Leishmaniasis in Norway Rats in Sewers, Barcelona, Spain

Analysis of the current risk of Leishmania infantum transmission for domestic dogs in Spain and Portugal and its future projection in climate change scenarios

Canine leishmaniosis, caused by the protozoan parasite Leishmania infantum, is a cosmopolitan vector-borne zoonosis, transmitted principally by Phlebotomus perniciosus in Spain and Portugal, where it is considered an endemic disease. Ecoinformatics tools such as ecological niche models (ENM) have been successfully tested to model the distribution of the risk of infection of different parasitosis as they take into account environmental variables vital for their survival. The risk map proposed in this study combines the potential distribution of Ph. perniciosus in the Iberian Peninsula and the calculation of the infection rate of the parasite in the vector to model the risk of contracting the disease in a more realistic way. In fact, this weighting strategy improves the predictive power of the resulting model (R2 = 0.42, p = < 0.01) compared to the Ph. perniciosus ENM model alone (R2 = 0.13, p > 0.05). The places with the highest risk of transmission are the southwest and central peninsular area, as well as the Mediterranean coast, the Balearic Islands and the Ebro basin, places where the ideal habitat of Ph. perniciosus and the infection rate is also high. In the case of future projections under climate change scenarios, an increase in the risk of infection by L. infantum can be observed in most of the territory (4.5% in 2040, 71.6% in 2060 and 63% in 2080), mainly in the northern part of the peninsula. The use of ENMs and their weighting with the infection rate in Ph. perniciosus is a useful tool in predicting the risk of infection for L. infantum in dogs for a given area. In this way, a more complete model can be obtained to facilitate prevention and control.

Parasite Fauna and Coinfections in Urban Rats Naturally Infected by the Zoonotic Parasite Angiostrongylus cantonensis

When the zoonotic parasite of rodents that can cause human neuroangiostrongyliasis, i.e., Angiostrongylus cantonensis, is found in its natural definitive hosts, it is usually reported in isolation, as if the rat lungworm were the only component of its parasite community. In this study, we report the coinfections found in rats naturally infected by A. cantonensis in urban populations of Rattus norvegicus and Rattus rattus in Valencia, Spain. In addition to the rat lungworms, which were found in 14 of the 125 rats studied (a prevalence of 11.20%), 18 other parasite species (intestinal and tissular protists, microsporidia and helminths) were found, some of them with high burdens. Fourteen of these nineteen species found are potential zoonotic parasites, namely Blastocystis, Giardia duodenalis, Cryptosporidium spp., Enterocytozoon bieneusi, Encephalitozoon hellem, Toxoplasma gondii, Brachylaima spp., Hydatigera taeniaeformis s.l. larvae, Hymenolepis nana, Hymenolepis diminuta, Angiostrongylus cantonensis, Calodium hepaticum, Gongylonema neoplasticum and Moniliformis moniliformis. The total predominance of coinfected rats as well as their high parasite loads seem to indicate a trend towards parasite tolerance.

Is leishmaniasis the new emerging zoonosis in the world?

Leishmania is a genus of parasitic protozoa that causes a disease called leishmaniasis. Leishmaniasis is transmitted to humans through the bites of infected female sandflies. There are several different species of Leishmania that can cause various forms of the disease, and the symptoms can range from mild to severe, depending on species of Leishmania involved and the immune response of the host. Leishmania parasites have a variety of reservoirs, including humans, domestic animals, horses, rodents, wild animals, birds, and reptiles. Leishmaniasis is endemic of 90 countries, mainly in South American, East and West Africa, Mediterranean region, Indian subcontinent, and Central Asia. In recent years, cases have been detected in other countries, and it is already an infection present throughout the world. The increase in temperatures due to climate change makes it possible for sandflies to appear in countries with traditionally colder regions, and the easy movement of people and animals today, facilitate the appearance of Leishmania species in new countries. These data mean that leishmaniasis will probably become an emerging zoonosis and a public health problem in the coming years, which we must consider controlling it from a One Health point of view. This review summarizes the prevalence of Leishmania spp. around the world and the current knowledge regarding the animals that could be reservoirs of the parasite.

