Abstract:
Introduction: Buruli ulcer disease is endemic in many developing countries in Africa. It is caused by Mycobacterium ulcerans, a toxin-producing bacterium with predilection for the skin and its deeper tissues. The exact mode of transmission is unclear and the pathogenesis is also not well un-derstood, necessitating further elucidation through animal studies.
Objective: The study assessed the infectivity of a Ghanaian Mycobacterium ulcerans isolate and the dose-response pattern in BALB/c mice.
Method: Ten standardized bacterial suspensions of different concentrations were prepared from the M. ulcerans isolate and inoculated into the foot-pads of the mice. Thereafter they were observed for clinical signs of Buruli ulcer, upon which they were serially euthanised and evaluated for patho-logical and microbiological changes.
Results: Irrespective of the inoculum dose, all the experimentally infected mice developed similar clinical lesions, from erythema to foot ulceration (3.1 to 6.7 weeks after inoculation). However, the higher the inoculum dose the earlier the onset of the lesions. After the development of foot ulcera-tion, mice that had received between 1 to 4 doses developed gangrene (5.7 to 7.2 weeks after inocu-lation) and died within a week, while those that had received 5 to 10 doses lost their limbs sponta-neously (5.6 to 6.1 weeks after inoculation), fol-lowed by sudden clinical recovery. Eight weeks after the spontaneous amputation the amputees relapsed with concomitant metastasis, anasarca and death. Acid-fast bacilli (AFBs) were detected in inoculated and non-inoculated limbs, tails, vis-ceral organs, faecal pellets and caecal contents of the mice. The AFBs detected in the caecal samples were innumerable and unusually long. Though AFBs were consistently detected in lymph nodes they were never detected in blood samples.
Conclusion: The findings suggest that the pro-gression and final outcome of an M. ulcerans in-fection maybe dose related. The unequivocal ab-sence of AFBs in the blood, but their consistent presence in lymph nodes located in the lower limbs right up to the neck, suggests that the mi-crobes are disseminated through the lymphatic system rather than through the blood.