Comparison of the onset of an immune response using three oocyst vaccination strategies

D.G. Richards*, Eimeria Research Project, Werribee, Australia
*medichick@ava.com.au

EimeriaVAX 4mŽ is a 4 species coccidiosis vaccine containing Australian precocious strains of E acervulina, E maxima, E necatrix and E tenella administered to 100% birds by individual eye-drop application from day-old. Aerosol spray is appealing because it is less time-consuming for mass application of oocysts. Unfortunately, aerosol is not as precise. There is no information on whether the alternative of eye drop vaccination of a percentage of chickens plus coarse aerosol spraying the remainder would overcome the reduced accuracy of aerosol. To investigate this hypothesis, three groups of broilers were vaccinated at day-old with a) 100% coarse aerosol, b) 15% individual eye-drop and 85% aerosol and c) 100% individual eye-drop. One group of birds was unvaccinated. Oocysts per gram of faeces (OPG) were enumerated for each group at 5, 6, 7, 14, 21, 28, 35, and 42 days of age. At 11, 20, and 29 days post-infection, birds were removed and challenged with live oocysts of the same species in the vaccine. At 6 days post challenge, intestinal tissues were fixed. Following histological preparation and staining, tissues were scored for lesions. Weight gain post challenge was collected.
At 5, 6 and 7 days post vaccination there was a spike in the OPG from the group vaccinated at day-old by eye-drop. Following the first challenge at 11 days of age, comparative analysis of the OPG showed eye-drop vaccinated chickens always showed the lowest OPG for each day. This trend was repeated with the histological analysis. Following the challenge at 20 and 29 days of age, OPG results indicated that the challenged groups had the highest oocyst output, the highest histological lesion scores and the lowest weight gain. There was no consistent difference between any vaccination regime.
The results show the immune response by 10 days post vaccination was sufficient to give the birds vaccinated by eye-drop some protection from challenge. There was no difference between any groups by 21 days. It is concluded there is a delay in the onset of immunity when administering live coccidiosis vaccines by aerosol spray. This paper also describes the success of the in field use of the aerosol and eye-drop technique.