Genetic diversity of Leishmania tropica: Unexpectedly complex distribution pattern

Upregulation of antioxidant genes in antimony-resistant Leishmania tropica clinical isolates

BACKGROUND

Increasing resistance to antimonial drugs has become a significant challenge in effective treatment in endemic regions of leishmaniasis. Antioxidant defense plays a crucial role in antimony resistance by combating antimonial-induced oxidative stress. Accordingly, we investigated the transcript levels of some antioxidant genes in antimony-sensitive and resistant clinical Leishmania tropica isolates.

METHODS

In the current study, 22 Leishmania tropica isolates from ACL patients who presented responsive or unresponsive to antimony were examined. The susceptibility of parasites against SbV and hydrogen peroxide (H2O2) was analyzed. We evaluated the transcript levels of five genes, including cytosolic and mitochondrial tryparedoxin (cTXN, mTXN), cytosolic and mitochondrial tryparedoxin peroxidase (cTXNPx, mTXNPx), and ascorbate peroxidase (APX) in antimony-sensitive and resistant L. tropica clinical isolates.

RESULTS

The in-vitro susceptibility to SbV in intracellular amastigotes revealed 3.82 times higher IC50 in resistant isolates compared to sensitive ones. The IC50 toward H2O2 in resistant isolates was 1.6 times higher than in sensitive ones, positively correlated with SbV IC50 values. The average transcript expression level of cTXNPx, mTXNPx, cTXN, and APX genes significantly increased in resistant isolates by 2.51, 1.69, 2.41, and 2.12-fold compared to sensitive ones. The highest correlation coefficient between the gene expression and SbV IC50 values belonged to the cTXNPx, cTXN, APX, mTXN, and mTXNPx genes, respectively. The average transcript expression level of cytosolic TXN and TXNPx in resistant L. tropica isolates was higher than its mitochondrial counterpart.

CONCLUSIONS

The data presented here revealed a phenotypic heterogeneity in antioxidant gene expression among L. tropica clinical isolates. Overall, the upregulation of genes involved in antioxidant defense could probably contribute to natural antimony resistance in L. tropica clinical isolates.

Unexpectedly complex distribution pattern of chestnut pest Niphades castanea Chao (Coleoptera: Curculionidae) based on mtDNA and ITS markers

Niphades castanea Chao (Coleoptera: Curculionidae), an important fruit insect pest of chestnuts (Castanea spp.), could cause chestnut involucre abscission ahead of time through larvae boring and feeding basal involucres, eventually causing huge economic losses. In this research, mitochondrial (COI and COII) and nuclear (ITS1) markers were used to investigate genetic variation among 15 different geographical populations of chestnut pest N castanea. The molecular diversity of N. castanea populations revealing three main phylogenetic clusters, with cluster I specifically distributed at high elevations in the western sampling points. Mitochondrial genes indicated population expansion events, and the ITS1 marker suggested a history of population expansion. Genetic diversity differentiation was significant among populations, indicating that geographical isolation impacts genetic differentiation among these places. AMOVA analyses confirmed substantial genetic differentiation between populations. Mantel correlogram analyses revealed a significant positive correlation between genetic differentiation and altitude/geographical distance at lower elevations and ranges, which reversed to a negative correlation at higher altitudes and ranges for all markers, indicating the role of altitude and geographical distance in shaping genetic diversity in N. castanea. This study contributes to a comprehensive understanding of the distribution, genetic diversity, and evolutionary history of N. castanea in the central of China, underscoring the impact of geographical factors on its genetic structure.

Novel duplex TaqMan-based quantitative PCR for rapid and accurate diagnosis of Leishmania (Mundinia) martiniquensis and Leishmania (Mundinia) orientalis, responsible for autochthonous leishmaniasis in Thailand

