Virulence of five isolates was investigated in golden hamsters (Mesocricetus auratus) line HAN:AURA. In the first experiment, 24 hamsters were infected with Mycobacterium avium subsp. paratuberculosis (MAP) cattle isolate of RFLP type B-C1 from a herd with a rapid spread of infection. Hamsters were infected per os (po), subcutaneously (sc), and intraperitoneally (ip), per eight animals in each group. Shedding of the causative agent through faeces was monitored for 7 months; after euthanasia the gastrointestinal tract was examined. Excreting of MAP of identical RFLP type was induced by all routes of infection and was observed during the whole period of the experiment. In the following experiment performed for 32 months, 96 hamsters were infected with four MAP isolates of three RFLP types: B-C1 from larvae of syrphid flies and from a patient with Crohn's disease (CD), A-C10 from cattle with a slow spread of infection, and D-C12 from a CD patient. Faeces were cultured on solid Herrold's egg yolk medium and liquid Long medium with Mycobactin J. The hamsters survived in average for 20.5 months (range 5-32 months). No signs of chronic diarrhoea or emaciation were recorded. Culture examination of organs revealed the highest percentage of mycobacteria in hamsters infected with the isolate D-C12 (75% positive hamsters) and the lowest percentage in hamsters infected with the isolate of RFLP type A-C10 (29.2%). Twenty-four months later, a change of RFLP type D-C12 to RFLP type D-C18 was recorded; that was likely caused by a transposition of one IS900 copy. After ip, sc, and po infections MAP was detected in the organs from 71.9%, 59.4%, and 37.5% hamsters, respectively. The culture on liquid Long medium did not increase sensitivity of culture examination.

Sponsorship

Partially supported by the MinAgr of the CR (grant No. 0002716201) and EC: No. QLK2-CT-2000-00928 and SSPE-CT-2004-501903 (supports the attendance to this Congress).