Pathogenesis of conjunctivitis caused by Newcastle disease viruses in specific-pathogen-free chickens

The pathogenesis of conjunctivitis caused by Newcastle disease viruses (NDVs) was investigated in 3-week-old specific-pathogen-free chickens. The chickens were inoculated intramuscularly, by eye drop or intranasally, with 10(7) plaque forming units of viscerotropic velogenic Newcastle disease virus (VVNDV), mesogenic NDV or lentogenic NDV. Macroscopically, lower palpebral conjunctivae appeared red with oedematous swelling in chickens inoculated with VVNDV. Histologically, mild lesions were focal hyperplasia of the conjunctival epithelial cells with cellular infiltration in the lamina propria of the conjunctivae in the chickens inoculated with VVNDV. Moderate lesions were vascular necrosis with congestion and haemorrhages, hyperplasia of conjunctival epithelial cells, and oedema and cellular infiltration in the lamina propria of the conjunctivae. Fibrin thrombi were observed in the capillaries of the lamina propria. In marked lesions, the whole conjunctiva was affected with more severe and extensive lesions. The mesogenic and lentogenic NDV strains induced no gross conjunctival lesions, but induced mild conjunctivitis without vascular necrosis.