Survey on the presence of Leishmania sp. in peridomestic rodents from the Emilia-Romagna Region (North-Eastern Italy)

Leishmaniasis is a neglected vector-borne parasitic disease caused in Italy only by the species Leishmania infantum of the Leishmania donovani complex, which is the causative agent of the zoonotic visceral leishmaniasis (VL) and the sporadic cutaneous leishmaniasis (CL) in humans, and of the canine leishmaniasis (CanL). The disease is considered endemic in southern, central, and insular Italian regions and recognizes phlebotomine sand flies as vector and dogs as main reservoir. Among northern Italian region, Emilia-Romagna shows peculiar epidemiological situation and recent studies are questioning the role of dog as main reservoir of L. infantum. Due to their synanthropic relationship with humans, rodents have been tested for Leishmania spp. in several European countries. The aim of this study was to assess the presence of Leishmania spp. in peridomestic rodents in the Emilia-Romagna. The study was carried out on 136 peridomestic rodents collected by professional pest control services: 47 brown rats (Rattus norvegicus), 39 black rats (Rattus rattus) and 50 mice (Mus musculus). Specimens of earlobe skin, spleen, liver and prescapular lymph nodes were tested with a real-time PCR. Fifteen (11%) rodents, tested positive for Leishmania spp. in particular five brown rats (10.6%), five black rats (12.8%) and five mice (10%). Positivity was obtained from different target organs. These findings revealed the presence of Leishmania spp. in peridomestic rodents of Emilia-Romagna Region, also in two species never tested before in Italy, namely R. norvegicus and M. musculus.

Wild micromammal host spectrum of zoonotic eukaryotic parasites in Spain. Occurrence and genetic characterisation

Micromammals have historically been recognized as highly contentious species in terms of the maintenance and transmission of zoonotic pathogens to humans. Limited information is currently available on the epidemiology and potential public health significance of intestinal eukaryotes in wild micromammals. We examined 490 faecal samples, grouped into 155 pools, obtained from 11 micromammal species captured in 11 Spanish provinces for the presence of DNA from Cryptosporidium spp., Giardia duodenalis, Enterocytozoon bieneusi and Blastocystis sp. The presence of Leishmania spp. was investigated in individual spleen samples. All micromammal species investigated harboured infections by at least one eukaryotic parasite, except Apodemus flavicollis, Myodes glareolus, Sorex coronatus and Sciurus vulgaris, but the sample size for these host species was very low. Cryptosporidium spp. was the most prevalent species found (3.7%, 95% confidence interval [CI]: 2.2-5.7), followed by G. duodenalis (2.8%, 95% CI: 1.6-4.6) and E. bieneusi (2.6%, 95% CI: 1.4-4.3). All pooled faecal samples tested negative for Blastocystis sp. Leishmania infantum was identified in 0.41% (95% CI: 0.05-1.46) of the 490 individual spleen samples analysed. Sequence analyses allowed the identification of Cryptosporidium andersoni (5.9%), C. ditrichi (11.7%), C. muris (5.9%), C. parvum (5.9%), C. tyzzeri (5.9%), rat genotypes CR97 (5.9%) and W19 (5.9%), vole genotypes V (11.7%) and VII (5.9%) and Cryptosproridium spp. (35.3%) within Cryptosporidium (n = 17). Known genotypes C (66.7%) and Peru11 (25.0%) and a novel genotype (named MouseSpEb1, 8.3%) were detected within E. bieneusi (n = 12). None of the G. duodenalis-positive samples could be genotyped at the assemblage level. Molecular data indicate that wild micromammals were primarily infected by rodent-adapted species/genotypes of eukaryotic pathogens and thereby have a limited role as a source of human infections. The presence of ruminant-adapted species C. andersoni along with finding C. parvum is indicative of an overlap between domestic/peri-domestic and sylvatic transmission cycles of these agents.

Molecular detection of Leishmania infantum in rats and sand flies in the urban sewers of Barcelona, Spain

Background

Classically, dogs have been considered to be the only reservoir of leishmaniasis in urban areas. However, in a previous study, we found a 33.3% prevalence of Leishmania infantum in the spleens of Norway rats (Rattus norvegicus) sampled in the underground sewer system of the city of Barcelona (Spain). The aim of the present study was to verify, using molecular methods, the potential reservoir role of these rats in the same sewer system.

