Variations in seroprevalences of canine leishmaniasis: Could it be a consequence of the population structure?

Exploring the impact of epidemiological and clinical factors on the progression of canine leishmaniosis by statistical and whole genome analyses: from breed predisposition to comorbidities

Canine leishmaniosis (CanL), caused by Leishmania infantum, is a complex disease of growing importance in Europe. Clinical manifestations result from the down-modulation of the host immune response through multiple host-parasite interactions. Although several factors might influence CanL progression, this is the first known study evaluating risk factors for its different clinical stages in a large referral hospital population (n = 35.669) from an endemic area, over a 20 year period. Genome-wide scans for selection signatures were also conducted to explore the genomic component of clinical susceptibility to L. infantum infection. The prevalence of CanL was 3.2% (16.7% stage I; 43.6% stage II; 32.1% stage III; 7.6% stage IV). Dog breed (crossbreed), bodyweight (<10 kg), living conditions (indoors), regular deworming treatment, and being vaccinated against Leishmania significantly decreased the transmission risk and the risk for developing severe clinical forms. Conversely, the detection of comorbidities was associated with advanced clinical forms, particularly chronic kidney disease, neoplasia, cryptorchidism, infectious tracheobronchitis and urate urolithiasis, although those did not impact the clinical outcome. Significant associations between an increased risk of severe clinical stages and findings in the anamnesis (renal or skin-related manifestations) and physical examination (ocular findings) were also detected, highlighting their diagnostic value in referred cases of CanL. Sixteen breeds were found to be significantly more susceptible to developing severe stages of leishmaniosis (e.g. Great Dane, Rottweiler, English Springer Spaniel, Boxer, American Staffordshire Terrier, Golden Retriever), while 20 breeds displayed a clinical resistantance phenotype and, thus, are more likely to mount an efficient immune response against L. infantum (e.g. Pointer, Samoyed, Spanish Mastiff, Spanish Greyhound, English Setter, Siberian Husky). Genomic analyses of these breeds retrieved 12 regions under selection, 63 candidate genes and pinpointed multiple biological pathways such as the IRE1 branch of the unfolded protein response, which could play a critical role in clinical susceptibility to L. infantum infection.

Leishmania infantum infection serosurveillance in stray dogs inhabiting the Madrid community: 2007-2018

Background

Leishmaniosis is an endemic zoonotic disease in the Mediterranean basin caused by Leishmania infantum and transmitted by phlebotomine sandflies. While in dogs disease may be severe, leishmaniosis is also a public health concern as was shown in the largest outbreak of human leishmaniosis (HL) in Europe in 2009 occurring in the Madrid region. The aim of the present study was to assess the applicability of the Leishmaniosis Surveillance Program (LeishSP) established in Madrid in 1996 by examining trends in L. infantum seroprevalence and associated epidemiological risk factors based on data for the 2007–2018 period.

Methods

The study population consisted of 3225 stray dogs from 17 animal shelters collaborating with the LeishSP. Seroprevalences were recorded twice annually (April and November) from 2007 to 2018. In each yearly period, a minimum of 100 dogs were tested to detect dogs infected before and after the sandfly risk season in Madrid area. Each dog was subjected to the same protocol of blood sample collection and clinical examination to collect epidemiological data and clinical signs. Anti-Leishmania-specific IgG was determined by IFAT cut-off ≥ 1:100.

Results

Overall seroprevalence was 6.1% (198 positive dogs). Epidemiological data indicate a significantly higher seroprevalence in dogs > 4 years old, purebred dogs (Pit Bull and related breeds), and medium to large size dogs. There were no seroprevalence differences according to sex and/or season (April and November). In addition, no significant differences were observed according to whether dogs lived inside or outside the HL outbreak area. Remarkably, of 198 dogs testing positive for L. infantum, 64.6% had no clinical signs, indicating a high proportion of clinically healthy infected dogs that could be a potential source of infection.

