Increasing incidence of zoonotic visceral leishmaniasis on Crete, Greece

Leishmaniasis in Greece: Prospects of transitioning to a One Health surveillance system

Leishmaniasis is a high burden neglected disease in the Mediterranean ecoregion, lacking surveillance attention. We aimed to provide an overview of the state of leishmaniasis surveillance in Greece, investigating the prospect of transitioning to a One Health surveillance system. We conducted a narrative review describing human and animal leishmaniasis data from Greece, including entomological findings. Through a separate review process, we describe the current leishmaniasis surveillance system pertaining to humans, animals, vectors and the environment. Additionally, we distributed likert-scale questionnaires to key informants, capturing expert-view on the necessity, existing levels and barriers of OH leishmaniasis surveillance in Greece. We identified key system strengths, weaknesses, opportunities and threats respective to a OH transition through SWOT analysis. Greece is endemic for zoonotic visceral leishmaniasis (VL) and canine leishmaniasis (CanL), displaying an increasing VL trend in recent years and high national Leishmania seroprevalence rates in dogs (range: 13.8-23.4 %). Mandatory leishmaniasis notification in humans and animals, human case-based investigations, and active case finding activities in stray dogs, comprise valuable system components of high OH operational relevance. Conversely, the existing CanL surveillance governance and the lack of systematic entomological surveillance constitute important drawbacks. Moreover, the current context of public health and animal health financial constraints in Greece may impede a strategic OH transition in leishmaniasis surveillance. On the contrary, Greece's OH experience in West Nile Virus surveillance in conjunction with leishmaniasis-expert consensus on the necessity of OH surveillance and key barriers to its realization, compose important transition opportunities. Despite shortfalls in human, animal and vector surveillance, existing system characteristics, structures and practices comprise a promising basis for developing OH cross-sectoral leishmaniasis surveillance activities in Greece.

The potential impact of climate change on the seasonality of Phlebotomus neglectus, the vector of visceral leishmaniasis in the East Mediterranean region

Phlebotomus neglectus is one of the most important vectors of visceral leishmaniasis in Southeast Europe and Asia Minor. It was aimed to study the impact of climate change on the seasonality and the range of the species for 2014-2060. In the inland areas of Asia Minor, the Balkan Peninsula and the Carpathian Basin the elongation of the activity season will reach or exceed the two months in the middle of the 21st century compared to the end of the 20th century. The most affected regions are the middle elevations of the mountainous regions and the plains of the northern distribution areas. In some areas of the southern distribution border, the season is expected to shorten. In the Apennine Peninsula, mainly the mountainous areas could be impacted notably by climate change. The results indicate the potential spread of leishmaniasis in Southeast Europe due to the increasing environmental suitability of the region.

Sand fly synthetic sex-aggregation pheromone co-located with insecticide reduces the incidence of infection in the canine reservoir of visceral leishmaniasis: A stratified cluster randomised trial

OBJECTIVE

To evaluate the efficacy of a synthetic sex-aggregation pheromone of the sand fly vector Lu. longipalpis, co-located with residual insecticide, to reduce the infection incidence of Leishmania infantum in the canine reservoir.

METHODS

A stratified cluster randomised trial was designed to detect a 50% reduction in canine incident infection after 24 months in 42 recruited clusters, randomly assigned to one of three intervention arms (14 cluster each): synthetic pheromone + insecticide, insecticide-impregnated dog collars, or placebo control. Infection incidence was measured by seroconversion to anti-Leishmania serum antibody, Leishmania parasite detection and canine tissue parasite loads. Changes in relative Lu. longipalpis abundance within households were measured by setting three CDC light traps per household.

