Avian leukosis virus (ALV)
infection in chickens is known to induce increased mortality,
tumors, delayed growth, and suboptimal egg production. Countries importing specified pathogen-free eggs,
vaccines, and poultry breeding stock require freedom of
infection or contamination with ALV in such products among other avian pathogens. Recently, ALV was found as a contaminant in a limited number of commercial poultry
vaccines, even after routine quality assurance procedures cleared the
vaccines for commercialization. The contaminated
vaccines were promptly withdrawn from the market, and no direct detrimental effects were reported in poultry vaccinated with such
vaccines. We describe herein the characterization in vitro of the contaminant viruses. All exogenous viruses detected in four
vaccine lots belong to subgroup A of ALV based on cell receptor interaction, subgroup-specific polymerase chain reaction (PCR), envelope gene sequencing, and virus neutralization. A combination of thermal treatment and serial dilutions of the contaminated
vaccines facilitated detection of contaminating ALVs in cell culture coupled with
antigen-capture
enzyme-linked
immunosorbent assay. Subgroup-specific PCR readily detected ALV-A directly in the contaminated
vaccines but not in naive
vaccines or cell controls. Our methods are proposed as complementary procedures to the currently required
complement fixation for
avian leukosis test for detection of ALV in commercial poultry
vaccines.