Host preference and Leishmania infantum natural infection of the sand fly Phlebotomus perfiliewi in northern Italy

Genomic and epidemiological evidence for the emergence of a L. infantum/L. donovani hybrid with unusual epidemiology in northern Italy

Leishmania (L.) infantum is one of the main causative agents of animal and human leishmaniasis across many endemic areas in South America, Europe, North Africa, and Asia. Despite its clinical significance, little is known about the genetic diversity of L. infantum circulating in a given endemic area. Here, we investigate this important open question by applying a comparative genomics approach to seven L. infantum isolates from different hosts and Italian regions, including the northern part of the country (Emilia-Romagna, RER), Sicily, and Sardinia, as an initial attempt to explore the breadth of parasite genetic heterogeneity in Italy. Additionally, microsatellite analysis was carried out to compare the isolates from RER with other 70 L. infantum strains from the same region as well as 65 strains belonging to the L. donovani complex from other countries. We revealed important karyotypic instability and identified strain-specific changes in gene dosage, which affected important virulence factors such as amastins and surface antigen-like proteins. Single nucleotide polymorphism-based clustering analysis of these genomes together with over 80 publicly available L. infantum and L. donovani genomes placed the Italian isolates into three geographically distinct clusters within the Mediterranean basin and uncovered three isolates clustering with putative L. infantum/L. donovani hybrids isolated in Cyprus. As judged by microsatellite profiling, these hybrid isolates are representative of a sub-population of parasites circulating in northern Italy that preferentially infect humans but not dogs. Our results place Italy at the crossroads of L. infantum infection in the Mediterranean and call attention to the public health risk represented by the introduction of non-European Leishmania species.IMPORTANCEThis study closes important knowledge gaps with respect to Leishmania (L.) infantum genetic heterogeneity in a given endemic country, as exemplified here for Italy, and reveals genetic hybridization as a main cause for re-emerging human leishmaniasis in northern Italy. The observed high diversity of Leishmania parasites on the Italian peninsula suggests different geographical origins, with genomic adaptation to various ecologies affecting both pathogenicity and transmission potential. This is documented by the discovery of a putative L. infantum/L. donovani hybrid strain, which has been shown to preferentially infect humans but not dogs. Our results provide important information to health authorities, which need to consider the public health risk represented by the introduction of new Leishmania species into EU countries due to population displacement or travel from countries where exotic/allochthonous parasite species are endemic.

Meteorological, demographic, and environmental risk factors for Leishmania infantum in wildlife

Leishmania infantum is an important and neglected vector-borne zoonotic protozoa endemic in the Mediterranean basin. Several wild and domestic mammals can contribute to maintaining its circulation but their importance as effective reservoirs is still under discussion and varies depending on local ecological communities. By combining environmental, climatic, and individual information, this study assessed the presence of L. infantum DNA in a set of wild species from Northwestern Italy and the potential ecological factors related to the risk of infection. From 2020 to 2022, 304 free-ranging wild animals were analyzed for the detection of L. infantum DNA in the spleen and popliteal lymph node (when available). The prevalence obtained in wild boar (Sus scrofa) and roe deer (Capreolus capreolus) was higher than those previously reported (% ± confidence interval 95%; 42.9 ± 18.4% and 27 ± 6.6% in wild boar and roe deer, respectively), and this is the first report of this parasite infecting the coypu Myocastor coypus (60 ± 34.7%). L. infantum DNA was detected in all the seasons including those free of adult sandflies and seasonal differences were minimal, suggesting a long course of infection. The models revealed that animals from rainy areas with higher greenness during the summer, highly populated by humans and predominantly covered by water surfaces had a higher risk of L. infantum. This study contributes to confirming previous findings on the existence of a sylvatic cycle for L. infantum in certain regions of Italy, as well as on the potential epidemiological role of roe deer for this parasite given the elevated prevalence found.