The World Health Organization has recently declared Thailand a leishmaniasis hotspot in Southeast Asia due to the continuous increase in new symptomatic and asymptomatic cases over the years. This emerging parasitic disease is known to be caused by two autochthonous species of Leishmania belonging to the newly described subgenus Mundinia, namely L. martiniquensis and L. orientalis. In Thailand, clinical cases due to L. martiniquensis typically present with visceral leishmaniasis, whereas L. orientalis mainly causes localized cutaneous leishmaniasis. Although Leishmania species confirmation is essential for clinical diagnosis and treatment planning, the availability of highly accurate and rapid diagnostic methods remains limited. In this study, we developed a duplex TaqMan quantitative PCR assay using newly designed species-specific primers and probes based on sequences from the nucleotide and genome databases of Leishmania spp. retrieved from GenBank. The duplex qPCR assay was optimized to specifically amplify the internal transcribed spacer 1 (ITS1) of L. martiniquensis and the heat shock protein 70 (type I) intergenic region (HSP70-I IR) of L. orientalis with high amplification efficiencies. The performance of the optimized duplex qPCR was evaluated by analyzing 46 DNA samples obtained from cultures, and clinical and insect specimens, consistent with the results of the previously validated 18S rRNA-qPCR and ITS1-PCR. The duplex qPCR could detect both species of Leishmania at a limit of detection of one copy per reaction and did not cross-amplify with other pathogen DNA samples. Standard curves of the singleplex and duplex assays showed good linearity with excellent amplification efficiency. Using conventional ITS1-PCR and plasmid sequencing as a reference standard assay, the duplex qPCR showed diagnostic sensitivity and specificity of 100% and positive and negative predictive values of 100% for both Leishmania species with a perfect level of agreement (kappa = 1.0). The novel duplex TaqMan-based qPCR has shown to be a rapid, cost-effective, and highly accurate diagnostic tool for the simultaneous detection and identification of two autochthonous Leishmania spp. in a variety of clinical and entomological samples. This will greatly facilitate early diagnosis, treatment monitoring, and surveillance, especially in leishmaniasis-endemic areas where sequencing-based diagnosis is not routinely available.

Insights into the trypanothione system in antimony-resistant and sensitive Leishmania tropica clinical isolates

Pentavalent antimonials are the mainstay treatment against different clinical forms of leishmaniasis. The emergence of resistant isolates in endemic areas has led to treatment failure. Unraveling the underlying resistance mechanism would assist in improving the treatment strategies against resistant isolates. This study aimed to investigate the RNA expression level of glutathione synthetase (GS), Spermidine synthetase (SpS), trypanothione synthetase (TryS) genes involved in trypanothione synthesis, and thiol-dependent reductase (TDR) implicated in drug reduction, in antimony-sensitive and -resistant Leishmania tropica isolates. We investigated 11 antimony-resistant and 11 antimony-sensitive L. tropica clinical isolates from ACL patients. Drug sensitivity of amastigotes was determined in mouse macrophage cell line J774A.1. The RNA expression level in the promastigote forms was analyzed by quantitative real-time PCR. The results revealed a significant increase in the average expression of GS, SpS, and TrpS genes by 2.19, 1.56, and 2.33-fold in resistant isolates compared to sensitive ones. The average expression of TDR was 1.24-fold higher in resistant isolates, which was insignificant. The highest correlation coefficient between inhibitory concentration (IC50) values and gene expression belonged to the TryS, GS, SpS, and TDR genes. Moreover, the intracellular thiol content was increased 2.17-fold in resistant isolates compared to sensitive ones and positively correlated with IC50 values. Our findings suggest that overexpression of trypanothione biosynthesis genes and increased thiol content might play a key role in the antimony resistance of L. tropica clinical isolates. In addition, the diversity of gene expression in the trypanothione system and thiol content among L. tropica clinical isolates highlighted the phenotypic heterogeneity of antimony resistance among the parasite population.

Nanopore-Based Surveillance of Leishmania Parasites in Culicoides Latrielle (Diptera: Ceratopogonidae) Caught from the Affected Community and Tham Phra Cave in Chiang Rai Province, the Endemic Area of Leishmaniasis in Northern Thailand

In this research, we elucidated the species composition of Culicoides biting midges, infection prevalence, and genetic diversity of Leishmania parasites circulating in the affected community in Chiang Rai Province, being the most endemic area in Northern Thailand. A total of 146 parous and gravid females, belonging to at least twelve Culicoides species in five subgenera and one species group, were trapped from three collection sites with an overall Leishmania prevalence of 26.7% (39/146). Leishmania was detected, using ITS1-PCR, in C. mahasarakamense (15), C. guttifer (11), C. (Trithecoides) spp. (8), C. jacobsoni (2), C. oxystoma (2), and C. orientalis (1). The evidence of Leishmania infection in these last five species represents new records in Northern Thailand. Given a high infection rate in cavernicolous specimens, this indicates an increased risk of parasite exposure when visiting the cave. Using the nanopore amplicon sequencing, L. martiniquensis was ubiquitously identified in all positives, and more than half of these were also co-infected with L. orientalis. The genetic diversity analysis revealed 13 and 17 unique haplotypes for L. martiniquensis and L. orientalis, respectively. Higher haplotype diversity and relatively low nucleotide diversity were observed in both parasite populations, suggesting recent population divergence. Neutrality tests (Tajima's D and Fu and Li's D) showed to be significantly negative, indicating rapid population growth or a selective sweep. Moreover, dominant haplotypes of both Leishmania species were 100% identical to those in all leishmaniasis patients previously reported from Northern Thailand, strongly supporting the imperative role of Culicoides spp. in disease transmission. Essentially, this research provides the first entomological surveillance data representing the sympatric existence, transmission dynamics, and genetic complexity of two autochthonous Leishmania (Mundinia) parasites in several Culicoides species in the endemic area of Northern Thailand. This would contribute to a more complete understanding of the epidemiology of vector infection and facilitate the development of vector control programs to effectively reduce the transmission of this neglected tropical disease in endemic areas of Northern Thailand.