RESULTS

A total 1,454 seronegative dogs were followed-up for a median 15.2 (95% C.I.s: 14.6, 16.2) months per cluster. The pheromone + insecticide intervention provided 13% (95% C.I. 0%, 44.0%) protection against anti-Leishmania antibody seroconversion, 52% (95% C.I. 6.2%, 74·9%) against parasite infection, reduced tissue parasite loads by 53% (95% C.I. 5.4%, 76.7%), and reduced household female sand fly abundance by 49% (95% C.I. 8.2%, 71.3%). Variation in the efficacy against seroconversion varied between trial strata. Equivalent protection attributed to the impregnated-collars were 36% (95% C.I. 14.4%, 51.8%), 23% (95% C.I. 0%, 57·5%), 48% (95% C.I. 0%, 73.4%) and 43% (95% C.I. 0%, 67.9%), respectively. Comparison of the two interventions showed no statistically consistent differences in their efficacies; however, the errors were broad for all outcomes. Reductions in sand fly numbers were predominant where insecticide was located (chicken and dog sleeping sites), with no evidence of insecticide-induced repellence onto humans or dogs.

CONCLUSION

The synthetic pheromone co-located with insecticide provides protection particularly against canine L. infantum parasite transmission and sand fly vector abundance. The effect estimates are not dissimilar to those of the insecticide-impregnated collars, which are documented to reduce canine infection incidence, human infection and clinical VL disease incidence, in different global regions. The trialled novel lure-and-kill approach is a low-cost potential vector control tool against ZVL in the Americas.

Advances toward Diagnostic Tools for Managing Zoonotic Visceral Leishmaniasis

Visceral leishmaniasis (VL) is a life-threatening outcome of Leishmania infantum or Leishmania donovani infection. Dogs are the primary domestic reservoir of L. infantum parasites, and ownership of infected dogs increases the risk of human VL. Controlling infection within dog populations is regarded as critical to VL management in endemic countries, both preventing progression of canine disease and limiting parasite transmission to humans and dogs. Here we discuss various strategies that are used to diagnose canine visceral leishmaniasis (CVL) and the possibilities of adapting these for use within population screening and control programs. In addition, given the variable transmissibility of L. infantum to the sand fly vector, we outline some possibilities for the preferential identification of 'super-spreader' dogs among the overall infected population.

DNA sequencing confirms PCR-RFLP identification of wild caught Larroussius sand flies from Crete and Cyprus

Many Phlebotomine sand fly species (Diptera, Psychodidae) are vectors of the protozoan parasite Leishmania causing a group of diseases called the leishmaniases. The subgenus Larroussius includes sand fly vectors found in South East Mediterranean Basin responsible for Visceral (VL) and Cutaneous human leishmaniasis (CL). It is important to monitor these medically important insects in order to safely predict possible Leishmania transmission cycles. Leishmania infantum is endemic in the islands of Crete and Cyprus with increasing VL cases in humans and dogs and in Cyprus the newly introduced Leishmania donovani causes both VL and CL in humans. The morphological identification of the females of the subgenus Larroussius often presents difficulties. Morphology and COI PCR - RFLP were used to identify wild caught Larroussius sand flies belonging to Phlebotomus tobbi, P. perfiliewi, and P. neglectus species from Crete and Cyprus. The identification results were further confirmed by sequencing (DNA barcoding) and Bayesian phylogenetic analysis. COI PCR - RFLP, when correctly optimized and with respect to geographical origin, can serve as an initial patterning identification tool when large sand fly numbers need to be identified. It could accurately assign Larroussius females and males to their taxa overcoming the difficulties of morphological identification. Finally, DNA barcoding will contribute to a molecular identification database to be used for in-depth species studies.

Leishmania infantum and Dirofilaria immitis coinfection in dogs in Greece

Leishmaniasis and dirofilariasis are parasitic diseases of humans and dogs, worldwide, and they are often found as coinfections in endemic areas. Cases of human and canine dirofilariasis have being reported in Greece and leishmaniasis is endemic in most prefectures in humans and dogs. In most cases, dirofilariasis is established by parasitological (the modified Knott's test) and/or immunological methods, whilst for leishmaniasis molecular techniques and culture are also used. During an epidemiological study in Greece, 22·1% of the 5772 dogs studied were found positive by serology forLeishmania.Blood cultures of 165 (12·94%) of these animals producedLeishmaniapromastigotes and 26 (2·03%)Dirofilariamicrofilariae (L1), whilst only in two (0·16%) bothLeishmaniaandDirofilariaL1 appeared. The aim was to assess coinfections by the two parasites in dogs in Greece, the isolation and survival ofDirofilariamicrofilariae andLeishmaniapromastigotes using clotted blood (a fast, simple and low-cost method) and the survival potential of the two parasites in coexistence,in vitro.