Smelly interactions: host-borne volatile organic compounds triggering behavioural responses in mosquitoes, sand flies, and ticks

Volatile organic compounds (VOCs) are chemicals emitted as products of cell metabolism, which reflects the physiological and pathological conditions of any living organisms. These compounds play a key role as olfactory cues for arthropod vectors such as mosquitoes, sand flies, and ticks, which act in the transmission of pathogens to many animal species, including humans. Some VOCs may influence arthropod behaviour, e.g., host preference and oviposition site selection for gravid females. Furthermore, deadly vector-borne pathogens such as Plasmodium falciparum and Leishmania infantum are suggested to manipulate the VOCs profile of the host to make them more attractive to mosquitoes and sand fly vectors, respectively. Under the above circumstances, studies on these compounds have demonstrated their potential usefulness for investigating the behavioural response of mosquitoes, sand flies, and ticks toward their vertebrate hosts, as well as potential tools for diagnosis of vector-borne diseases (VBDs). Herein, we provide an account for scientific data available on VOCs to study the host seeking behaviour of arthropod vectors, and their usefulness as attractants, repellents, or tools for an early diagnosis of VBDs.

Monitoring of Insecticide Resistance Mutations and Pathogen Circulation in Sand Flies from Emilia-Romagna, a Leishmaniasis Endemic Region of Northern Italy

The continuously expanding distribution of sand flies, proven vectors of Leishmania and of several phleboviruses, is a growing public health issue in Europe. Especially in Italy, visceral leishmaniasis (VL) is occurring with increasing incidence northward, in previously non-endemic provinces. Around the globe, disease elimination efforts largely focus on sand fly vector insecticidal control, often leading to the development of resistance. In Emilia-Romagna (ER), northern Italy, insecticides are heavily applied for agricultural and mosquito control, but not specifically against sand flies. Here, we investigated the sand fly species composition in certain environmental settings in ER provinces and monitored the presence of pyrethroid resistance mutations and pathogen circulation. Phlebotomus perfiliewi, a dominant vector of Leishmania infantum, was detected almost exclusively in the region. No mutations in the voltage-gated sodium channel gene, e.g., knock-down resistance mutations I1011M, L1014F/S, V1016G, or F1020S, were recorded. Pathogen monitoring revealed that almost 40% of the tested sand fly pools were positive for Leishmania, while the presence of Toscana and Fermo phleboviruses was also observed in much lower frequencies (≤3% positive pools). Regular epidemiological and entomological monitoring, alongside resistance surveillance, is highly recommended to ensure the sustainability and efficiency of vector control interventions.

Serological and Molecular Survey of Leishmania infantum in a Population of Iberian Lynxes (Lynx pardinus)

Leishmania infantum, the sand fly-transmitted protozoan parasite responsible for leishmaniasis in humans, dogs, and cats, is endemic in the Iberian Peninsula. However, the impact of L. infantum infection on the conservation of the endangered Iberian lynx (Lynx pardinus) is unknown. Herein, we describe for the first time the occurrence of L. infantum infection among a population of reintroduced and wild-born L. pardinus living in the Portuguese Guadiana Valley Park. The presence of infection was addressed by molecular detection of Leishmania kinetoplast DNA (kDNA) in 35 lynxes, with further confirmation of L. infantum species performed by an internally transcribed spacer (ITS)-1 sequencing. Eight blood samples were positive for kDNA, and ITS-1 sequencing confirmed the presence of L. infantum in two of those samples. Exposure to Leishmania was screened in a group of 36 lynxes using an immunofluorescence antibody test (IFAT) and a multi-antigen enzyme-linked immunosorbent assay (ELISA), using SPLA, rK39, and CPX as Leishmania-specific antigens. Four animals presented a positive IFAT at a dilution of 1:40. Eight samples were considered seropositive to all ELISA Leishmania-specific antigens. Agreement between PCR, IFAT, and all ELISA antigens was found for 1 in 27 samples. These results highlight the susceptibility of autochthonous L. pardinus to L. infantum infection. Further investigation is required to assess the impact of L. infantum infection on this wild species conservation.

