Cutaneous leishmaniasis caused by Leishmania infantum transmitted by Phlebotomus tobbi

A real-time ITS1-PCR based method in the diagnosis and species identification of Leishmania parasite from human and dog clinical samples in Turkey

Human visceral leishmaniasis (VL) caused by L. infantum and cutaneous leishmaniasis (CL) caused by L. tropica and L. infantum have been reported in Turkey. L. infantum is also responsible for canine leishmaniasis (CanL) and it is widely common in the country. The main aim of the present study was to design a real-time PCR method based on the internal transcribed spacer 1 (ITS1) region in the diagnosis of all clinical forms of leishmaniasis in Mediterranean, and to identify the species directly from clinical samples. Totally, 315 clinical specimens, human/canine visceral (blood, bone marrow, lymph node) and cutaneous (lesion aspiration) samples, and 51 Turkish Leishmania isolates typed by isoenzymatic method were included in the study. For optimization, DNA samples of the 34 strains were amplified by conventional ITS1-PCR and then sequenced for designing the primers and probes, allowing the species identification. Following the validation with the isolates, the test was applied on clinical samples and melting temperatures were used for genotyping. A group of PCR products were further sequenced for confirmation and assigning the inter- and intraspecies heterogeneity. The diagnosis of leishmaniasis is successfully achieved by the new real-time PCR method, and the test identified 80.43% of human and canine VL samples as L.infantum and 6.52% as L.tropica; 52.46% of CL samples as L. infantum and 26.90% as L. tropica. In 13.04% of visceral and 20.62% of cutaneous samples, two peaks were observed. Hovewer, the higher peak was found to be concordant with the sequencing results in 96.96%, in terms of species identification. The real-time ITS1 PCR assay clearly identified the leishmanial species in 81.58% of all clinical samples. Genotypic variations of Leishmania parasites in Turkey within species and intraspecies were observed, and L. tropica is also found as causative agent of human and canine VL in Turkey.

Leishmaniasis caused by Leishmania parasites are seen as cutaneous (CL) and visceral (VL) clinical forms in Turkey. Leishmania (L.) tropica and L. infantum were determined as CL agents, while L. infantum was incriminated for VL in the country. Canine leishmaniasis (CanL) is widely common throughout the country and L. infantum is the responsible agent of the disease. Related to Leishmania species diversity and different clinical forms in human and dogs in this geographical area, the identification of the parasite species prefers to be done during the time of diagnosis. Internal transcribed spacer region was chosen as the target area for developing a real-time PCR assay to use as a fast and standardized diagnostic method and species identification simultaneously. Clinical samples from parasitologically/serologically proven cases and isolates were included the study, and high positivity rate in species identification was obtained. The method can also determine the intragenomic heterogeneity in Leishmania tropica and L. infantum. The assay presents a sufficient sensitivity for fast and correct detection of leishmaniasis directly from clinical materials. L. tropica and L. infantum were found as causative agents of human CL, VL and CanL in Turkey. Knowledge about differences in the parasites is useful for future studies in Turkey.

Seasonal variation in the prevalence of sand flies infected with Leishmania donovani

BACKGROUND

Visceral Leishmaniasis (VL) is a life threatening neglected infectious disease in the Indian subcontinent, transmitted by the bite of female sand flies. Estimation of the infectivity in the vector population, collected in different seasons, may be useful to better understanding the transmission dynamics of VL as well as to plan vector control measures.

METHODOLOGY

We collected sand flies from highly endemic regions of Bihar state, India for one year over three seasons. The species of the sand flies were confirmed by species-specific PCR-RFLP. Leishmania donovani infection was investigated in 1397 female Phlebotomus argentipes using PCR, targeting the Leishmania specific minicircle of the kDNA region. Further, the parasitic load in the infected sand flies was measured using quantitative PCR.

CONCLUSION

Though sand flies were most abundant in the rainy season, the highest rate of infection was detected in the winter season with 2.84% sand flies infected followed by the summer and rainy seasons respectively. This study can help in vector elimination programmes and to reduce disease transmission.

