Selection and characterisation of two attenuated vaccine lines of Eimeria tenella in Australia.
OBJECTIVE
To attenuate two strains of Eimeria tenella by selecting for precocious development and evaluate the strains in characterisation trials and by field evaluation, to choose one precocious line for incorporation into an Australian live coccidiosis vaccine for poultry.


METHODS
Two strains from non-commercial flocks were passaged through chickens while selecting for precocious development. Each strain was characterised for drug sensitivity, pathogenicity, protection against homologous and heterologous challenge, and oocyst output in replicated experiments in which the experimental unit was a cage of three birds. Oocyst output and/or body weight gain data collected over a 10 to 12 day period following final inoculation were measured. Feed conversion ratios were also calculated where possible.


RESULTS
Fifteen passages resulted in prepatent periods reduced by 24 h for the Redlands strain (from 144 h to 120 h) and 23 h for the Darryl strain (from 139 h to 116 h). Characterisation trials demonstrated that each precocious line was significantly less pathogenic than its parent strain and each effectively induced immunity that protected chickens against challenge with both the parent strain and other virulent field strains. Both lines had oocyst outputs that, although significantly reduced relative to the parent strains, remained sufficiently high for commercial vaccine production, and both showed susceptibility to coccidiostats.


CONCLUSIONS
Two attenuated lines have been produced that exhibit the appropriate characteristics for use in an Australian live coccidiosis vaccine.
Agency for Food and Fibre Sciences, Department of PrimaryIndustries, Animal Research Institute, Locked Mail Bag No. 4, Moorooka, Queensland 4105.
W K
WK
Jorgensen
G R
GR
Anderson
P J
PJ
Jeston
G W
GW
Blight
J B
JB
Molloy
D000818:Animals; D001315:Australia; D001835:Body Weight; D002645:Chickens; D003048:Coccidiosis / Q000517:prevention & control / Q000662:veterinary*; D016786:Eimeria tenella / Q000276:immunology* / Q000472:pathogenicity; D005243:Feces / Q000469:parasitology; D010270:Parasite Egg Count / Q000662:veterinary; D011201:Poultry Diseases / Q000517:prevention & control*; D016052:Protozoan Vaccines / Q000276:immunology*; D014613:Vaccines, Attenuated / Q000276:immunology; D014774:Virulence
D016052:Protozoan Vaccines; D014613:Vaccines, Attenuated