PhD defence Lena Kraußer

Supervisors

• Prof Dr Bouke de Jong (ITM)

• Prof Dr Annelies Van Rie (University of Antwerp)

• Dr Sofie Braet (ITM)

Abstract

Although often regarded as a disease of the past, leprosy remains a public health concern in some parts of the world. This disease, caused by Mycobacterium leprae and Mycobacterium lepromatosis, affects the skin and nerves and, if diagnosed late, can lead to permanent disability and ongoing transmission. Although M. leprae was discovered over 150 years ago, major knowledge gaps still hinder effective control. This PhD thesis addresses several of these gaps using state-of-the-art molecular approaches.

For the first time, tongue dorsum samples from leprosy patients were systematically compared with skin biopsies and nasal swabs. While M. leprae DNA was detected by RLEP qPCR in tongue swabs and scrapes of patients with high bacillary loads, sensitivity was lower than for other sampling methods. Nevertheless, the confirmed presence of M. leprae on the tongue dorsum warrants further study, e.g. on transmission.

To support molecular studies in field conditions, RNA preservation was evaluated using M. tuberculosis as a culturable proxy. While RNAlater did not fully inactivate mycobacteria, a long-term stability experiment showed that 70% ethanol preserved RNA yield and integrity for up to 12 months at –20 °C, and quality was unaffected by multiple freeze–thaw cycles, suggesting a potential for field applicability.

Potential reasons for persistent leprosy hyperendemicity in the Comoros were further explored. Whole genome sequencing of a multiplex family from Anjouan identified candidate host susceptibility genes, including IL12RB1, HLA-A, RNH1, ATG3, and MALT1. In contrast, screening of ticks from all three Comorian islands revealed no M. leprae DNA, suggesting hat they likely do not play a role in transmission. Similarly, squirrels from leprosy-endemic Tshopo Province (DRC) tested negative for M. leprae and M. lepromatosis DNA, provisionally excluding them as reservoirs.