Entomological and ecological studies in a new potential zoonotic leishmaniasis focus in Torres Novas municipality, Central Region, Portugal

In Portugal human and canine leishmaniasis are caused by Leishmania infantum, and Phlebotomus perniciosus and P. ariasi are the proven vectors. Three main foci were identified in eighty's decade: Trás-os-Montes and Alto Douro region, Lisbon region and Algarve region, but according to OnLeish observatory data, canine leishmaniasis cases have been reported from several other regions, for which sand fly species and their infection rates are unknown. This study is the first phlebotomine survey in Torres Novas municipality, Santarém District, Portugal. The main objectives were to identify the phlebotomine species, their bioecological aspects, Leishmania infection rate and the risk factors for the presence of phlebotomine species in the municipality. From June to November, 2010, 275 biotopes were surveyed with CDC light-traps. Captures covered the 17 parishes of the municipality and included domestic, peridomestic and sylvatic biotopes. Specimens were identified morphologically and females were used for molecular detection of Leishmania and bloodmeal identification. Simple and multiple logistic regression analysis were used to identify risk factors for phlebotomine presence. Nonparametric tests were used to compare densities of independent groups. A total of 1262 sand flies were captured and identified, and four species detected: P. perniciosus (73.69%), P. ariasi (8.16%), P. sergenti (6.58%) and Sergentomyia minuta (11.57%). In 71.4% localities at least one L. infantum proven vector species was present. Risk factors were identified as: high average temperatures and low relative humidities, sheltered locations and absence of strong wind, presence of pine trees as dominant vegetation, peridomestic biotopes, particularly sheep pens or proximity of sheep, poultry and house martin nests. L. infantum infection rate was 4% for P. ariasi and 0.48% for the total of Larroussius females. P. perniciosus females exhibited an opportunistic behavior, feeding in a wide variety of vertebrate hosts. The high abundance and distribution of proven vector species, together with a canine leishmaniasis seroprevalence of 7.93% in the District, and the capture of a gravid infective sand fly female, suggests that Torres Novas municipality is a potential zoonotic leishmaniasis focus in the country.

Salivary gland transcriptomes and proteomes of Phlebotomus tobbi and Phlebotomus sergenti, vectors of leishmaniasis

Background

Phlebotomus tobbi is a vector of Leishmania infantum, and P. sergenti is a vector of Leishmania tropica. Le. infantum and Le. tropica typically cause visceral or cutaneous leishmaniasis, respectively, but Le. infantum strains transmitted by P. tobbi can cause cutaneous disease. To better understand the components and possible implications of sand fly saliva in leishmaniasis, the transcriptomes of the salivary glands (SGs) of these two sand fly species were sequenced, characterized and compared.

Methodology/Principal Findings

cDNA libraries of P. tobbi and P. sergenti female SGs were constructed, sequenced, and analyzed. Clones (1,152) were randomly picked from each library, producing 1,142 high-quality sequences from P. tobbi and 1,090 from P. sergenti. The most abundant, secreted putative proteins were categorized as antigen 5-related proteins, apyrases, hyaluronidases, D7-related and PpSP15-like proteins, ParSP25-like proteins, PpSP32-like proteins, yellow-related proteins, the 33-kDa salivary proteins, and the 41.9-kDa superfamily of proteins. Phylogenetic analyses and multiple sequence alignments of putative proteins were used to elucidate molecular evolution and describe conserved domains, active sites, and catalytic residues. Proteomic analyses of P. tobbi and P. sergenti SGs were used to confirm the identification of 35 full-length sequences (18 in P. tobbi and 17 in P. sergenti). To bridge transcriptomics with biology P. tobbi antigens, glycoproteins, and hyaluronidase activity was characterized.

