The pathology of untreated and antibiotic-treated experimental tularaemia in monkeys.

Grivet monkeys were infected intranasally with the virulent Schu-S4 strain of F. tularensis. One group of animals remained untreated and two other groups received a 7-day course of kanamycin therapy starting on either the third or fourth day after infection. Untreated monkeys developed pyrexia and mucopurulent oculonasal discharge and died 5--7 days after infection. All had pyogranulomatous lesions in the liver, spleen, respiratory tract and lymph nodes. Electron microscopy of liver and spleen showed phagocytosis of F. tularensis organisms by macrophages and polymorphonuclear leucocytes, but many bacteria survived phagocytosis and were released on destruction of the cells. Kanamycin therapy enabled most monkeys to survive the disease, but it did not prevent the development of persistent lesions in all animals. Caseous nodules were larger and more widespread in the organs of monkeys in which treatment was delayed until the fourth day of infection.