Postural and Neurological Deficits in Broiler Chicks after Cervical Vaccination with Live Vaccine

Abstract

Abstract.A disease characterized by paresis and paralysis was seen in 7-9-day-old broiler chicks after vaccination in the neck area at day-of-age with a live virus vaccine containing viruses of Marek's disease, fowl pox, and infectious bursal disease. Affected birds presented with variable signs of ataxia, lateral recumbency, leg paralysis, and twisting or S-shaped flexure of the neck. Gross lesions noted at necropsy included swelling and edema of the subcutaneous tissues and muscles of the neck at the injection site area. A heavy mononuclear inflammatory cell infiltration was seen in the subcutaneous tissues, connective tissues, and muscles of the neck at the injection site. In some cases, the inflammatory process extended along fascial planes to involve the epidural spaces surrounding the spinal cord. Fatty changes with possible demyelination of nerve fibers were noted in some sections of the spinal cord adjacent to the inflammatory lesions. Clusters of poxviruses were found within some inflammatory lesions on transmission electron photomicrographs.A total of 8 separate submissions of broiler chicks showing twisting or S-shaped flexure of the neck, ataxia, lateral recumbency, and various degrees of paresis and paralysis were made to the Turlock branch laboratory of the California Animal Health and Food Safety Laboratory System, beginning in 1995. Morbidity and mortality rates in the 7-9-day-old chicks approached 6% or more in some affected flocks, primarily because of dehydration and starvation. Within 3-4 days of the onset of the problems, most affected birds either died or were culled out. All affected birds had originated from the same hatchery, where they had been vaccinated in the neck area at day-of-age with a live virus vaccine containing Marek's disease (MD) virus, including SB-1 and turkey herpes virus (THV), fowl pox (FP) virus, and infectious bursal disease (IBD) virus. Penicillin, streptomycin, and fungizone were added to the vaccine as preservatives. Necropsy findings included swelling and edema of the subcutaneous tissues of the neck area, with yellowish discoloration and occasional petechial hemorrhages in affected tissues. Inflammation of the subcutaneous tissues, muscles, and connective tissues of the neck was evident, with a heavy infiltration of lymphocytes, macrophages, and reticular cells (Fig. 1). In some cases, the inflammatory process extended along fascial planes to involve the epidural spaces surrounding the spinal cord (Fig. 2). Cellular enlargement and vacuolization of epithelioid cells were noted microscopically in some areas of the inflammatory process (Fig. 3). Clusters of viral particles with typical poxvirus morphology were noted within some lesions on electron photomicrographs (Fig. 4). shown) were noted in some areas of the spinal cord adjacent to the mass of inflammatory cells occupying the epidural space.Attempts were made to isolate bacteria from the subcutaneous tissues of the neck at the injection site area and from the brain and liver tissues of affected birds. No bacte...