Progress in the Mathematical Modelling of Visceral Leishmaniasis

The leishmaniases comprise a complex of diseases characterized by clinical outcomes that range from self-limiting to chronic, and disfiguring and stigmatizing to life threatening. Diagnostic methods, treatments, and vector and reservoir control options exist, but deciding the most effective interventions requires a quantitative understanding of the population level infection and disease dynamics. The effectiveness of any set of interventions has to be determined within the context of operational conditions, including economic and political commitment. Mathematical models are the best available tools for studying quantitative systems crossing disciplinary spheres (biology, medicine, economics) within environmental and societal constraints. In 2005, the World Health Assembly and government health ministers of India, Nepal, and Bangladesh signed a Memorandum of Understanding to eliminate the life threatening form of leishmaniasis, visceral leishmaniasis (VL), on the Indian subcontinent by 2015 through a combination of early case detection, improved treatments, and vector control. The elimination target is <1 case/10,000 population at the district or subdistrict level compared to the current 20/10,000 in the regions of highest transmission. Towards this goal, this chapter focuses on mathematical models of VL, and the biology driving those models, to enable realistic predictions of the best combination of interventions. Several key issues will be discussed which have affected previous modelling of VL and the direction future modelling may take. Current understanding of the natural history of disease, immunity (and loss of immunity), and stages of infection and their durations are considered particularly for humans, and also for dogs. Asymptomatic and clinical infection are discussed in the context of their relative roles in Leishmania transmission, as well as key components of the parasite-sandfly-vector interaction and intervention strategies including diagnosis, treatment and vector control. Gaps in current biological knowledge and potential avenues to improve model structures and mathematical predictions are identified. Underpinning the marriage between biology and mathematical modelling, the content of this chapter represents the first step towards developing the next generation of models for VL.

Geographical Distribution of MDR1 Expression in Leishmania Isolates, from Greece and Cyprus, Measured by the Rhodamine-123 Efflux Potential of the Isolates, Using Flow Cytometry

Leishmaniasis, a neglected vector-borne disease caused by the protozoan parasite Leishmania, is encountered in 98 countries causing serious concerns to public health. The most alarming is the development of parasite drug resistance, a phenomenon increasingly encountered in the field rendering chemotherapy ineffective. Although resistance to drugs is a complex phenomenon, the rate of efflux of the fluorescent dye Rhodamine-123 from the parasite body, using flow cytometry, is an indication of the isolate's ability to efflux the drug, thus avoiding death. The rate of efflux measured 275 Leishmania strains, isolated from patients and dogs from Greece and Cyprus, was measured and mapped to study the geographical distribution of the multidrug resistance (MDR) gene expression as an indication of the drug resistance of the parasite. The map showed that out of the seven prefectures, where dogs presented high efflux rates, five also had patients with high efflux rates. In one, out of the 59 prefectures studied, the highest number of isolates with efflux slope α > 1, in both human and dog isolates, was found; a fact which may suggest that spread of drug resistance is taking place. The virulence of the Leishmania strains, assessed after infecting human macrophages of the THP-1 cell line, fluctuated from 1% to 59.3% with only 2.5% of the isolates showing infectivity > 50%. The most virulent strains were isolated from Attica and Crete.

Current clinical, laboratory, and treatment outcome characteristics of visceral leishmaniasis: results from a seven-year retrospective study in Greece

OBJECTIVES

Visceral leishmaniasis (VL) is re-emerging in endemic areas. The epidemiological, clinical, laboratory, and treatment outcome characteristics in a large cohort of VL patients is described herein.