Conclusions

This analysis of P. sergenti is the first description of the subgenus Paraphlebotomus salivary components. The investigation of the subgenus Larroussius sand fly P. tobbi expands the repertoire of salivary proteins in vectors of Le. infantum. Although P. tobbi transmits a cutaneous form of leishmaniasis, its salivary proteins are most similar to other Larroussius subgenus species transmitting visceral leishmaniasis. These transcriptomic and proteomic analyses provide a better understanding of sand fly salivary proteins across species and subgenera that will be vital in vector-pathogen and vector-host research.

Phlebotomine female sand flies require a blood meal for egg development, and it is during the blood feeding that pathogens can be transmitted to a host. Leishmania parasites are among these pathogens and can cause disfiguring cutaneous or even possibly fatal visceral disease. The Leishmania parasites are deposited into the bite wound along with the sand fly saliva. The components of the saliva have many pharmacologic and immune functions important in blood feeding and disease establishment. In this article, the authors identify and investigate the protein components of saliva of two important vectors of leishmaniasis, Phlebotomus tobbi and P. sergenti, by sequencing the transcriptomes of the salivary glands. We then compared the predicted protein sequences of these salivary proteins to those of other bloodsucking insects to elucidate the similarity in composition, structure, and enzymatic activity. Finally, this descriptive analysis of P. tobbi and P. sergenti transcriptomes can aid future research in identifying molecules for epidemiologic assays and in investigating sand fly-host interactions.

First report on natural infection of the Phlebotomus tobbi by Leishmania infantum in northwestern Iran

Visceral leishmaniasis (VL) is an important health problem in Ardebil, where it borders Azerbaijan in the northwestern Iran. In spite of the presence of both cutaneous and visceral leishmaniasis (CL and VL) in northwestern Iran, previous researches have consistently revealed the etiologic agent of VL in the region to be Leishmania infantum. This is the first report of natural infection of Phlebotomus tobbi with L. infantum in Bilesavar district in the northern part of Ardebil province bordering Azerbaijan. Polymerase chain reaction (PCR) of kDNA, ITS1-rDNA, and CPB genes of the parasite followed by restriction fragment length polymorphism (RFLP) and gene sequencing analyses revealed presence of L. infantum in six out of 433 tested female sand fly specimens. Although sand flies of P. tobbi were infrequent, two out of 32 (6.25%) females captured in the area were found infected with the parasite. Phlebotomus perfiliewi transcaucasicus, the known vector of VL in the area, were the most dominant species but only four out of 273 (1.47%) tested were infected with L. infantum. This study showed that P. tobbi similar to P. perfiliewi transcaucasicus could play a significant role in the transmission of the L. infantum. However more investigations are needed to demonstrate that L. infantum is the only species circulating in the focus.

Multilocus microsatellite typing (MLMT) of strains from Turkey and Cyprus reveals a novel monophyletic L. donovani sensu lato group

BACKGROUND

New foci of human CL caused by strains of the Leishmania donovani (L. donovani) complex have been recently described in Cyprus and the Çukurova region in Turkey (L. infantum) situated 150 km north of Cyprus. Cypriot strains were typed by Multilocus Enzyme Electrophoresis (MLEE) using the Montpellier (MON) system as L. donovani zymodeme MON-37. However, multilocus microsatellite typing (MLMT) has shown that this zymodeme is paraphyletic; composed of distantly related genetic subgroups of different geographical origin. Consequently the origin of the Cypriot strains remained enigmatic.

METHODOLOGY/PRINCIPAL FINDINGS

The Cypriot strains were compared with a set of Turkish isolates obtained from a CL patient and sand fly vectors in south-east Turkey (Çukurova region; CUK strains) and from a VL patient in the south-west (Kuşadasi; EP59 strain). These Turkish strains were initially analyzed using the K26-PCR assay that discriminates MON-1 strains by their amplicon size. In line with previous DNA-based data, the strains were inferred to the L. donovani complex and characterized as non MON-1. For these strains MLEE typing revealed two novel zymodemes; L. donovani MON-309 (CUK strains) and MON-308 (EP59). A population genetic analysis of the Turkish isolates was performed using 14 hyper-variable microsatellite loci. The genotypic profiles of 68 previously analyzed L. donovani complex strains from major endemic regions were included for comparison. Population structures were inferred by combination of bayesian model-based and distance-based approaches. MLMT placed the Turkish and Cypriot strains in a subclade of a newly discovered, genetically distinct L. infantum monophyletic group, suggesting that the Cypriot strains may originate from Turkey.