Genetic variation and geographic distribution of Leishmania orientalis and Leishmania martiniquensis among Leishmania/HIV co-infection in Thailand

Since 1999, the number of asymptomatic leishmaniasis cases has increased continuously in Thailand, particularly among patients with HIV who are prone to develop symptoms of cutaneous and visceral leishmaniasis further. The asymptomatic infection could play a key role in Leishmania transmission and distribution. Understanding population structure and phylogeographic patterns could be crucially needed to develop effective diagnoses and appropriate guidelines for therapy. In this study, genetic variation and geographic distribution of the Leishmania/HIV co-infected population were investigated in endemic northern and southern Thailand. Interestingly, Leishmania orientalis was common and predominant in these two regions with common regional haplotype distribution but not for the others. Recent population expansion was estimated, probably due to the movement and migration of asymptomatic individuals; therefore, the transmission and prevalence of Leishmania infection could be underestimated. These findings of imbalanced population structure and phylogeographic distribution patterns provide valuable, insightful population structure and geographic distribution of Leishmania/HIV co-infection to empower prevention and control of transmission and expansion of asymptomatic leishmaniasis.

Revisiting epidemiology of leishmaniasis in central Asia: lessons learnt

In this work we reviewed historical and recent data on Leishmania spp. infection combining data collected in Turkmenistan, Uzbekistan, Kazakhstan, Kyrgyzstan, Iran, China and Mongolia. We specifically focused on a complex of co-existing species (Leishmania major, Leishmania turanica and Leishmania gerbilli) sharing the same animal reservoirs and vectors. In addition, we analysed the presence of dsRNA viruses in these species and discussed future research directions to identify species-specific traits, which may determine susceptibility of different Leishmania spp. to viral infection.

Low genetic heterogeneity of Leishmania major in different geographical regions of Iran

To examine the genetic diversity of Leishmania major, 100 Giemsa-stained positive slides were collected from endemic foci of Iran (Northeast, Central, and Southwest provinces) over two consecutive years during 2019-2021. The Leishmania ITS-rDNA gene was amplified and Leishmania sp. was recognized by PCR-RFLP and sequencing. In addition, 178 registered ITS-rDNA sequences from other geographical regions of Iran were retrieved from GenBank, including different host species (human, sandfly and rodent). A total of 40 new haplotypes were discovered using the ITS-rDNA sequence analysis. IR29 (20.6%) and IR34 (61%) were the two most common haplotypes, represented by a star-like feature in the overall population. Analysis of the molecular variance test revealed low genetic diversity of L. major in human cases (Haplotype diversity; 0.341), rodent (Hd; 0.387) and sandfly (Hd; 0.390) sequences. The lowest genetic diversity of L. major was observed in Southwest/Southeast Iran (Hd: 0.104-0.286). The statistically Fst value indicated that L. major is not genetically differentiated between geographic regions of Iran, except for the Northeast-Southwest (Fst: 0.29055) and Central-Southwest (Fst: 0.30294) population pairs. The current study as the first investigation discloses new perspectives for further evaluation in the identification local transmission paradigms and initiating effective prevention strategies.

