Location: Endemic Poultry Viral Diseases ResearchTitle: Immune-tolerance mediated neuropathogenicity of Marek's disease vaccines
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/14/2020
Publication Date: N/A
Technical Abstract: We identified an acute neuroparalytic syndrome similar to transient paralysis in chicks infected in ovo with a Meq-deleted strain of MDV during the thymic tolerizing window (11 to 14 days of embryonation); injection on EID11 resulted in 70% mortality from acute paralysis. In contrast, chicks infected post-hatch with this strain showed 0% morbidity and mortality. As expected, Meq-deleted Md5 alone did not produce visceral tumors or nerve enlargements in any birds regardless of infection time, indicating that tolerance-mediated neuropathogenicity was not due to oncogenic potential, but rather indicative of retained neurovirulence of this virus when not effectively controlled by adaptive immunity. We additionally tested commonly used vaccine strains and found 13% incidence of acute paralysis from HVT tolerization and 20% incidence of acute paralysis in CVI/Rispens-tolerized birds, and affected birds showed perivascular infiltrates within the brain, similar to acute transient MD; toleration with SB-1 did not cause acute paralysis. These findings indicate that current attenuation strategies for some Marek's vaccines have not removed viral tropisms for central nervous tissues, and immunosuppression may be sufficient to allow vaccine-mediated MD neuropathy to occur.