Vaccination-challenge interval markedly influences protection provided by Rispens CVI988 vaccine against very virulent Marek's disease virus challenge.

Vaccination-challenge interval markedly influences protection provided by Rispens CVI988 vaccine against very virulent Marek's disease virus challenge.
Avian Pathol. 2013 Oct 7;
Authors: Islam T, Walkden Brown SW, Renz KG, Fakhrul Islam AF, Ralapanawe S
Abstract
The Rispens (CVI988) vaccine is widely used to vaccinate chickens worldwide. We tested the protective effects of the Rispens vaccine against challenge with very virulent Marek's disease virus (vvMDV) at various intervals at, before or after vaccination. The experiment used commercial ISA Brown layers and vvMDV isolate 02LAR. The protective index (PI) was measured for vaccination challenge intervals (VCI) of -10, -5, 0, 5 and 10 days, with the negative values indicating challenge prior to vaccination. Chickens were challenged by injection with 400 plaque-forming units (PFU) of 02LAR and/or vaccinated with 3200 PFU of the Rispens vaccine virus at days 0, 5 and 10 of age, with appropriate negative controls injected with diluent only. The presence of visible Marek's disease tumours was assessed up to 56 days post challenge. MDV challenge in unvaccinated chickens resulted in tumours in 52% of chickens. The Rispens vaccine provided no significant protection when challenge preceded vaccination, with PIs of -4 and 21% for VCI of -5 and -10 days respectively. On the other hand, it provided PIs of 60, 85 and 100% at VCI of 0, 5 and 10 days respectively. The study also revealed that the vvMDV loa...

Source: Avian Pathology - October 7, 2013 Category: Pathology Authors: Islam T, Walkden Brown SW, Renz KG, Fakhrul Islam AF, Ralapanawe S Tags: Avian Pathol Source Type: research