Methods

A sensitive real-time PCR (qPCR) assay, DNA sequencing and phylogenetic analysis were carried out to identify and quantify the presence of L. infantum DNA in sand fly individuals captured in the same underground sewer system of Barcelona as in our previous study and in the spleens and ears of rats captured in the same sewer system.

Results

Leishmania infantum DNA was found in 14 of the 27 (51.9%) sand flies identified as Phlebotomus perniciosus, and 10 of the 24 (41.7%) rats studied were infected. Leishmania infantum was found in the spleens (70%) and in the ears (40%) of the infected rats. Quantitative results revealed the presence of high loads of L. infantum in the rats studied (> 3 × 10⁶ parasites/g ear tissue) and among the sand flies (> 34 × 10⁶ parasites in 1 individual).

Conclusions

The molecular methods used in this study demonstrated a high prevalence of L. infantum in the underground sewer populations of both R. norvegicus and P. perniciosus. These results suggest that sewer rats, in addition to dogs, are likely to act as reservoirs of leishmaniasis in cities, where sewer systems seem to offer the ideal scenario for the transmission of leishmaniasis. Therefore, to achieve the WHO 2030 target on the elimination of leishmaniasis as a public health problem successfully, an efficient control strategy against leishmaniasis in rats and sand flies should be implemented, particularly in the sewer systems of urban areas of endemic countries.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05309-4.

Leishmaniosis in Rodents Caused by Leishmania infantum: A Review of Studies in the Mediterranean Area

Leishmaniosis infection begins when a phlebotomine sand fly vector inoculates pathogenic protozoan parasites of the genus Leishmania into a mammalian host. In the case of Leishmania infantum, the domestic dog is considered to be the main parasite reservoir, and canine leishmaniosis (CanL) has a high mortality rate in untreated dogs. Hundreds of cases of human leishmaniosis (HL) are reported in the world each year, the incidence in Europe being relatively low. Leishmaniosis control is primarily focused on the dog, combining methods that prevent sand fly bites and boost host resistance to infection. However, these measures are only partially effective and new solutions need to be found. One of the main factors limiting CanL and HL control is the existence of a sylvatic Leishmania transmission cycle that interacts with the domestic cycle maintained by dogs. It is suspected that the main reservoir of infection in wildlife are rodents, whose expansion and rapid population growth worldwide is increasing the risk of human and zoonotic pathogen transfer. The aim of this review is therefore to analyze reports in the literature that may shed light on the potential role of rodents in the leishmaniosis transmission cycle in the Mediterranean area. Following the general methodology recommended for reviews, six databases (Google Scholar, Ovid, PubMed, Science Direct, Scopus and Web of Science) were explored for the period January 1995 to December 2020. The results extracted from 39 publications that met the established inclusion criteria were analyzed. It was found that 23 species of rodents have been studied in nine countries of the Mediterranean basin. Of the 3,643 specimens studied, 302 tested positive for L. infantum infection by serology, microscopy and/or molecular techniques.

Cutaneous and Mucocutaneous Leishmaniasis

Leishmaniasis is a chronic disease caused by flagellate protozoa of the genus Leishmania. It is a global disease, but most cases are seen in South America, the Mediterranean, and some areas of Asia and Africa. The 3 main types of leishmaniasis are cutaneous (the most common), mucocutaneous, and visceral (the most severe). Visceral leishmaniasis is also known as kala-azar. Leishmaniasis is diagnosed by demonstrating the presence of Leishmania amastigotes in clinical specimens using direct microscopic examination or molecular analysis. Various treatments exist, although the evidence supporting the options available for cutaneous leishmaniasis is weak. Both the classical presentation of leishmaniasis and our management of the disease have changed in recent decades because of acquired immune deficiency caused by conditions such as human immunodeficiency infection or the use of tumor necrosis factor inhibitors.

