Immunosuppressive effects of the Indian isolate of chicken anaemia virus (CAV) in specific pathogen free chicks*

The present study was carried out to find out the immunosuppressive effects of an Indian isolate of chicken anaemia virus (CAV) in experimentally infected specific pathogen free (SPF) chicks. Briefly, out of 110 day-old SPF chicks, sixty chicks (group I - 40, group II - 20 chicks) were inoculated with 0.5 ml of 10^4,5 TCID₅₀/0.1 ml of CAV isolate while twenty chicks were kept as NOV control (group III) and thirty chicks served as absolute control (group IV). Twenty chicks each of Group II and III received NOV-F vaccination (10^6,5 EID₅₀/chick) occulonasally at one week of age. CAY infected groups showed characteristic signsand lesions of disease. Chicks of the groups II and III were monitored for the effect on humoral immune response by assaying ND-HI antibody titres and cell-mediated immune response by assessing lymphoproliferative responses of peripheral blood mononuclear cells at weekly intervals viz. 1st, 2nd, 3rd and 4th week post vaccination (WPV). Chicks of group II showed significantly lower (P<0.01) ND-HI titres at 1 WPV than the group III chicks throughout the observation period. The highest geometric mean HI titre of only 21.08:1:1.46 was recorded in the group II whereas a maximum titre of 146.89:1:1.36 was observed in the group III at 2nd WPV. Similarly, the lymphoproliferative responses, on in vitro stimulation with Con-A mitogen and NOV-F antigen, were significantly reduced (P<0.01) in group II chicks at 1–3 WPY with maximum reduction at 1st WPV. Microscopic changes in the lymphoid organs and significant reduction (P<0.01) in lymphoid organ (thymus, bursa and spleen) to body weight ratios also revealed the immunosuppressive potential of the virus. The marked suppression of both humoral and cell-mediated immune responses indicated the potential immunosuppressive nature of the virus.