Transmission dynamics, distribution and diagnostics of cutaneous leishmaniasis in southwestern Ethiopia

Subtitle:a basis for disease management

Cutaneous leishmaniasis (CL) is a neglected tropical disease characterized by nodular and crusty skin lesions, mainly on people’s face and extremities, resulting in disfiguring scars after healing. It is caused by Leishmania parasites, which are transmitted by female phlebotomine sand flies during blood feeding. The disease is a major public health problem in Ethiopia, where Leishmania aethiopica affects approximately 20,000 to 50,000 people annually and transmission is zoonotic, with hyraxes serving as reservoir hosts. The first main objective of this thesis was to thoroughly explore the transmission cycle of CL in an endemic hotspot in southwestern Ethiopia and map the distribution of the vector and the infection in a larger surrounding area. We found that aside from hyraxes, humans also play an important role in transmission, hence early diagnosis and treatment of the human reservoir is pivotal for disease management. Furthermore, we show that the vector is mainly biting at night indoors. This information can be used to limit the human-vector contact by for instance the use of bed nets. The distribution of both the vector and the disease is much more widespread than reported, which is calling for better surveillance. The generated distribution map can be used for guidance of control interventions. The second objective was to comparatively assess the performance of different molecular assays for detection of Leishmania aethiopica in clinical samples and sand flies. We show that the probe-based LC kDNA PCR, which was developed for L. aethiopica detection specifically, performs superior and should be implemented in routine practice for CL diagnosis in case microscopy results are negative. For large entomological or eco-epidemiological studies, however, we recommend the use of a crude high-salt extraction buffer with ethanol precipitation step for DNA isolation in combination with a SYBR Green qPCR assay targeting the spliced leader (SL-)RNA sequence. For the third objective, we assessed that the recently introduced matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) protein profiling technique is a suitable alternative for unambiguous sand fly species determination in Ethiopia. Collectively, this thesis lays groundwork for adequate CL detection and disease control and indicates the use of novel techniques for accurate, cost-effective future entomological surveys in Ethiopia.

Publication year:2020

Keywords:Doctoral thesis

Accessibility:Open