Infection of Microtus arvalis (common vole) with Mycobacterium tuberculosis and Mycobacterium bovis

The aim of the study has been to ascertain whether Microtus arvalis (common vole) is strongly susceptible to M. bovis but resistant to M. tuberculosis, as is the case with other members of the vole family, or whether it is susceptible to both species as demonstrated by Robert Koch. Groups of common voles have been injected subcutaneously or intraperitoneally with varying doses of finely dispersed suspensions of a virulent strain of M. bovis or M. tuberculosis. M. bovis multiplies strongly in the vole organism and a dose as small as 8 viable units provokes a progressive infection with rapid fatal outcome. Autopsy shows considerable processes at the site of injection and in the lymph glands. Tubercles are observed quite frequently in the lungs, bur seldom in the liver, spleen and kidneys. The organs contain a large number of tubercle bacilli, the caseous lymph glands enormous numbers. In contrast, the virulence of M. tuberculosis is low. None of the doses used, the highest being 6 x 10(6) viable units, provokes progressive infection in the animals injected subcutaneously and only in a few of those injected intraperitoneally. The macroscopical findings are inconsiderable, and it is characteristic of the M. tuberculosis infection that the lymph glands are seldom enlarged and have become caseous in exceptional cases only. The number of bacteria in the organs is small, except in the few animals in which the infection becomes progressive. The conclusion drawn from the experiment is that Microtus arvalis is susceptible to M. bovis but strongly resistant to M. tuberculosis, and in this respect resembles other members of the vole family examined hitherto.