Avian Encephalomyelitis in Layer Pullets Associated with Vaccination.

Area of Science:

• Veterinary Virology
• Avian Pathology

Background:

• Avian encephalomyelitis (AE) is a contagious viral disease affecting young poultry.
• Vaccination is a common strategy to prevent AE in commercial flocks.

Observation:

• Three flocks of leghorn layer pullets (11-14 weeks old) in California exhibited clinical signs suggestive of AE post-vaccination.
• Signs included neurological deficits (recumbency, lethargy), poor growth, and mild to moderate mortality.
• Birds were vaccinated with a combined fowl pox and AE vaccine 2 weeks prior to symptom onset.

Findings:

• Histopathology revealed characteristic AE lesions in the brain and spinal cord.
• Avian encephalomyelitis virus was confirmed by RT-PCR and virus isolation from affected birds.
• Other potential neurotropic viral causes of encephalitis were excluded through diagnostic testing.

Implications:

• This case series highlights the potential for AE to occur despite vaccination, necessitating further investigation into vaccine efficacy or field challenges.
• Accurate diagnosis is crucial to differentiate AE from other encephalitic diseases in poultry.
• Understanding post-vaccination AE outbreaks informs vaccination strategies and disease management in commercial poultry operations.