Histological findings associated with treatment response in cutaneous leishmaniasis: a clinicopathological correlation study.

BACKGROUND: Treatment responses to cutaneous leishmaniasis (CL) observed in Sri Lanka show variability, ranging from quick healing to delayed or failed responses to routine medication. The determinants of these differences in treatment response are not well defined. This study aimed to identify predictive features of treatment response and outcome in localized CL caused by Leishmania donovani, focusing on both clinical and histopathological findings in the patients. METHODS: Tissue sections (n = 103) derived from 3 mm punch biopsies of parasitologically confirmed patients were assessed. Patients were followed up weekly until complete healing of skin lesions and were reviewed at the end of 6 months and 1 year. RESULTS: Healing required 7-21 weekly doses of intralesional sodium stibogluconate (IL-SSG) (mean = 12.2 ± 0.622). Twenty-nine (28.1%) patients were identified as delayed responders. None had recurred at the end of 1 year. The demographic or clinical features (age, gender, lesion type, size, location, and lesion duration) did not significantly influence the treatment response. A heavy parasite load and acanthosis were significant predictors of a delayed response to treatment (P < 0.001). Higher parasite loads were associated with inflammation of the entire dermis (P = 0.008), more intense infiltration of macrophages (p = 0.001), and epidermal atrophy (P = 0.033). Well-formed granulomas were inversely proportional to parasite loads. CONCLUSIONS: Histology findings proved to be better prognostic markers than clinical features for delayed responders to treatment and will aid in targeted patient management when tissue biopsies are performed in the initial diagnosis of CL.

First evidence of experimental genetic hybridization between cutaneous and visceral strains of Leishmania donovani within its natural vector Phlebotomus argentipes.

Leishmaniasis is a neglected tropical disease caused by protozoan parasites of genus Leishmania, and transmitted by different species of Phlebotomine sand flies. More than 20 species of Leishmania are known to cause disease in humans and other animals. Leishmania donovani species complex is known to have a vast diversity of clinical manifestations in humans, but underlying mechanisms for such diversity are yet unknown. Long believed to be strictly asexual, Leishmania have been shown to undergo a cryptic sexual cycle inside its sandfly vector. Natural populations of hybrid parasites have been associated with the rise of atypical clinical outcomes in the Indian subcontinent (ISC). However, formal demonstration of genetic crossing in the major endemic sandfly species in the ISC remain unexplored. Here, we investigated the ability of two distinct variants of L. donovani associated with strikingly different forms of the disease to undergo genetic exchange inside its natural vector, Phlebotomus argentipes. Clinical isolates of L. donovani either from a Sri Lankan cutaneous leishmaniasis (CL) patient or an Indian visceral leishmaniasis (VL) patient were genetically engineered to express different fluorescent proteins and drug-resistance markers and subsequently used as parental strains in experimental sandfly co-infection. After 8 days of infection, sand flies were dissected and midgut promastigotes were transferred into double drug-selective media. Two double drug-resistant, dual fluorescent hybrid cell lines were recovered, which after cloning and whole genome sequencing, were shown to be full genomic hybrids. This study provides the first evidence of L. donovani hybridization within its natural vector Ph. argentipes.