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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Endemic Poultry Viral Diseases Research » Research » Research Project #440103

Research Project: Effect of Marek’s Disease CVRM Vaccine on the Enhancement of Spontaneous Avian Leukosis-like Tumors

Location: Endemic Poultry Viral Diseases Research

Project Number: 6040-32000-083-012-A
Project Type: Cooperative Agreement

Start Date: Apr 1, 2021
End Date: Feb 28, 2026

Objective:
Spontaneous bursal lymphomas of unknown etiology have been reported in chicken lines and crosses that have been maintained in specific pathogen free (SPF) conditions that are free of exogenous retroviruses (Crittenden et al., 1979). The Avian Disease & Oncology Laboratory maintains a genetic line of chickens, Line ALV-6, that is prone to a small incidence of spontaneous tumors. Using this line, past studies have demonstrated that the serotype 2 MDV strain SB-1 is responsible for increased incidence of spontaneous bursal lymphomas in this line (Salter et al., 1999). This enhancement was later confirmed by elimination of SB-1 vaccination in this line, and also shown to occur whether SB-1 was administered in ovo or at hatch (Cao et al., 2015). Given the recent increase in use of a new generation of Marek’s disease vaccines and new MD-based vaccine vectors, there is renewed interest in confirming that these new MD vaccines do not similarly enhance spontaneous bursal lymphomas. One recently developed MD vaccine, CVRM, is a serotype 1 recombinant vaccine based on CVI988 with insertion of reticuloendotheliosis virus LTR (Lupiani et al., 2013). This proposal aims to evaluate whether the CVRM vaccine causes enhancement of spontaneous avian leukosis-like tumors in Line ALV-6 chickens. Current objectives include: 1. Evaluate the effect of MDV vaccine CVRM, a serotype 1 vaccine, on enhancement of spontaneous tumors. 2. Compare effect of CVRM vs. SB-1 and CVI988.

Approach:
In this experiment, ALV-6 birds will be used. Fifty birds per group will be vaccinated at hatch with 2000 pfu of SB-1, CVI988 or CVRM. All birds will be housed at Michigan State University for duration of experiment. At 4 weeks, feathers from 10 birds per vaccinated group will be collected to measure vaccine replication kinetics. At 8 weeks, 5 birds per group will be removed and bursa samples collection for immune profiling. At 10 weeks, all birds from vaccinated groups will be bled for measuring vaccine virus. At 52 weeks, birds will be terminated for necropsy and identification of spontaneous tumors.