Analysis of humoral immunity in broilers challenged with Eimeria prior to and following anticoccidial vaccination, by means of ELISA

BACKGROUND: Despite the use of prophylactic chemotherapy and vaccination, coccidiosis is still one of the most devastating diseases in poultry industry. Understanding the immune mechanism helps researchers to prevent this parasitic infection more effectively. OBJECTIVES: The purpose of this study was to evaluate the antibody response in chickens, induced by a live attenuated vaccine (Livacox Q), before and after challenge, by means of ELISA. METHODS: One hundred and twenty one-day-old male Ross 308 broiler chicks were randomly divided into 4 groups of 30 birds. In 4th day of age, half the birds were orally vaccinated. The challenged groups received the infective dose at 14th day of age via oral administration. Besides recording weight gain, lesion score and oocyst count in 21st day old birds, humoral immunity was assessed by means of ELISA on serum samples taken from 7 and 21day-old birds. Results: Three days post vaccination, the average of optical density (OD) showed significant difference between vaccinated (0.553) and unvaccinated (0.686) birds (p≤0.05). In 21 day-old birds, the OD of unvaccinated-unchallenged (negative control) groups (0.331) differed significantly with vaccinated-unchallenged (0.663) birds. The average of lesion score in vaccinated-challenged birds (2.22) showed significant dissimilarity with unvaccinated-challenged groups. No difference and correlation were observed in comparing average of weight gain and oocyst count with serum optical density among treatment and control groups. ConclusionS: The results indicated that ELISA can be used for evaluating immunity uniformity of a flock after vaccination. Besides inducing antibody responses comparable to challenge with wild oocysts, vaccination with live attenuated coccidiosis vaccines may have inhibitory effects in intestinal lesion scores which are responsible for pathogenesis and economic loss during coccidial infections.