Cutaneous leishmaniasis : treatment and genetic mechanisms affecting outcome

Abstract

Leishmaniasis is a neglected parasitic disease and a rare diagnosis in non-endemic countries in Europe. Migration, geopolitical conflicts and climate change have increased awareness of this infection in Europe, as more patients with leishmaniasis are admitted to health care.

Pentavalent antimonial has been used for decades as the first-line treatment regardless of clinical manifestations and Leishmania species. Treatment failures and relapses, possibly due to drug resistance, in combination with drug toxicity, have created the need for new treatment regimens. Today, several alternatives are available and recommended depending on the clinical manifestation, Leishmania spp. and geographic region.

The objectives of this thesis were to: Investigate the genome of Leishmania tropica, focusing on genetic diversity and correlate it with previous antimonial exposure; Study treatment and outcome of leishmaniasis in non-endemic countries in Europe

In the first two studies, Study I and Study II, we investigated the genome of 22 L. tropica isolates and described genetic diversity and genetic mechanisms for adaptation to environmental changes and drug pressure.

Among the isolates, we observed extensive genetic variation with high heterozygosity and aneuploidy, and evidence of genetic exchange within and among isolates. The latter indicates hybridisation and a possible presence of sexual or parasexual mechanisms. It may be postulated that the high genetic diversity and recombination explain the challenges seen when treating cutaneous leishmaniasis caused by L. tropica.

L. tropica has several genetic mechanisms to adapt to environmental changes. We observed a higher non-synonymous single nucleotide polymorphism rate in the isolates from Syria at the H locus, compared with in isolates from Afghanistan and Iran. This locus has several mechanisms connected to drug resistance in other Leishmania spp. No increased copy number variation was observed in genes correlated with drug resistance. Instead, among isolates previously exposed to antimonial multiple genes involved in essential cellular functions were amplified, indicating several genetic mechanisms involved in surviving drug pressure.

In Studies III and IV, we evaluated the treatments and outcome in non-endemic countries in Europe. All patients with leishmaniasis in Sweden between 1996-2016 were included in Study III. The number of cases increased during 2013-2016 in Sweden, mainly due to increased migration from endemic areas. L. tropica was the most common species among patients with cutaneous leishmaniasis in the Swedish cohort. Treatment was started within the first month after suspicion of leishmaniasis in 66% of the patients and the overall cure rate was 70%, suggesting a high awareness within the health care system in Sweden.

In the European study, cutaneous leishmaniasis patients with L. major or L. tropica were evaluated with regard to treatment and outcome. Patients infected with L. major were mainly infected in North Africa, when visiting family and friends and patients with L. tropica were mainly migrants from Syria. Treatment with pentavalent antimony had a cure rate in line with those of previous studies, as did treatment with liposomal amphotericin B and cryotherapy. All patients with L. major were cured within the year after diagnosis compared with L. tropica where 21 % patients relapsed within the first year.

This thesis has aimed to enhance the knowledge and understanding of cutaneous leishmaniasis. By analysing the complex L. tropica genome, we tried to better understand intra- and inter-chromosomal changes in diversity driven by recombination and aneuploidy and correlate the single nucleotide polymorphism and copy number variation to previous antimony exposure. Evaluating treatments, new drugs and treatment regimens, and outcome in non-endemic countries provides important information for future guidelines. By combining the two perspectives in the leishmaniasis research field, we hoped to enhance the understanding of the complex genetic mechanisms used by Leishmania to survive antimonial treatment.