METHODS

The cases of 67 VL patients (57% male, mean age 56 years) treated in two Greek hospitals over the last 7 years were identified and evaluated retrospectively.

RESULTS

Forty-six percent of patients reported contact with animals. Seventeen patients (25%) were immunocompromised, and 22% were co-infected with another pathogen. Sixty-four percent of patients had fever, 57% had weakness, 37% had sweats, 21% had weight loss, and 13% had a dry cough, while 6% developed haemophagocytic syndrome. The median duration of symptoms was 28 days. Fifty-eight percent of patients had splenomegaly, 49% had hepatomegaly, and 36% had lymphadenopathy. The diagnosis was established by positive PCR in peripheral blood (73%) and/or bone marrow specimens (34%). Sixty-one patients (91%) received liposomal amphotericin (L-AMB). Six patients (10%) did not respond or relapsed but were eventually cured after a second cycle of L-AMB. During a 6-month follow-up, the overall mortality was 9%, although none of these deaths was attributed to VL.

CONCLUSIONS

VL is still a common disease in endemic areas, affecting immunocompetent and immunocompromised patients. Its diagnosis is challenging, and molecular techniques are valuable and helpful tools to achieve this. Treatment with L-AMB is safe and very effective.

The use of spatial analysis to estimate the prevalence of canine leishmaniasis in Greece and Cyprus to predict its future variation and relate it to human disease

Climatic, environmental, and demographic changes favor the emergence of neglected vector-borne diseases like leishmaniasis, which is spreading through dogs, the principle host of the protozoan Leishmania infantum. Surveillance of the disease in dogs is important, because the number of infected animals in an area determines the local risk of human infection. However, dog epidemiological studies are costly. Our aim was to evaluate the Emerging Diseases in a Changing European Environment (EDEN) veterinary questionnaire as a cost-effective tool in providing reliable, spatially explicit indicators of canine leishmaniasis prevalence. For this purpose, the data from the questionnaire were compared with data from two epidemiological studies on leishmaniasis carried out in Greece and Cyprus at the same time using statistical methods and spatial statistics. Although the questionnaire data cannot provide a quantitative measure of leishmaniasis in an area, it indicates the dynamic of the disease; information is obtained in a short period of time at low cost.

Genetic diversity and structure in Leishmania infantum populations from southeastern Europe revealed by microsatellite analysis

BACKGROUND

The dynamic re-emergence of visceral leishmaniasis (VL) in south Europe and the northward shift to Leishmania-free European countries are well-documented. However, the epidemiology of VL due to Leishmania infantum in southeastern (SE) Europe and the Balkans is inadequately examined. Herein, we aim to re-evaluate and compare the population structure of L. infantum in SE and southwestern (SW) Europe.

METHODS

Leishmania strains collected from humans and canines in Turkey, Cyprus, Bulgaria, Greece, Albania and Croatia, were characterized by the K26-PCR assay and multilocus enzyme electrophoresis (MLEE). Genetic diversity was assessed by multilocus microsatellite typing (MLMT) and MLM Types were analyzed by model- and distance- based algorithms to infer the population structure of 128 L. infantum strains.

RESULTS

L. infantum MON-1 was found predominant in SE Europe, whilst 16.8% of strains were MON-98. Distinct genetic populations revealed clear differentiation between SE and SW European strains. Interestingly, Cypriot canine isolates were genetically isolated and formed a monophyletic group, suggesting the constitution of a clonal MON-1 population circulating among dogs. In contrast, two highly heterogeneous populations enclosed all MON-1 and MON-98 strains from the other SE European countries. Structure sub-clustering, phylogenetic and Splitstree analysis also revealed two distinct Croatian subpopulations. A mosaic of evolutionary effects resulted in consecutive sub-structuring, which indicated substantial differentiation and gene flow among strains of both zymodemes.

