Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/1999
Publication Date: N/A
Citation: Interpretive Summary: Marek's disease is an important viral disease of chickens which is characterized by the development of tumors composed of lymphocytes, a type of white blood cell. Although these tumors occur in many body tissues, the brain is usually not affected. Results of this paper establish that the brain can be an important site of this disease. Four distinct types of brain-related clinical disease are described in chickens of two genetic types after inoculation with hot strains of Marek's disease virus. The development of changes in the brain during each of these forms is also described. These findings may help scientists classify different strains of Marek's disease virus more quickly than with conventional methods. The data also suggest that more work on the brain in chickens with Marek's disease would help our understanding of the disease and ultimately aid in its control.
Technical Abstract: The present study was designed to elucidate the pathogenesis of neurological syndromes induced by highly virulent MDVs in chickens of two genetic lines inoculated at three weeks of age. In the first experiment four distinct neurological syndromes were identified, two of these for the first time. Classical TP was characterized by a sudden onset of paralysis at about 9 days post inoculation (dpi) that totally disappeared in 2-3 days. Acute TP began at 8-9 dpi and resulted in death usually within 48 hours. Persistent neurological disease (PND) designates birds which showed a variety of neurological signs after recovery from paralysis (12-15 dpi), that either persisted through the observation period or presented a cyclical pattern. Late paralysis (LP) was a rare syndrome characterized by the late onset of the paralytic stage (about 20 dpi). In the second experiment, clinical signs and histopathological alterations of the brain were evaluated sequentially in chickens of two genetic lines after inoculation with two MDV strains (v and vv+). Regardless of chicken line or virus strain, similar types of lesions appeared in 70% of the brains. Analysis by treatment group showed that clinical sign development was related to the early onset and persistence of lesions. The frequency of clinical responses was also greatly influenced by viral pathotype (or virulence) and chicken strain in both experiments. These studies confirm that the central nervous system is an important target organ for MDV and suggest that neurological responses in antibody-free chickens may be useful indicators of viral virulence and genetic resistance.