CONCLUSION

The discovery of a genetically distinct L. infantum monophyletic group in the south-eastern Mediterranean stresses the importance of species genetic characterization towards better understanding, monitoring and controlling the spread of leishmaniasis in this region.

Prevalence of sand flies and Leishmania donovani infection in a natural population of female Phlebotomus argentipes in Bihar State, India

Leishmaniasis is a vector-borne disease, and in the Indian subcontinent the female Phlebotomus argentipes is the vector for Leishmania donovani. However, data on the extent of sand fly infection rates in natural settings using molecular methods have not been extensively reported in India. In this study a PCR technique was applied targeting the 18S rRNA encoding region to determine the prevalence of Leishmania infection in female P. argentipes captured in the field. For this study, sand flies were collected from 897 houses selected from 50 villages endemic for visceral leishmaniasis (VL) in Muzaffarpur district, Bihar state, using CDC miniature light traps and mouth aspirators. A total of 14,585 sand flies were collected of which 449 were female P. argentipes divided into 132 pools. Molecular detection using PCR targeting the 18S rRNA gene was carried out for the identification of P. argentipes and Leishmania. The overall prevalence of infection was 4.90-17.37% for L. donovani in female P. argentipes in endemic regions of Bihar state. In this study no correlation was found between the presence of infected sand flies and the occurrence of clinical VL. This study provides the first report evaluating the prevalence of Leishmania infection in sand flies in a region endemic for VL in India. Sergentomyia species are the most common species of sand fly. Knowledge of the infection rate in female P. argentipes may help in predicting severity of disease and in vector elimination programs.

Preparation of highly infective Leishmania promastigotes by cultivation on SNB-9 biphasic medium

Protozoan hemoflagellates Leishmania are causative agents of leishmaniases and an important biological model for study of host-pathogen interaction. A wide range of methods of Leishmania cultivation on both biphasic and liquid media is available. Biphasic media are considered to be superior for initial isolation of the parasites and obtaining high promastigote infectivity; however, liquid media are more suitable for large-scale experiments. The aim of the present study was the adaptation and optimization of the cultivation of Leishmania promastigotes on a biphasic SNB-9 (saline-neopeptone-blood 9) medium that was originally developed for Trypanosoma cultivation and combines the advantages of biphasic and liquid media. SNB-9 medium is characterized with a large volume of the liquid phase, which facilitates the manipulation with the culture and provides parasite yields comparable to parasite yields on such liquid medium as Schneider's Insect Medium. We demonstrate that SNB-9 very considerably surpasses Schneider's Insect Medium in in vitro infectivity of the parasites. Additionally, we show that the ratio of apoptotic parasites, which are important for the infectivity of the inoculum, in Leishmania culture in SNB-9 is higher than in Leishmania culture in Schneider's Insect Medium. Thus, we demonstrate that the cultivation of Leishmania on SNB-9 reliably yields highly infective promastigotes suitable for experimental infection.

Experimental transmission of Leishmania infantum by two major vectors: a comparison between a viscerotropic and a dermotropic strain

We quantified Leishmania infantum parasites transmitted by natural vectors for the first time. Both L. infantum strains studied, dermotropic CUK3 and viscerotropic IMT373, developed well in Phlebotomus perniciosus and Lutzomyia longipalpis. They produced heavy late-stage infection and colonized the stomodeal valve, which is a prerequisite for successful transmission. Infected sand fly females, and especially those that transmit parasites, feed significantly longer on the host (1.5–1.8 times) than non-transmitting females. Quantitative PCR revealed that P. perniciosus harboured more CUK3 strain parasites, while in L. longipalpis the intensity of infection was higher for the IMT373 strain. However, in both sand fly species the parasite load transmitted was higher for the strain with dermal tropism (CUK3). All but one sand fly female infected by the IMT373 strain transmitted less than 600 promastigotes; in contrast, 29% of L. longipalpis and 14% of P. perniciosus infected with the CUK3 strain transmitted more than 1000 parasites. The parasite number transmitted by individual sand flies ranged from 4 up to 4.19×10⁴ promastigotes; thus, the maximal natural dose found was still about 250 times lower than the experimental challenge dose used in previous studies. This finding emphasizes the importance of determining the natural infective dose for the development of an accurate experimental model useful for the evaluation of new drugs and vaccines.

