Pathogenesis of African swine fever in pigs naturally exposed to the disease

Abstract

Pigs were infected with two virulent strains of African swine fever by housing them for 24 hours with reacting animals at a time when the excretion of virus was known to be at a high level. Virus assay and immunofluorescence tests were conducted on selected tissues of pigs killed 48 to 96 hours after the beginning of contact exposure. Virus was first detected in some tissues at 48 hours after initial contact. Primary infection of the pharyngeal tonsil, followed by extension to the mandibular lymph node, was demonstrated in 9 of 15 animals (60 per cent.). In some instances invasion may have occurred across the nasal, bronchial and, possibly, the gastric mucosae. Generalisation of infection was recorded as early as 48 hours after contact, indicating that some pigs acquired a massive dose of virus. Specific immunofluorescence was detected in lympho-reticular cells of selected lymphoid tissues of the head region, but only after a high virus titre had been attained; no fluorescence was seen in tonsillar epithelium at this time. When virus in the form of a pig spleen suspension was fed to pigs in milk the 50 per cent. infective dose was 10 5·4 HAD 50.