Understanding differences in clinical presentations of cutaneous leishmaniasis in an endemic disease focus

Leishmaniasis is one of the most important neglected tropical diseases: a group of diseases united by the fact that they impact the poorest communities and attract little political interest and less funding for control or basic research than other diseases. Transmitted by sandflies, leishmaniasis is a parasitic disease that affects an estimated 12 million people in 98 countries, causing disfiguring infections of the skin and other tissues, and tens of thousands of deaths. A striking feature of leishmaniasis is that diverse forms of the disease are caused by a single group of parasites. Visceral leishmaniasis (VL) occurs where parasites migrate and multiply in organs such as the liver and spleen. VL is usually fatal if not treated, as patients become immunocompromised and highly susceptible to other diseases. Cutaneous leishmaniasis (CL) is restricted to the skin and superficial tissues and can present in three different forms: localised CL (LCL) causes damage, such as small ulcers, only at the site of the insect bite; while other infections can be more widespread (diffuse CL; DCL) or when parasites invade and destroy mucosal tissue of the nose, lips or palate, leading to severe disfigurement (mucosal CL; MCL). There is a great variety in the severity of CL, with some infections healing spontaneously (usually LCL), while others persist and form large wounds. Healed lesions invariably result in scarring, which in some societies leads to severe social stigma and so has a profound impact on the lives of patients. These different forms of disease (known as clinical presentations) are associated with different species but there is substantial variation within species and it is poorly understood why Leishmania parasites cause different forms of disease.

We propose to study CL in Ethiopia, where the disease is an important health problem. We will work in an area of North West Ethiopia, where Leishmania aethiopica is causing an increasing incidence of localised CL, diffuse CL and mucosal CL. Since the diseases occur in the same region and in the same human and vector populations, this focus is a unique place to unravel the biological basis of the different clinical presentation of CL. We will generate whole-genome data for parasites from each of the different presentations, and also quantify genome-wide host gene expression and the immune response to Leishmania infection in both the lesions and blood of patients with each form of CL. In this way we will identify the genes and types of immunity involved in particular types of CL. We have developed a non-invasive, painless way to sample CL-affected skin that allows us to take samples in the hard-to-reach communities most affected by the disease. The data from the clinical database will be used to explore if any clinical and epidemiological factors associated with the different presentations of CL in our cohort, but will also be included in the statistical analysis of the parasite and host data to identify and unravel associations with the different presentations.

This study will elucidate the pathogenesis of CL, which is essential for the development of new strategies to prevent and treat leishmaniasis - both vaccines and better diagnostic tests. The project will also enhance capacity for biomedical research in Ethiopia and establish a framework for future research in this setting.

The incidence of cutaneous leishmaniasis (CL), a neglected vector-borne tropical disease, is increasing with around 1 million new cases every year. We propose to study differences in clinical presentations of CL in an endemic disease focus: infections with Leishmania aethiopica in North West Ethiopia represents a unique opportunity to unravel the biological basis of the differences in clinical phenotypes, as closely related parasites in a single focus can cause three different cutaneous diseases: localised CL (LCL), characterised by single or multiple localised lesions on exposed skin; mucosal CL (MCL), affecting the mucosa of the nose, mouth or pharynx; and diffuse CL (DCL), characterised by numerous non-ulcerating nodules.
To elucidate the pathogenesis of this multifactorial disease, we will recruit and follow the clinical history of patients with L. aethiopica infections, including 80 of each presentation. Each case will be reviewed by the clinical team on site. The scientific team will obtain the data for analysis after de-identification of the patients by creating unique patient IDs. The downstream analysis will be performed using the patient IDs. We will isolate parasites from all patients and generate whole-genome data for all isolates to identify parasite genotypes associated with particular manifestations. Detailed phenotyping will use standard cytokine assays and transcriptomics of skin tape strips, lesion biopsies and blood samples. Analysis of these will seek to identify distinct immunological and gene expression signatures of each presentation.

The ultimate goal of the proposed research is to enable us to generate novel mechanistic hypotheses about the immunopathology of CL that will be amenable to further test in future work. While this research is basic biomedical science, our planned investigation will have a number of different types of impact.

Our scientific results will have direct and immediate impacts. Given the relative lack of clinical cohorts with in-depth immunological characterisation, our results will be of wide interest to basic scientists interested in parasitology and immunology. In particular, researchers working on other Leishmania species will be interested in testing the generality of our findings. Of particular importance, persistence of parasites in visceral organs is key to the pathology of fatal visceral leishmaniasis, so our findings on the basic mechanisms of L. aethiopica persistence in its cutaneous niche will be of interest beyond cutaneous leishmaniasis. The importance of Leishmania spp. as a model of the immune response to intracellular parasites means our results will have impact for a wider constituency of basic immunologists. There are few large-scale population genomic datasets for eukaryotic pathogens, so our results and the underlying genomic data will have impact in a wider field of researchers interested in population genetics of parasites.

In the longer term, our results will also impact more applied scientists and clinicians in both industry and academia interested in Leishmania control. The host signatures we identify should feed into the development of new targeted immunotherapies and diagnostics that can be implemented in low- and middle-income countries. For example, diagnostic tests that could predict the likely course of a L. aethiopica infection would allow early treatment targeted at patients likely to develop severe or persistent disease and so could have immediate impact on patient care. Following further work, there could be longer-term impacts on the treatment of leishmaniasis. There is significant interest in developing and testing possible approaches to vaccinate against CL. Better understanding of host and parasite pathways involved in leishmaniasis pathology might also reveal novel targets for novel drugs against these diseases. These would be particularly welcome as existing drugs are either highly toxic or prohibitively expensive for many endemic regions and resistance to many anti-leishmania compounds is an increasing problem.

In order to undertake this project successfully and perform competitively in different areas of research, we have brought together a team of specialists in parasite genomics, immunology, bioinformatics and treatment of CL. This work will also impact on the careers of the staff and students involved in the project by further training and acquisition of new skills. They will be working in close association with the applicants and collaborators and will present their work in lab meetings and group discussions. The applicants will also interact with and train other students and visitors working on related projects in the laboratories involved. These impacts will be particularly important in Gondar, where this project should give a significant boost to the research base and contribute greatly to developing capacity for future research.

We will also use the results of our research for public engagement events that will benefit the wider public by increasing awareness of leishmaniasis and neglected tropical diseases in general.