[Various mechanisms of formation of chronic tularemia in highly-sensitive animal species (Microtus rossiae-meridionalis)].

Experiments on voles belonging to the tularemia-sensitive species Microtus rossiae-Meridionalis, infected with Francisella tularensis highly virulent strain 503, have been carried out with the aim of studying the pathogenesis of chronic tularemia. The experiments have been made with the use of live and killed microbial cells. The significance of the multiple oral administration of killed bacteria to voles for the development of the atypical form of infection has been shown. The possibility of the early (on day 2) formation of antibodies in the blood of some of the animals has been established. Repeated feeding has been found to lead to almost 100% seroconversion in the animals. This fact can be attributed to the rapid spread of the antigen (1-5 hours) in the organs of individual animals. Besides, the causative agent is present in large amounts in lymphoid formations of the intestinal tract and in the lumen of the intestine, which creates conditions for the early contact of the massive dose of the antigen with immunocompetent cells and for the rapid development of systemic and local immune response. Morphological study indicates the presence of the rapid (24 hours) proliferative reaction of the cells making up the lymphoid apparatus of the intestine, their plasmocytic and macrophagal transformation. Thus, after the infection of voles with a mixture of live and killed bacteria the development of the early phases of the infectious process occurs simultaneously with the systemic and local transformation of the macroorganism, which contributes to the benevolent course of the infectious process in some of the animals.