively managing these factors is likely to improve live vaccine success. 

Please consult your veterinarian and vaccine company representative for information specific to the vaccine and vaccine management system being used on your farm.

References

1. Chapman, H.D. Practical use of vaccines for the control of coccidiosis in the chicken. World's Poultry Science Journal 56:7-20. 2000.

2. Price, K.R. Use of live vaccines for coccidiosis control in replacement layer pullets. Journal of Applied Poultry Research 21:679-692. 2012.