Comparative immunological and genomic characterization of fowlpox virus isolates

Chickens infected with fowlpox virus (FPV) IVRI vaccine strain and two field isolates collected from clinical cases of disease (Bareilly isolate and Panchmahal isolate) produced humoral antibody response after 2nd week post-infection, with a noticeable variation in degree of immune response. Serum antibody titre peaked at 4th week post-infection with a titre of 25,600, 25,600 and 51,200 being detected in ELISA and neutralization index of 2.75, 2.43 and 3.12 in serum neutralization test (SNT) with IVRI vaccine strain, Panchmahal isolate and Bareilly isolate, respectively. Cellular immune response was detected as early as 1st week post-infection by leukocyte migration inhibition test (LMIT). Per cent migration inhibition too peaked at 4th week with a value of 40.30 +/- 3.45, 36.93 +/- 4.11 and 45.45 +/- 3.66 being detected with the three viruses respectively. The Hind III and Hae III restriction fragment profile of viral DNA showed almost similar pattern both in vaccine strain and two field isolates. Hind III digestion produced 47 well resolved fragments of sizes between 24.30 and 1.20 kb and the total genomic size was estimated to be between 305.81 and 306.06 kb. Hae III digestion revealed 34 well resolved fragments of sizes between 27.55 and 1.32 kb. The three viruses could not be differentiated on the basis of their genomic restriction pattern. However immunogenic and antigenic differences were noticed by ELISA and SNT tests.