Comparative pathogenesis of three strains of pseudorabies virus in pigs.

Three strains of pseudorabies virus were intranasally inoculated into 10-week-old pigs and the pathogenesis of the infection was compared. Virulent NIA-3 virus caused widespread necrotic lesions in nasal mucosa, rapidly invading the stroma and infecting axons of olfactory nerves within 24 h of inoculation. Intermediate virulent virus 2.4N3A, a mutant strain derived from NIA-3, caused less necrosis of the mucosa and did not reach axons of olfactory nerves until 72 h after inoculation. Bartha virus strain K, a non-virulent virus strain, caused a mild infection in the superficial layers of nasal epithelium. Viral antigens were not detected in stromal fibroblasts or nerve cells. The inflammatory response of the pigs varied with the virus strains used: after infection with NIA-3 virus mainly neutrophils infiltrated the nasal mucosa, whereas after infection with 2.4N3A virus and Bartha virus, mainly macrophages and lymphocytes infiltrated the nasal mucosa.