Wildlife Hosts of Leishmania infantum in a Re-Emerging Focus of Human Leishmaniasis, in Emilia-Romagna, Northeast Italy

In the last decade, an upsurge of human leishmaniasis has been reported in the Emilia-Romagna region, Northeast Italy. Epidemiologic data have raised doubts about the role of dogs as the main reservoirs for Leishmania infantum. In the present study, a total of 1,077 wild animals were screened for L. infantum DNA in earlobe and spleen samples from 2019 to 2022. The lymph nodes were tested only in 23 animals already positive in the earlobe and/or spleen. A total of 71 (6.6%) animals resulted positive in at least one of the sampled tissues, including 3/18 (16.7%) wolves, 6/39 (15.4%) European hares, 38/309 (12.3%) roe deer, 1/11 (9.1%) red deer, 8/146 (4.9%) wild boars, 13/319 (4.1%) red foxes, 1/54 (1.9%) porcupine, and 1/59 (1.7%) European badger. Most of the infected animals (62/71) tested positive only in the earlobe tissue, only four animals (two roe deer and two wild boars) tested positive only in the spleen, and five animals (three roe deer and two red foxes) resulted positive for both tissues. L. infantum DNA was detected in the lymph nodes of 6/23 animals. L. infantum detection occurred in all seasons associated with low real-time PCR Ct values. Further research is needed in order to clarify the role of wildlife in the re-emerging focus of leishmaniasis in Northeast Italy.

Roe deer (Capreolus capreolus) are a novel potential reservoir for human visceral leishmaniasis in the Emilia-Romagna region of northeastern Italy

Leishmaniasis is a complex human disease caused by intracellular parasites of the genus Leishmania, predominantly transmitted by the bite of sand flies. In Italy, leishmaniasis is caused exclusively by Leishmania infantum, responsible for the human and canine visceral leishmaniases (HVL and CVL, respectively). Within the Emilia-Romagna region, two different foci are active in the municipalities of Pianoro and Valsamoggia (both in the province of Bologna). Recent molecular studies indicated that L. infantum strains circulating in dogs and humans are different, suggesting that there is an animal reservoir other than dogs for human visceral leishmaniasis in the Emilia-Romagna region. In this work, we analyzed specimens from wild animals collected during hunts or surveillance of regional parks near active foci of human visceral leishmaniasis for L. infantum infection in the province of Bologna. Out of 70 individuals analyzed, 17 (24%) were positive for L. infantum. The infection prevalence in hedgehogs (Erinaceus europaeus), roe deer (Capreolus capreolus), badgers (Meles meles), and bank voles (Myodes glareolus) was 80, 33, 25, and 11%, respectively. To distinguish the two strains of L. infantum we have developed a nested PCR protocol optimized for animal tissues. Our results demonstrated that most (over 90%) of L. infantum infections in roe deer were due to the strain circulating in humans in the Emilia-Romagna region.

Detection of Leishmania sp. kDNA in questing Ixodes ricinus (Acari, Ixodidae) from the Emilia-Romagna Region in northeastern Italy

To date, sand flies (Phlebotominae) are the only recognized biological vectors of Leishmania infantum, the causative agent of human visceral leishmaniasis, which is endemic in the Mediterranean basin and also widespread in Central and South America, the Middle East, and Central Asia. Dogs are the main domestic reservoir of zoonotic visceral leishmaniasis, and the role of secondary vectors such as ticks and fleas and particularly Rhipicephalus sanguineus (the brown dog tick) in transmitting L. infantum has been investigated. In the present paper, the presence of Leishmania DNA was investigated in questing Ixodes ricinus ticks collected from 4 rural areas included in three parks of the Emilia-Romagna Region (north-eastern Italy), where active foci of human visceral leishmaniasis have been identified. The analyses were performed on 236 DNA extracts from 7 females, 6 males, 72 nymph pools, and 151 larvae pools. Four samples (1.7%) (i.e., one larva pool, 2 nymph pools, and one adult male) tested positive for Leishmania kDNA. To the best of our knowledge, this is the first report of the presence of Leishmania kDNA in questing I. ricinus ticks collected from a rural environment. This finding in unfed larvae, nymphs, and adult male ticks supports the hypothesis that L. infantum can have both transstadial and transovarial passage in I. ricinus ticks. The potential role of I. ricinus ticks in the sylvatic cycle of leishmaniasis should be further investigated.