CONCLUSIONS

This is the first population genetic study of L. infantum in SE Europe and the Balkans. Our findings demonstrate the differentiation between SE and SW European strains; revealing the partition of Croatian strains between these populations and the genetic isolation of Cypriot strains. This mirrors the geographic position of Croatia located in central Europe and the natural isolation of the island of Cyprus. We have analysed the largest number of MON-98 strains so far. Our results indicate extensive gene flow, recombination and no differentiation between MON-1 and MON-98 zymodemes. No correlation either to host specificity or place and year of strain isolation was identified. Our findings may be associated with intensive host migration and common eco-epidemiological characteristics in these countries and give valuable insight into the dynamics of VL.

Seroepidemiology of canine leishmaniosis in Évora (southern Portugal): 20-year trends

Background

Canine leishmaniosis (CanL) is an endemic zoonosis in the southern regions of Europe. This paper reports the trend in CanL seroprevalence in the municipality of Évora (southern Portugal), where the disease is endemic, over a period of 20 years. The work comprises three different studies that were conducted in the years of 1990 (n = 3,614), 1999 (n = 3,563) and 2010 (n = 1,485 dogs). Blood samples were collected during the anti-rabies vaccination campaigns. Anti-Leishmania antibodies were detected with the direct agglutination test (DAT).

Findings

The total percentages of DAT seropositive dogs were 3.9% (in 1990), 9.4% (in 1999) and 5.6% (in 2010). The overall seroprevalence was significantly higher in 1999 compared to 1990, but in 2010 a significant decrease was found in comparison with 1999. However, compared to 1990 the overall seroprevalence was still significantly higher in 2010. From 1990 to 2010 seroprevalence has switched from significantly lower to higher in the rural areas. Relatively few dogs showed clinical signs of overt disease (0.8% to 2.0%) with lymphadenopathy, onychogryphosis and skin involvement as most frequently observed. Gender associated differences in seroprevalence were not found, and most commonly seropositive dogs were working or stray animals. The mean age of seropositive dogs was significantly higher than seronegative dogs in all three sampling rounds.

Conclusions

A high proportion of dogs, which are apparently healthy, yet seropositive, may remain an important factor in limiting the outcome of zoonotic leishmaniosis control efforts.

Re-emergence of visceral and cutaneous leishmaniasis in the Greek Island of Crete

Leishmaniases are vector-borne diseases transmitted by phlebotomine sand flies. Three species of Leishmania are found in the Mediterranean basin: Leishmania infantum, the most common species responsible for both visceral (VL) and cutaneous leishmaniasis (CL); Leishmania major, found in North Africa and Middle East causing CL; Leishmania tropica with a limited presence in Europe, causing CL. During the last 25 years, Crete has become an endemic zone for L. infantum with a high number of infected dogs and an increasing number of human cases every year; in the last 4 years, the incidence has reached an average of seven VL patients per year in a population of 600,000. At the same time, CL has re-emerged in Crete due to L. tropica, with an average of three CL cases per year in the last 4 years. Isolates were typed as L. infantum MON-1 and MON-98 and L. tropica MON-300, a zymodeme not reported before. Both VL and CL have spread to the whole of the island during the last 25 years, primarily in semi-urban and urban areas with altitudes of 0-50 m. The prevailing Phlebotomus species were Phlebotomus neglectus (proven vector of L. infantum) and Phlebotomus similis (suspected vector of L. tropica).

Mapping the current distribution and predicted spread of the leishmaniosis sand fly vector in the madrid region (Spain) based on environmental variables and expected climate change

Leishmaniosis caused by Leishmania infantum is a widespread zoonotic disease that is endemic in the Mediterranean basin. Based on prior point abundance data for the two sand fly vectors of leishmaniosis in the Madrid region (Phlebotomus perniciosus and Phlebotomus ariasi), models were constructed to predict the spatial distribution patterns of these vectors. The models were obtained by negative binomial regression of several environmental variables and then used to map vector distributions. To validate the maps, we used serological prevalence data of Leishmania infection in dogs and incidence data were obtained through questionnaires completed by veterinarians in the region. Seropositive dogs and veterinary clinics registering a higher incidence of canine leishmaniosis appeared closer to our modeled vector foci. In the face of climate change, we simulated the future distributions of the sand flies for each third of the 21st century and predicted their spread in the region.

