Files
Abstract
In the past few years, NDV strains belonging to sub-genotypes VIIi and XIIIb have emerged in the Middle East and Asia, where they co-circulate with pre-existing genotypes. Strains of sub-genotype VIIi have epizootic characteristics, spreading rapidly in different regions with high mortality. In this study two NDV strains, one representative of sub-genotype VIIi isolated in Israel (APMV1/Broiler-Breeders/Israel (Kvuzat-Yavne)/NDV/826/2013 [Kvuzat/13]) and one representative of sub-genotype XIIIb isolated in Pakistan (APMV1/chicken/SPVC/Karachi/NDV/33/2007 [Karachi/07]), were characterized by intra-cerebral pathogenicity index (ICPI) and detailed clinico-pathological assessment. The ICPI values for Kvuzat/13 and Karachi/ 07 were 1.89 and 1.85, respectively, classifying these strains as virulent NDV by international standards. Groups of 4-week-old, White Leghorn chickens were inoculated in the right conjunctival sac and choanal slit with 105.5 Embryo Infectious Dose 50% (EID50) units of virus. Viruses caused 100% mortality within 4 days (Kvuzat/13) and 5 days (Karachi/07) post infection. Gross and histologic lesions in all infected birds included: severe hemorrhagic conjunctivitis, extensive necrosis of lymphoid tissues, segmental necrosis, and hemorrhage in the small and large intestine. As shown by immunohistochemistry for NDV nucleoprotein, intense positive signal was observed in the lymphoid organs (spleen, bursa, thymus), the mucosa-associated lymphoid tissue in the intestine (cecal tonsils) and the respiratory tract (larynx), trachea, and Harderian glands. In lymphoid organs, immunohisotchemical signal was observed mainly in macrophages, while in the trachea and Harderian gland was observed also in epithelial cells. Results of the animal experiment confirm that both Kvuzat/13 and Karachi/07 are highly virulent and behave as velogenic viscerotropic NDV strains.