Approaches to improve treatment and early diagnosis of Buruli ulcer. the role of local and systemic immune responses

Buruli ulcer (BU) hits thousands of individuals every year in over 30 countries worldwide, primarily children in remote areas of sub-Saharan Africa. This devastating necrotizing skin infection is caused by Mycobacterium ulcerans, a cytotoxic macrolide producing environmental pathogen. The disease distorts and cripples those affected and has great socio-economic impact on people living in endemic regions. Currently recommended treatment options are surgical excision of the lesion, systemic administration of as rifampicin and streptomycin (R-S) or a combination of both. Clinical diagnosis of BU lesions requires the expertise of a skilled physician or health worker, and proper medical care is expensive, time-consuming or not available at all in many BU endemic regions of Africa. Thus, rapid diagnostic tools as well as improved established or new alternative therapies which are safe, inexpensive and easy to handle in a rural setting are urgently needed and the present work focused on these important issues.
Histopathological hallmark of progressing BU disease is a poor inflammatory response despite clusters of extracellular bacilli inside necrotic subcutaneous areas. We conducted detailed histopathological studies on the efficacy of chemotherapy with R-S to restore the local immune responses in early (nodule and plaque) and late (ulcerative) BU lesions, respectively. In early lesions AFB internalized by macrophages and neutrophils were already found after two to four weeks of treatment and started to display irregular ZN staining after eight weeks. Final clearance of the bacterial load depended on the initial size of clusters and the surrounding necrosis. After eight weeks of R-S therapy ulcerative lesions comprised only mycobacterial debris inside focally distributed mononuclear phagocytes. Local cellular immune responses were re-activated very quickly (after two weeks acute infiltration was already prominent) and developed further during the course of antibiotic therapy, resulting in the formation of ectopic tertiary lymphoid tissue. Granulomas and other lymphoid structures developed both in early and late stage lesions in the course of antibiotic treatment, but only nodules and plaques showed abscessus formation, severe haemorrhages and extensive necrosis after completion of eight to twelve weeks chemotherapy. Administration of R-S is efficacious to cure BU, but immunopathological adverse events due to a chronic overreaction of the immune system may cause healing retardation. Thus, treatment strategies have to be further improved. Our results demonstrate that histopathology can serve as a valuable tool for efficacy evaluation.
M. ulcerans grows best at temperatures around 30°C and not above 37 °C and this property makes the application of heat a treatment option. We employed the phase change material sodiumacetatetrihydrate which is widely used in commercial pocket heat pads as a heat application system for thermotherapy. Laboratory reconfirmed patients with ulcerative BU lesions were included in a proof of principle study and treated for four to six weeks. Patients with large defects had skin grafting after successful heat treatment while smaller ulcers healed completely without further intervention. Punch biopsies were analysed for histopathological changes and local immunological reactions during heat therapy. While massive cellular infiltration was observed during antibiotic therapy, the extent of total leukocyte infiltration in the lesion did not increase during thermotherapy. This may favour a rapid transition from inflammation to healing, as indicated by the clinical response to heat treatment, which was characterized by an extraordinarily rapid epithelization and healing process. All patients remained relapse-free within twelve months of follow-up suggesting thermotherapy a future treatment option for BU.