Application of molecular techniques in the study of natural infection of Leishmania infantum vectors and utility of sandfly blood meal digestion for epidemiological surveys of leishmaniasis

Fauna and seasonality of sand flies (Diptera: Psychodidae: Phlebotominae) from a leishmaniasis transmission area in the central region of Rio Grande do Sul, Brazil

Sand flies, vectors capable of transmitting Leishmania spp. and causing leishmaniasis, have been a concern in the central region of Rio Grande do Sul, where canine leishmaniasis (CanL) has been documented since 1985. Notably, there has been a surge in CanL cases since 2017, with two autochthonous cases of human visceral leishmaniasis reported in the area in 2021. This study aimed to identify the sand fly fauna potentially involved in disease transmission. Modified Centers for Disease Control light traps were deployed in three neighborhoods of the city where CanL cases had been previously reported, spanning January 2021 to December 2022. Of the 89 collections conducted, 119 sand flies belonging to five species were captured: Pintomyia fischeri (76/119, 63.86%), Migonemyia migonei (23/119, 19.33%), Lutzomyia longipalpis (16/119, 13.45%), Brumptomyia sp. (2/119, 1.68%), and Psathyromyia lanei (2/119, 1.68%), predominantly between February and April in 2021 and 2022. Polymerase chain reaction testing on all female specimens yielded negative results for Leishmania spp. DNA. Although Leishmania spp. was not detected in these vectors, these findings underscore the imperative to implement measures aimed at curtailing the proliferation of these insects.

The estimated distribution of autochthonous leishmaniasis by Leishmania infantum in Europe in 2005-2020

BACKGROUND

This study describes the spatial and temporal distribution between 2005 and 2020 of human and animal leishmaniasis by Leishmania infantum in European countries reporting autochthonous cases, and highlights potential activities to improve disease control.

METHODOLOGY/PRINCIPAL FINDINGS

It was based on a review of the scientific literature and data reported by the World Health Organization (WHO), the World Organization for Animal Health (WOAH) and the Ministries of Health, including hospital discharges in some countries. Autochthonous infections were reported in the scientific literature from 22 countries, including 13 and 21 countries reporting human and animal infections, respectively. In contrast, only 17 countries reported autochthonous human leishmaniasis cases to the WHO and 8 countries animal infections to the WOAH. The number of WOAH reported cases were 4,203, comprising 4,183 canine cases and 20 cases in wildlife. Of 8,367 WHO reported human cases, 69% were visceral leishmaniasis cases-of which 94% were autochthonous-and 31% cutaneous leishmaniasis cases-of which 53% were imported and mostly in France. The resulting cumulative incidence per 100,000 population of visceral leishmaniasis between 2005-2020, was highest in Albania (2.15 cases), followed by Montenegro, Malta, Greece, Spain and North Macedonia (0.53-0.42), Italy (0.16), Portugal (0.09) and lower in other endemic countries (0.07-0.002). However, according to hospital discharges, the estimated human leishmaniasis incidence was 0.70 in Italy and visceral leishmaniasis incidences were 0.67 in Spain and 0.41 in Portugal.

CONCLUSIONS/SIGNIFICANCE

Overall, there was no evidence of widespread increased incidence of autochthonous human leishmaniasis by L. infantum in European countries. Visceral leishmaniasis incidence followed a decreasing trend in Albania, Italy and Portugal, and peaked in Greece in 2013, 2014 and 2017, and in Spain in 2006-2007 and 2011-2013. Animal and human cutaneous leishmaniasis remain highly underreported. In humans, hospital discharge databases provide the most accurate information on visceral leishmaniasis and may be a valuable indirect source of information to identify hotspots of animal leishmaniasis. Integrated leishmaniasis surveillance and reporting following the One Health approach, needs to be enhanced in order to improve disease control.

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.

