Newcastle Disease Virus VII.2 First Record in Kazakhstan

Abstract

Although the NDV vaccination program is quite intensive in Kazakhstan, disease outbreaks are occurring repeatedly. During the fall season of 2023, we effectively achieved the isolation of the Newcastle Disease Virus (NDV) specifically, the class II genotype VII.2. This was accomplished in the context of an outbreak within industrial poultry layers located in the northern geographical sector of Kazakhstan. The employed methodology encompassed an exhaustive phylogenetic analysis of the fusion protein gene. This rigorous analytical process led to the definitive classification of the isolated virus under the category of NDV class II genotype VII.2. Yet the outbreak occurred despite highly qualitative on-farm vaccination against NDV. The study revealed that during the outbreak, serologic testing using both the Hemagglutinin Inhibition test (HI) test showed an increase of antibody titers in old layers (10,3±2,6 log₂) and contrarily the fall of protective antibodies in young layers (5,2±1,8 log₂), notwithstanding that before the outbreak, HI titers in all groups of layers were similar and amounted 8 log₂. Moreover, we conducted a pathological and microscopic examination of dead layers. We observed necrotic lesions, extensive hemorrhages, and congestion in various internal organs, indicating the infection with NDV virulent form. Histological analysis revealed vascular inflammation in the skin, eosinophilic endovasculitis, esophageal mucous membrane inflammation, larynx epithelium necrosis, and severe laryngeal swelling. This study highlights the first proven case of the VII.2 NDV strain in industrial birds in Kazakhstan, shedding light on the recurring outbreaks despite intensive vaccination. Veterinarians can use this information to detect NDV outbreaks early among vigorously vaccinated industrial birds.