Trends in the Epidemiology of Leishmaniasis in the City of Barcelona (1996-2019)

Background: Leishmaniasis is a neglected zoonosis produced by 20 different flagellated parasites of the Leishmania genus, a protozoan transmitted to humans and other vertebrates by the bite of dipteran insects of the Phlebotominae subfamily. It is endemic in Mediterranean countries and the number of cases is expected to increase due to climate change and migration. Prioritizing public health interventions for prevention and control is essential. The objective was to characterize the epidemiology and temporal trends in the incidence of human leishmaniasis in the city of Barcelona, between the years 1996 and 2019. Methods: A population-based, analytical observational study among residents in the city of Barcelona was conducted of all the cases of leishmaniasis reported between 1996 and 2019 to the Public Health Agency. The epidemiological survey contains clinical, diagnostic, and epidemiological data, including contact with suspicious mammals or insects. Annual incidence-rates were calculated by sex, age, and country of origin. Chi-square tests were used to assess association between studied risk factors, periods of time and type of leishmaniasis. Results: During the study period a total of 177 cases of leishmaniasis were reported in Barcelona, being 74.6% (n = 132) of the total cases in Spanish born, although within the foreign-born population the incidence was higher. Median age was 34 years (IQR = 10-48) and 121 (66.8%) were male. The main type was cutaneous (46%) followed by visceral (35.1%). The cumulative incidence was 0.47 per 100,000 inhabitants, with the highest incidence found in 2017 (1.60 per 100,000 inhabitants). A higher incidence was observed in the 0-4-year-old group (1.73 per 100,000 inhabitants), but increased during the study period for all age groups. There was an increase of foreign origin cases, and a decrease in the number of cases associated to any immunosuppression. Conclusion: In Barcelona, leishmaniasis incidence continues to be higher in people under 5 years of age, and 25-64 years old males, but it has also increased in population from foreign country of birth. There is an increase of the cases since 2016, probably due to the changes in the notification system, increasing the diagnosis of cutaneous leishmaniasis. Improvements in the current surveillance system are needed. Notification of the disease, vector, and reservoir control activities are also essential for the control of the disease.

One Health Approach to Zoonotic Parasites: Molecular Detection of Intestinal Protozoans in an Urban Population of Norway Rats, Rattus norvegicus, in Barcelona, Spain

Rattus norvegicus, the brown or Norway rat, is the most abundant mammal after humans in urban areas, where they live in close proximity to people. Among rodent-borne diseases, the reservoir role of Norway rats of zoonotic parasites in cities has practically been ignored. Considering the parasitic diseases in the One Health approach, we intended to identify and quantify the zoonotic intestinal protozoans (ZIP) in an urban population of R. norvegicus in the city of Barcelona, Spain. We studied the presence of ZIP in 100 rats trapped in parks (n = 15) as well as in the city’s sewage system (n = 85) in the winter of 2016/17. The protozoans were molecularly identified by means of a multiplex PCR (Allplex^TM Gastrointestinal Panel-Parasite Assay). We also investigated the presence of co-infections among the species found. Four ZIP were identified, presenting significant prevalences in sewers, specifically Blastocystis (83.5%), Giardia duodenalis (37.7%), Cryptosporidium spp. (34.1%), and Dientamoeba fragilis (14.1%). Several co-infections among the detected ZIP were also detected. The reservoir role of ZIP that Norway rats play in cities as well as the role rats may play as sentinels of zoonotic parasites affecting humans in urban areas are strongly backed up by our findings. The increasing worldwide urbanization, climate change, and the COVID-19 pandemic are factors that are producing an increase in human–rat interactions. Our results should be considered a warning to the authorities to intensify rat control and surveillance in public health interventions.

New Epidemiological Aspects of Animal Leishmaniosis in Europe: The Role of Vertebrate Hosts Other Than Dogs

Infection with Leishmania parasites can lead to severe disease in humans and dogs, which act as a reservoir in zoonotic transmission. An increasing number of reports suggest that leishmaniosis is not restricted to dogs, but also affects many other mammalian and avian species. Consequently, this expands the potential reservoir and is of great public and veterinary health concern. The present study reviews, based on a comprehensive search of scientific literature published from 1 January 2001 to 31 December 2020, the currently available information on animal leishmaniosis in vertebrates in Europe, other than dogs and humans. This review provides an exhaustive list of mammals and birds in which infections with or exposure to Leishmania parasites have been detected in European countries. Most cases are reported from the Mediterranean region. Domestic animals, in particular cats, pose a concern because of close contact with humans. The wildlife reservoir is less likely to contribute to zoonotic transmission, with the exception of hares. This potentially large reservoir needs to be taken into account when developing control measures for zoonotic leishmaniosis. From a veterinary point of view, it is important that veterinarians are better aware of leishmaniosis and trained in its management.