Molecular detection of Leishmania infantum DNA and host blood meal identification in Phlebotomus in a hypoendemic focus of human leishmaniasis in northern Algeria

BACKGROUND

Leishmania parasites are transmitted by female phlebotomine sand flies that maintain the enzootic cycle by circulating between sylvatic and domestic mammals. Humans are part of this cycle as accidental hosts due to the vector's search for a source of blood. In Algeria, Human Leishmaniases (HL) are endemic and represent a serious public health problem because of their high annual incidence and their spread across the country. The aim of this study is to identify sand fly species fauna (vectors of Leishmania), determine their infection rate and identify their feeding preferences using molecular tools in a hypoendemic focus of HL located in the province of Tipaza, northern Algeria.

METHODOLOGY/PRINCIPAL FINDINGS

An entomological survey using CDC light traps was conducted between July and October of 2015 in four HL affected peri-urban locations in the province of Tipaza, northern Algeria. Sand flies were identified using the morphological criteria of the genitalia for the males and spermathecae for the females. Leishmania DNA was detected in pooled female sand flies (N = 81 pools with 8-10 specimens per pool) using quantitative real-time polymerase chain reaction (qPCR) targeting two different genes: kDNA-PCR and 18S rRNA. To identify their blood meal sources, blood-fed female sand flies were analyzed by PCR-sequencing targeting the vertebrate cytochrome c oxidase I (COI) gene. A total of 4,045 sand flies were caught, of which 3,727 specimens were morphologically identified. Seven species were recorded: P. (L.) perniciosus (50.28%), P. (L.) perfiliewi (26.13%), P. (L.) longicuspis (21.92%), Sergentomyia (S.) minuta (0.85%), P. (P.) papatasi (0.42%), P. (L.) langeroni (0.32%) and P. (L.) ariasi (0.05%). Afterwards, 740 female specimens were randomly selected and divided into 81 pools and were then screened to investigate the presence of Leishmania spp. L. infantum DNA was detected in three pools, corresponding to three sand fly specimens (one each). The infection rate was 0.33% (2/600) for P. (L.) perniciosus and 2.56% (1/39) for P. (L.) perfiliewi. Analysis of the blood feeding sources (N = 88 specimens) revealed that sand flies belonging to Larroussius subgenera, mainly (71.5%) feed on small ruminants. Human blood is the second feeding source (17%), eight specimens (9%) were found to feed on equines and no domestic reservoir (dog) blood was found.

CONCLUSIONS/SIGNIFICANCE

The presence of human leishmaniasis cases, the high abundance of Phlebotomus (Larroussius) species which are proven or suspected vectors of L. infantum, and the detection of L. infantum DNA from its natural vectors (P. (L.) perniciosus, P. (L.) perfiliewi), in addition to the blood-feeding of positive females for L. infantum on humans blood, prove that the major elements of the epidemiological transmission cycle of L. infantum are present and indicate risk factors for an outbreak of the disease in the province of Tipaza.

Isoenzymatic characterization of Phlebotomus ariasi and P. perniciosus of canine leishmaniasis foci from Eastern Pyrenean regions and comparison with other populations from Europe

An entomological survey was carried out in 2007 in two Pyrenean counties of Lleida province (north-eastern Spain), where cases of autochthonous canine leishmaniasis have been recently reported. Phlebotomus ariasi and P. perniciosus, vectors of Leishmania infantum in the Mediterranean area, were captured. The aim of the present study was to compare these phlebotomine populations with others captured in known leishmaniasis foci in Europe. Populations of these species were studied by analysing the polymorphism of seven enzymatic systems (HK, PGI, PGM, MDH, 6PGD, FUM and ACO) and compared with other specimens from endemic regions of France, Italy, Malta, Portugal and Spain captured in other campaigns, and also with previously published results. Phlebotomusariasi was more polymorphic than P. perniciosus. Only the ACO locus had diagnostic alleles, but some other alleles show high characteristic frequencies for each species. The neighbour-joining trees separated two population groups in both species. On the basis of the isoenzyme study results, sand fly populations of the Pyrenean region in Lleida province are closely related to those of other nearby leishmaniasis endemic regions in France and Spain.

