Marek's Disease in France: Ten Cases of Central Nervous System Syndromes.

Between 2017 and 2019, 10 broiler flocks, with birds exhibiting neck paralysis, nervous tics, and torticollis, were submitted for necropsy and additional tests. These neurologic signs were mostly observed in certified, nonvaccinated broilers (8 of 10), ranging between 45 and 56 days of age. No specific lesions were described at macroscopic examination. Histopathology revealed moderate to severe lymphocytic infiltration of the central nervous system (CNS). In addition, peripheral nerves and visceral organs were commonly affected, although less severely. Immunohistochemistry identified the infiltrating lymphocytes as CD3+ T cells, and Marek's disease (MD) virus was detected by real-time PCR in brain formalin-fixed and paraffin-embedded samples in all flocks. In conclusion, MD is still a concern in France. The occurrence of MD CNS syndromes should be considered in commercial broilers starting from 6 wk of age because these conditions could compromise the health and welfare of affected birds. Poultry veterinarians should be aware of this atypical form of MD to ensure proper diagnosis and assess the impact of the disease, especially in nonvaccinated chicken flocks.