Leishmaniasis is a disease caused by protozoan parasites which are transmitted through the bites of infected insects called sand flies. The World Health Organization has estimated that leishmaniases cause 1.6 million new cases annually, of which an estimated 1.1 million are cutaneous or mucocutaneous, and 500,000 are visceral, the most severe form of the disease and fatal if left untreated. The development of a more natural model is crucial for the evaluation of new drugs or vaccine candidates against leishmaniases. The main aim of this study was to quantify the number of Leishmania infantum parasites transmitted by a single sand fly female into the skin of a vertebrate host (mouse). Two L. infantum strains, viscerotropic IMT373 and dermotropic CUK3, were compared in two natural sand fly vectors: Phlebotomus perniciosus and Lutzomyia longipalpis. We found that the parasite number transmitted by individual sand flies ranged from 4 up to 4.19×10⁴. The maximal natural infective dose found in our experiments was about 250 times lower than the experimental challenge dose used in most previous studies.

Seasonal dynamics and altitudinal distributions of sand fly (Diptera: Psychodidae) populations in a cutaneous leishmaniasis endemic area of the Cukurova region of Turkey

This paper presents the results of an entomological survey in an endemic focus of cutaneous leishmaniasis in the Cukurova region of Turkey. A total of 8,927 specimens belonging to eight Phlebotomus and two Sergentomyia species were captured with sticky papers and CDC light traps from 52 stations. Phlebotomus tobbi Adler, was found to be the most abundant species. Sand fly activity started in May and ended in October. Abundance was highest in August. According to the frequency distributions among certain temperature intervals the observed number of individuals was significantly different from the expected values between 22-24° C and 28-30° C. There was no significant correlation between the abundance of sand flies and altitude. However, sand fly species showed great aggregation at the 100-199 m and 200-299 m altitude intervals. The Shannon-Weinner index indicated no difference between the diversity and abundance of sand flies at different altitudes. Diversity and evenness reached maximum values at 500 m. Jaccard's coefficient indicated that similarity was the highest between 0-99 and 300-399, 0-99 and 500-599 and 100-199 and 200-299 m and lowest between 100-199 and 300-399 and 100-199 and 500-599 m.

Genetic structures of sand fly (Diptera: Psychodidae) populations in a leishmaniasis endemic region of Turkey

The object of this study was to determine the genetic structures of three vector species, Phlebotomus tobbi, Phlebotomus papatasi, and Phlebotomus sergenti, in the Cukurova Region of Turkey, an endemic focus of cutaneous leishmaniasis. The genetic diversity indices, neutrality tests and hierarchical analysis of molecular variance (AMOVA) were performed using partial sequences of ITS2 and cytochrome b gene regions. In all species, within population genetic variation was higher than between population variation for ITS2 gene region. Fst values were low and non-significant for P. sergenti, and were higher for P. papatasi and P. tobbi indicating a weak structuring between populations. AMOVA tests suggest any substantial isolation between populations within species. AMOVA analysis of cyt b gene region revealed significant genetic structuring between populations for P. papatasi and P. sergenti. Fst values were relatively high and significant for these species indicating a certain degree of isolation between populations. However, in P. tobbi, any significant population genetic structuring was detected. Tajima's D and Fu's Fs values were negative and significant in all three species might be indicating a demographic expansion.