The current status of phlebotomine sand flies in Albania and incrimination of Phlebotomus neglectus (Diptera, Psychodidae) as the main vector of Leishmania infantum

The incidence of visceral leishmaniasis (VL) in Albania is higher than in other countries of southern Europe, however the role of local sand fly species in the transmission of Leishmania infantum was not addressed conclusively. In 2006, a country-wide collection of sand flies performed in 14 sites selected based on recent occurrence of VL cases showed that Phlebotomus neglectus was by far the most prevalent species (95.6%). Furthermore, 15% of pools made from 422 P. neglectus females tested positive for Leishmania sp. genomic DNA. In the same year, Culicoides trapping was performed for bluetongue disease surveillance in 91 sites of southern Albania, targeting livestock farms regardless recent occurrence of VL in the surveyed areas. In 35 sites where sand flies were collected along with midges, Phlebotomus perfiliewi was the most prevalent among the Phlebotomus species identified, however search for leishmanial DNA in females of this species was unsuccessful. In 2011, sand flies were trapped in 4 sites of north Albania characterized by high VL incidence, and females were dissected to search for Leishmania infections. Both P. neglectus and P. tobbi were collected at high densities. Two positive specimens were detected from a sample of 64 P. neglectus trapped in one site (3.1%). Parasites were successfully cultured from one specimen and characterized as belonging to Leishmania infantum zymodeme MON-1, the only zymodeme so far identified as the agent of human and canine leishmaniasis in the country. Altogether our studies indicate that P. neglectus is the main leishmaniasis vector in Albania.

Detection of Leishmania DNA and blood meal sources in phlebotomine sand flies (Diptera: Psychodidae) in western of Spain: Update on distribution and risk factors associated

Leishmaniosis caused by Leishmania infantum is present in Mediterranean countries, with high prevalence in areas of the center and south of Spain. However, in some regions such as Extremadura (in southwest of Spain), data has not been updated since 1997. The aim of this work was (i) to provide information about the distribution of phlebotomine sand fly species in western of Spain (Extremadura region), (ii) to determine risk factors for the presence of sand fly vectors and (iii) to detect Leishmania DNA and identify blood meal sources in wild caught females. During 2012-2013, sand flies were surveyed using CDC miniature light-traps in 13 of 20 counties in Extremadura. Specimens were identified morphologically and females were used for molecular detection of Leishmania DNA by kDNA, ITS-1 and cyt-B. In addition, blood meals origins were analyzed by a PCR based in vertebrate cyt b gene. A total of 1083 sand flies of both gender were captured and identified. Five species were collected, Phlebotomus perniciosus (60.76%), Sergentomyia minuta (29.92%), P. ariasi (7.11%), P. papatasi (1.48%) and P. sergenti (0.74%). The last three species constitute the first report in Badajoz, the most southern province of Extremadura region. Leishmania DNA was detected in three out of 435 females (one P. pernicious and two S. minuta). Characterization of obtained DNA sequences by phylogenetic analyses revealed close relatedness with Leishmania tarentolae in S. minuta and L. infantum in P. perniciosus. Haematic preferences showed a wide range of hosts, namely: swine, humans, sheep, rabbits, horses, donkeys and turkeys. The simultaneous presence of P. perniciosus and P. ariasi vectors, the analysis of blood meals, together with the detection of L. infantum and in S. minuta of L. tarentolae, confirms the ideal conditions for the transmission of this parasitosis in the western of Spain. These results improve the epidemiological knowledge of leishmaniosis and its vectors in this part of Spain, highlighting the need for ongoing entomological and parasitological surveillance.