Transmission, reservoir hosts and control of zoonotic visceral leishmaniasis

Zoonotic visceral leishmaniasis (ZVL) caused by Leishmania infantum is an important disease of humans and dogs. Here we review aspects of the transmission and control of ZVL. Whilst there is clear evidence that ZVL is maintained by sandfly transmission, transmission may also occur by non-sandfly routes, such as congenital and sexual transmission. Dogs are the only confirmed primary reservoir of infection. Meta-analysis of dog studies confirms that infectiousness is higher in symptomatic infection; infectiousness is also higher in European than South American studies. A high prevalence of infection has been reported from an increasing number of domestic and wild mammals; updated host ranges are provided. The crab-eating fox Cerdocyon thous, opossums Didelphis spp., domestic cat Felis cattus, black rat Rattus rattus and humans can infect sandflies, but confirmation of these hosts as primary or secondary reservoirs requires further xenodiagnosis studies at the population level. Thus the putative sylvatic reservoir(s) of ZVL remains unknown. Review of intervention studies examining the effectiveness of current control methods highlights the lack of randomized controlled trials of both dog culling and residual insecticide spraying. Topical insecticides (deltamethrin-impregnated collars and pour-ons) have been shown to provide a high level of individual protection to treated dogs, but further community-level studies are needed.

A long-lasting topical deltamethrin treatment to protect dogs against visceral leishmaniasis

To develop long-lasting, topical pour-on insecticides for dogs to control zoonotic visceral leishmaniasis, two deltamethrin-based formulations (emulsifiable concentrate [EC] and suspension concentrate [SC]) were tested for their efficacy against the phlebotomine sandfly Lutzomyia longipalpis Lutz & Neiva (Diptera: Psychodidae), vector of Leishmania infantum Nicolle (Kinetoplastida: Trypanosomatidae). The entomological outcomes tested were anti-feeding effect (proportion of female sandflies unfed), lethal effect (24-h female sandfly mortality) and these two effects combined, and the insecticide persistence time at 50% (residual activity, RA50) and 80% (RA80) efficacy. On initial application, the proportions of female flies that demonstrated anti-feeding activity or were killed were similar for both formulations, at 0.93 (95% confidence interval [CI] 0.856-0.977) vs. 0.81 (95% CI 0.763-0.858) (anti-feeding) and 0.86 (95% CI 0.787-0.920) vs. 0.76 (95% CI 0.698-0.817) (24-h mortality) for EC and SC, respectively. The RA(50) rates for anti-feeding and mortality caused by the EC formulation were 4.7 months (95% CI 4.18-5.84) and 2.5 months (95% CI 2.25-2.90), respectively, compared with 1.1 months (95% CI 0.96-1.15) and 0.6 months (95% CI 0.50-0.61), respectively, for the SC formulation. The RA(50) for the combined anti-feeding and mortality effects of EC was 5.2 months (95% CI 4.73-5.96), compared with only 0.9 months (95% CI 0.85-1.00) for the SC formulation. The four- to six-fold superior residual activity of the EC formulation was attributed to the addition of a solvent-soluble resin in the formulation which improved fur adhesion and acted as a reservoir for the slow release of the active ingredient. These results identify the potential of such a low-cost formulation to reduce the inter-intervention interval to 5-6 months, similar to that recommended for deltamethrin-impregnated dog collars or for re-impregnation of conventional bednets, both of which are currently used to combat Leishmania transmission. Finally, a novel bioassay was developed in which sandflies were exposed to fur from treated dogs, revealing no detectable tolerance (24-h mortality) in wild-caught sandflies to the insecticide formulations up to 8 months after the initiation of communitywide application of the insecticides to dogs.