Occurrence and Genetic Diversity of Protist Parasites in Captive Non-Human Primates, Zookeepers, and Free-Living Sympatric Rats in the Córdoba Zoo Conservation Centre, Southern Spain

Little information is currently available on the epidemiology of parasitic and commensal protist species in captive non-human primates (NHP) and their zoonotic potential. This study investigates the occurrence, molecular diversity, and potential transmission dynamics of parasitic and commensal protist species in a zoological garden in southern Spain. The prevalence and genotypes of the main enteric protist species were investigated in faecal samples from NHP (n = 51), zookeepers (n = 19) and free-living rats (n = 64) by molecular (PCR and sequencing) methods between 2018 and 2019. The presence of Leishmania spp. was also investigated in tissues from sympatric rats using PCR. Blastocystis sp. (45.1%), Entamoeba dispar (27.5%), Giardia duodenalis (21.6%), Balantioides coli (3.9%), and Enterocytozoon bieneusi (2.0%) (but not Troglodytella spp.) were detected in NHP. Giardia duodenalis (10.5%) and Blastocystis sp. (10.5%) were identified in zookeepers, while Cryptosporidium spp. (45.3%), G. duodenalis (14.1%), and Blastocystis sp. (6.25%) (but not Leishmania spp.) were detected in rats. Blastocystis ST1, ST3, and ST8 and G. duodenalis sub-assemblage AII were identified in NHP, and Blastocystis ST1 in zookeepers. Giardia duodenalis isolates failed to be genotyped in human samples. In rats, four Cryptosporidium (C. muris, C. ratti, and rat genotypes IV and V), one G. duodenalis (assemblage G), and three Blastocystis (ST4) genetic variants were detected. Our results indicate high exposure of NHP to zoonotic protist species. Zoonotic transmission of Blastocysts ST1 was highly suspected between captive NHP and zookeepers.

Cutaneous and Mucocutaneous Leishmaniasis

Leishmaniasis is a chronic disease caused by flagellate protozoa of the genus Leishmania. It is a global disease, but most cases are seen in South America, the Mediterranean, and some areas of Asia and Africa. The 3 main types of leishmaniasis are cutaneous (the most common), mucocutaneous, and visceral (the most severe). Visceral leishmaniasis is also known as kala-azar. Leishmaniasis is diagnosed by demonstrating the presence of Leishmania amastigotes in clinical specimens using direct microscopic examination or molecular analysis. Various treatments exist, although the evidence supporting the options available for cutaneous leishmaniasis is weak. Both the classical presentation of leishmaniasis and our management of the disease have changed in recent decades because of acquired immune deficiency caused by conditions such as HIV infection or the use of TNF inhibitors.

The Leishmania donovani species complex: A new insight into taxonomy☆

Among the 20 or so Leishmania spp. described as pathogenic for humans, those of the Leishmania donovani complex are the exclusive causative agents of systemic and fatal visceral leishmaniasis. Although well studied, the complex is taxonomically controversial, which hampers clinical and epidemiological research. In this work, we analysed 56 Leishmania strains previously identified as L. donovani, Leishmania archibaldi or Leishmania infantum, isolated from humans, dogs and sandfly vectors throughout their distribution area. The strains were submitted to biochemical and genetic analyses and the resulting data were compared for congruence. Our results show: i) a partial concordance between biochemical and genetic-based data, ii) very limited genetic variability within the L. donovani complex, iii) footprints of frequent genetic exchange along an east-west gradient, marked by a widespread diffusion of alleles across the geographical range, and iv) a large-scale geographical spreading of a few genotypes. From a taxonomic point of view, considering the absence of relevant terminology in existing classes, the L. donovani complex could be treated as a single entity.