[Experimental vaccines against avian inclusion body hepatitis. I. Serological evaluation]

Two Inclusion Body Hepatitis (IBH) vaccines (Vac-19 and Vac-28) were elaborated from serotypes 4, 10 and 11, isolated from country field outbreaks. The strains were attenuated by passages in embryonating SPF chicken eggs (16 and 22 passages for both vaccines) and in kidney cell culture (3 and 6 passages respectively). Four experimental groups (G) were used: G I and G II of 8 chickens each, vaccinated orally (4,4 TCID50/ml) with Vac-19 and Vac-28 respectively, at the third week and re-vaccinated 35 days later with the same dose and method. Groups G III and G IV with 5 chickens each were the positive and negative controls, both group were not vaccinated, the first only challenged wit a pool of the 4, 10 and 11 serotypes on 45 days old and the last was not challenged. Prior and afterward, vaccination and challenge, clinical and serological exams were performed. The immune response was determined trough Agar Gel Precipitin (AGP) and serum neutralization (SN) test in chicken kidney cells (CKC) using the beta method (200 TCID50/50 microliters). Positive response (100%) was detected from day 43 onward in the vaccinated group, to AGP test. This situation occurred on day 55 for the challenged group (G III). Geometric mean titres (GMT) were, prior to challenge, 1.194 for G I and 23.525 for G II. After challenge, GMT were 7.760 and > or = 305.736 respectively. The GMT for G III was 640. No clinical signs or mortality were observed during the experiment. The conclusion is that only Vac-28 provided a partial protection to the fowl, measured through the lesions observed.