The efficacy of AuNP-probe conjugate nanobiosensor in non-amplification and amplification forms for the diagnosis of leishmaniasis

Nanobiosensor platforms have emerged as convenient and promising approaches with remarkable efficacy for the diagnosis of infectious diseases. Gold nanoparticles (AuNPs) have been widely used due to numerous advantageous properties such as optical, electrical, physicochemical and great biomolecules binding capabilities. This study aimed to apply AuNP-Probe Conjugate for the detection of Leishmania spp., using colorimetric and amplification methods targeting parasitic ITS2 fragment. The first method was carried out by hybridization of 10µL of DNA with 4 µL of probe and addition of 5 µL of 0.2 N HCl (non-amplification method). Second method was followed by polymerase chain reaction (PCR) amplification using thiolated primer, 5 µL of AuNP and 5 µL of 0.2 N HCl. The appearance of red and purple colors indicated positive and negative results, respectively. The minimum of detection for non-amplification and amplification methods for three strains of Leishmania namely L. major, L. tropica and L. infantum were determined to be 32 fg/µL and 16 fg/µL, respectively. Sensitivity for detection of visceral leishmaniasis (VL) for non-amplification and amplification methods included 96% and 100%, respectively and for cutaneous leishmaniasis (CL) included 98% and 100%, respectively. The results of this investigation revealed that sensitivity of amplification method was the same as RT-qPCR, while that of non-amplification method was lower. However, this method was promising because of no need for any equipment, high specificity, enough sensitivity, low cost and rapidity (less than 30 min) to complete after genomic DNA extraction.

Environmental, Climatic, and Parasite Molecular Factors Impacting the Incidence of Cutaneous Leishmaniasis Due to Leishmania tropica in Three Moroccan Foci

Cutaneous leishmaniasis (CL) occurring due to Leishmania tropica is a public health problem in Morocco. The distribution and incidence of this form of leishmaniasis have increased in an unusual way in the last decade, and the control measures put in place are struggling to slow down the epidemic. This study was designed to assess the impact of climatic and environmental factors on CL in L. tropica foci. The data collected included CL incidence and climatic and environmental factors across three Moroccan foci (Foum Jemaa, Imintanout, and Ouazzane) from 2000 to 2019. Statistical analyses were performed using the linear regression model. An association was found between the occurrence of CL in Imintanout and temperature and humidity (r² = 0.6076, df = (1.18), p-value = 3.09 × 10⁻⁵; r² = 0.6306, df = (1.18), p-value = 1.77 × 10⁻⁵). As a second objective of our study, we investigated the population structure of L.tropica in these three foci, using the nuclear marker internal transcribed spacer 1 (ITS1). Our results showed a low-to-medium level of geographic differentiation among the L.tropica populations using pairwise differentiation. Molecular diversity indices showed a high genetic diversity in Foum Jemaa and Imintanout; indeed, 29 polymorphic sites were identified, leading to the definition of 13 haplotypes. Tajima’s D and Fu’s F test statistics in all populations were not statistically significant, and consistent with a population at drift–mutation equilibrium. Further analysis, including additional DNA markers and a larger sample size, could provide a more complete perspective of L. tropica’s population structure in these three regions. In addition, further research is needed to better understand the impact of climatic conditions on the transmission cycle of Leishmania, allowing both for the development of effective control measures, and for the development of a predictive model for this parasitosis.

Experimental Hybridization in Leishmania: Tools for the Study of Genetic Exchange

Despite major advances over the last decade in our understanding of Leishmania reproductive strategies, the sexual cycle in Leishmania has defied direct observation and remains poorly investigated due to experimental constraints. Here, we summarize the findings and conclusions drawn from genetic analysis of experimental hybrids generated in sand flies and highlight the recent advances in generating hybrids in vitro. The ability to hybridize between culture forms of different species and strains of Leishmania should invite more intensive investigation of the mechanisms underlying genetic exchange and provide a rich source of recombinant parasites for future genetic analyses.

The Natural Compound Hydrophobic Usnic Acid and Hydrophilic Potassium Usnate Derivative: Applications and Comparisons

Usnic acid is the best-studied lichen metabolite, presenting several biological activities, such as antibacterial, immunostimulating, antiviral, antifungal, anti-inflammatory, and antiparasitic agents; despite these relevant properties, it is a hydrophobic and toxic molecule. In this context, scientific research has driven the development of innovative alternatives, considering usnic acid as a source of raw material in obtaining new molecules, allowing structural modifications (syntheses) from it. The purpose is to optimize biological activities and toxicity, with less concentration and/or response time. This work presents a literature review with an analogy of the hydrophobic molecule of usnic acid with its hydrophilic derivative of potassium usnate, emphasizing the elucidation and structural characteristics, biological activities, and toxicological aspects of both molecules, and the advantages of using the promising derivative hydrophilic in different in vitro and in vivo assays when compared to usnic acid.