Avian Encephalomyelitis in Layer Pullets Associated with Vaccination

Abstract

Avian encephalomyelitis (AE) was diagnosed in three flocks of leghorn layer pullets following AE vaccination. Ages of the birds were 11, 12, and 14 wk. The submissions came from three different companies located in two geographic areas of the Central Valley of California. The clinical signs included birds down on their legs, unilateral recumbency or sitting on their hocks, lethargy, reluctance to move, dehydration, unevenness in size, low weight, tremors of the head in a few birds, and mildly to moderately elevated mortality. The flocks had been vaccinated against fowl pox and AE with a combined product in the wing-web 2 wk prior to the onset of AE clinical signs. Histopathologic examination revealed lesions consistent with AE, including lymphocytic perivascular infiltration and neuronal central chromatolysis in the brain and spinal cord, as well as gliosis in the cerebellar molecular layer. The AE virus was detected by reverse-transcriptase PCR in the brain homogenate from three cases and peripheral nerves in one case. Additionally, the AE virus was isolated in specific-pathogen-free (SPF) embryonated eggs from brain tissue pool samples. Other avian viral infections capable of causing encephalitis, including avian paramyxoviruses, avian influenza virus (AIV), West Nile virus (WNV), eastern equine encephalitis virus (EEEV), and western equine encephalitis virus (WEEV), were ruled out by attempting virus isolation and molecular procedures.

Assessing the efficacy of a live vaccine against avian encephalomyelitis virus

“…Among the 667 clinical samples tested, seven were positive for AEV, and two AEV strains were isolated and designated as GDt29 and GD-S-29, respectively. This is consistent with previous reports [7,12,19], that AEV continues to be present in the poultry industry.…”

“…Breeder flock vaccination programs designed to provide progeny with maternal antibodies can result in better performance of progeny and prevent transovarian transmission during the period of greatest susceptibility 1-3 weeks after hatching [10]. In China, vaccination is mainly done in 14-to 16-week-old breeders by administering a live field virus by the natural route of infection in their drinking water, or by wing-web inoculation through intracutaneous injection [10][11][12][13]. This immunity not only protects hens during laying but also protects their progeny through maternal antibodies [4,14].…”

Avian Viruses that Impact Table Egg Production

“…In young chickens, the neurological nature of the disease involves clinical signs, such as ataxia, paralysis, and tremors [ 92 ]. However, clinical AE has been encountered in layer pullets following the application of live AE vaccines [ 93 , 94 ]. Naturally occurring outbreaks have also been identified in pheasants, quails, pigeons, and turkeys [ 95 ].…”

Field safety and efficacy of a unique live virus vaccine for controlling avian encephalomyelitis and fowlpox in poultry

“…Avian encephalomyelitis (AE) and fowlpox (FP) are two of the common viral diseases of poultry worldwide. Although AE virus primarily infects chickens, the virus has also been isolated from other avian species including turkeys and quail [1-3]. The avipoxviruses, on the other hand, have been isolated from numerous avian species including chickens, turkeys, canaries, flamingo, and others [4-12].…”

“…Integration of reticuloendotheliosis virus genome sequences of various lengths in the FP virus genome has been reported to enhance the pathogenicity of the virus resulting in the emergence of the very pathogenic or variant strains of the virus [13]. The AE virus infection in laying and breeding flocks causes a marked drop in egg production, decrease in egg hatchability, and high mortality in young infected chicks [1-3]. To control these two diseases, poultry producers routinely vaccinate their flocks with AE and FP live virus vaccines [14-19].…”