Molecular approaches for a better understanding of the epidemiology and population genetics ofLeishmania

Molecular approaches are being used increasingly for epidemiological studies of visceral and cutaneous leishmaniases. Several molecular markers resolving genetic differences betweenLeishmaniaparasites at species and strain levels have been developed to address key epidemiological and population genetic questions. The current gold standard, multilocus enzyme typing (MLEE), needs cultured parasites and lacks discriminatory power. PCR assays identifying species directly with clinical samples have proven useful in numerous field studies. Multilocus sequence typing (MLST) is potentially the most powerful phylogenetic approach and will, most probably, replace MLEE in the future. Multilocus microsatellite typing (MLMT) is able to discriminate below the zymodeme level and seems to be the best candidate for becoming the gold standard for distinction of strains. Population genetic studies by MLMT revealed geographical and hierarchic population structure inL. tropica, L. majorand theL. donovanicomplex. The existence of hybrids and gene flow betweenLeishmaniapopulations suggests that sexual recombination is more frequent than previously thought. However, typing and analytical tools need to be further improved. Accessible databases should be created and sustained for integrating data obtained by different researchers. This would allow for global analyses and help to avoid biases in analyses due to small sample sizes.

Leishmaniasis in an era of conflict in the Middle East

Leishmaniasis is endemic in the Middle East, and both cutaneous and visceral forms are reported from the region ranging from the Levant to Afghanistan. The potential and proven phlebotomine sand fly vectors and reservoir hosts of the Leishmaniases species in Afghanistan, Iran, Iraq, Israel, Jordan, Lebanon, Saudi Arabia, Syria, Turkey, and Yemen are described. This region has seen a movement of populations across the area, due to both military and civilian strife. Refugees, armed forces, and multi-national contractors are particularly at risk to acquire this disease. There has been an upsurge in Leishmaniasis research, especially as new foci are exposed and the need to protect the naïve populations moving into endemic areas becomes a public health priority. New sand fly vectors and animal reservoirs have been discovered while novel control methods are being evaluated. Modern molecular techniques are now being used more routinely and revealing some unusual findings. The aim of this review is to collate the most recent data on the burden of the disease, diagnostic applications, eco-epidemiology of vectors, and reservoir hosts, and how the control projects have been developing in the Middle East.

Specificity of anti-saliva immune response in mice repeatedly bitten by Phlebotomus sergenti

Sand flies are bloodsucking insects transmitting parasites of genus Leishmania, the causative agents of diseases in humans and dogs. Experimental hosts repeatedly exposed to sand fly saliva can control Leishmania infection. Cell-mediated anti-saliva immune response is most likely responsible for this protective effect; however, there is no study so far concerning its antigenic specificity towards different sand fly vectors. In this study, splenocytes from BALB/c mice repeatedly exposed to the bites of Phlebotomus sergenti were challenged ex vivo with salivary gland homogenates from three different sand fly vectors -P. sergenti, P. papatasi, or P. arabicus. Mice bitten by P. sergenti had higher proliferative response to homologous antigen than splenocytes from naive mice. Splenocytes from P. sergenti bitten mice as well as anti-P. sergenti antibodies partially cross-reacted with P. papatasi saliva. In contrast, no cross-reactivity was found with P. arabicus saliva. Our data indicate that both arms of the immune system, cellular and humoral, react in a species-specific manner. Therefore, the presence of antibodies against salivary components of a certain species indicates the specificity of cell-mediated immune response as well. The data suggest that unique transmission-blocking vaccine would be required for each vector -Leishmania combination.

The role of host genetics in leishmaniasis

Leishmaniasis is one of the world's important infectious diseases. It is prevalent in tropical and subtropical regions of the world and endemic in 88 countries, with two million new cases of leishmaniasis reported annually. As a complex disease, the pathology of leishmaniasis varies and is determined by factors such as the environment, the insect vector, and parasite and host genetics. The contributing host genetics involve multiple genes; thus, the mouse model of leishmaniasis has been exploited extensively in an attempt to identify and dissect the contribution of disease modifier genes to pathogenesis. This review summarizes recent advances in the identification of genetic loci involved in the host response to Leishmania spp. in the mouse model and in the human situation.