Sampling strategies for phlebotomine sand flies (Diptera: Psychodidae) in Europe

The distribution of phlebotomine sand flies is widely reported to be changing in Europe. This can be attributed to either the discovery of sand flies in areas where they were previously overlooked (generally following an outbreak of leishmaniasis or other sand fly-related disease) or to true expansion of their range as a result of climatic or environmental changes. Routine surveillance for phlebotomines in Europe is localized, and often one of the challenges for entomologists working in non-leishmaniasis endemic countries is the lack of knowledge on how to conduct, plan and execute sampling for phlebotomines, or how to adapt on-going sampling strategies for other haematophagous diptera. This review brings together published and unpublished expert knowledge on sampling strategies for European phlebotomines of public health concern in order to provide practical advice on: how to conduct surveys; the collection and interpretation of field data; suitable techniques for the preservation of specimens obtained by different sampling methods; molecular techniques used for species identification; and the pathogens associated with sand flies and their detection methods.

Detection of Leishmania infantum and identification of blood meals in Phlebotomus perniciosus from a focus of human leishmaniasis in Madrid, Spain

Since 2010, the number of cases of both human visceral leishmaniasis and cutaneous leishmaniasis in southwestern Madrid region (Spain) and more specifically in the town of Fuenlabrada has increased. Direct xenodiagnosis of leishmaniasis proved that hares (Lepus granatensis) from this focus are able to infect with Leishmania infantum colonized Phlebotomus perniciosus. To a better understanding of this focus of leishmaniasis, we conducted an entomological survey using CDC light traps, at the end of the seasonal transmission period of 2011 before the beginning of control measures of the disease, to study the phlebotomine sand flies species involved. Detection of Leishmania DNA in the sand flies captured was studied by kDNA-PCR and cpb-PCR. In addition, blood fed and gravid female P. perniciosus were analysed by a PCR based in vertebrate cytochrome b (cyt b) gene. Taxonomic identification of captured sand flies (n = 174) as P. perniciosus (n = 171) and Sergentomyia minuta (n = 3) together with the analysis of blood feeding in ten sand flies that shows a high preference for hares (n = 6), followed by humans (n = 3), and cats (n = 1) confirm a strong association between P. perniciosus hares and humans in the focus. Moreover, 79 out of 135 (58.5 %) P. perniciosus were positive to L. infantum by PCR approaches. These data support the increase of human leishmaniasis cases in the area and the existence of an unusual sylvatic cycle alternative to the classical domestic one, where the dog is the main reservoir of L. infantum.

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.

First survey on canine leishmaniasis in a non classical area of the disease in Spain (Lleida, Catalonia) based on a veterinary questionnaire and a cross-sectional study

The Spanish distribution of canine leishmaniasis (CanL) is heterogeneous and very few data are available for the north of the country, including the province of Lleida (Catalonia, Spain). This work describes the results obtained from a questionnaire sent to veterinarians throughout the province of Lleida. The majority of veterinarians (25/32, 78.1%) believed CanL cases were increasing and that the dogs had been infected locally (30/32, 93.8%). Also, a cross-sectional study was performed on the seroprevalence of CanL in kennel dogs, with and without compatible clinical signs, in the county of Pallars Sobirà (Pyrenees of Lleida), where an autochthonous case of CanL had been previously detected. Four serological tests were used (IFAT, ELISA, Western blot, ICF) and dogs that tested positive with at least two immunological methods were considered seropositive and probably infected. 33.1% (48/145) of the dogs were seropositive. The results of a mixed logistic regression model showed that the risk of seropositivity increased with age (OR=1.35, p-value=0.002), among dogs living in the southern part of Pallars Sobirà (OR=6.20, p-value=0.025) and among dogs whose owners considered their animals to be at risk of leishmaniasis infection (OR=1.26, p-value=0.024) and who were unaware of anti-sand fly preventive methods (OR=11.6, p-value=0.009). The risk decreased when dogs lived in an urban-periurban habitat (OR=0.17, p-value=0.002). The information gathered in the veterinary questionnaires helped us to define the knowledge, perception and awareness of the disease in a naïve region, supporting the hypothesis of an existing CanL focus in Pallars Sobirà, which was confirmed by the seroepidemiological survey. The seroprevalence study carried out on kennel dogs of local origin proved useful for detecting an autochthonous focus of leishmaniasis through the analysis of a small number of animals.