Conclusions

Results indicate a stable seroprevalence of L. infantum infection after 2006 in stray dogs in Madrid but with a recent slightly increasing trend. These observations support the need to continue with the LeishSP implemented by sanitary authorities of the Madrid Community as an early warning strategy for human and animal leishmaniosis and to enable continued assessment of the epidemiological role of dogs with subclinical infection in this important zoonotic disease.

Graphical Abstract

Latest trends in Leishmania infantum infection in dogs in Spain, Part I: mapped seroprevalence and sand fly distributions

Background

This report describes L. infantum infection seroprevalence in dogs in Spain through data obtained from peer-reviewed literature and a cross-sectional serological survey assessing epidemiological and habitat variables as risk factors for infection. The study also provides preliminary sand fly species distribution data and indicates factors affecting their distribution and density.

Methods

Three different studies were conducted in Spain: (i) a peer-reviewed literature seroprevalence survey (1985–2019); (ii) a cross-sectional serological survey (2011–2016); and (iii) a preliminary entomological survey (2013–2014). In the cross-sectional serological survey, 1739 dogs from 74 different locations including 25 Spanish provinces were tested for L. infantum by indirect immunofluorescence antibody test (IFAT) (antibody titre ≥ 1:100). Seroprevalence of L. infantum infection was analysed by province and bioclimatic zone. Statistics were used to analyse relationships between several dog- and environment-related variables and L. infantum seroprevalence. In parallel, during 2013–2014, sand flies were collected across the Iberian Peninsula and the Balearic Islands using CDC light traps to examine relationships between habitat-related factors and sand fly species densities (number of sand flies per trap per hour).

Results

The literature review revealed that the provinces showing the highest seroprevalence were Balearic Islands (57.1%), Ourense (35.6%), Málaga (34.6%) and Cáceres (34.2%), and those showing the lowest seroprevalence were Vizcaya (0%), Cantabria (2.0%) and Álava (3.3%). In our survey, anti-Leishmania IgG antibodies were detected in 176 of the 1739 dogs rendering a seroprevalence of 10.12%. Percentage seroprevalence distributions significantly varied among bioclimatic belts. Seropositivity for L. infantum was related to size (large breed dogs versus small) and were significantly higher in younger dogs (≤ 1 years-old). In the entomological survey, 676 sand flies of five species were captured: 562 (83.13%) Phlebotomus perniciosus; 64 (9.47%) Sergentomyia minuta; 38 (5.62%) P. ariasi: 6 (0.89%) P. sergenti; and 6 (0.89%) P. papatasi. Phlebotomus perniciosus showed a greater density in the thermo-Mediterranean than in the meso-Mediterranean zone. Densities of S. minuta and P. ariasi were significantly higher in rural habitats.

Conclusions

This updated seroprevalence map of L. infantum infection in dogs in Spain defines non-endemic, hypoendemic, endemic and hyperendemic areas, and confirms P. perniciosus as the most abundant sand fly vector in Spain.

Evaluation of various biomarkers for kidney monitoring during canine leishmaniosis treatment

Background

The objective of this study was to evaluate and compare the evolution of the profile currently recommended by the International Renal Interest Society (IRIS) (sCr, UPC and sSDMA) with a panel of other different kidney biomarkers during treatment for canine leishmaniosis. This panel included three urinary glomerular biomarkers (uIgG, uCRP and uferritin) and three urinary tubular biomarkers (uGGT, uNAG and uRBP).

These biomarkers were measured in two groups of dogs with canine leishmaniosis at IRIS stage I. Group 1: dogs showing proteinuria (UPC > 0.5) before treatment which did not decrease after treatment; Group 2: dogs showing proteinuria before treatment which decreased after treatment.

Results

Group 1 showed no significant changes in any biomarker after treatment. In group 2, among the biomarkers recommended by the IRIS, only UPC showed a significant decrease after treatment. However all biomarkers of glomerular damage showed a significant decrease after treatment, with uIgG/Cr and uCRP/Cr showing the greater decreases. In addition uRBP/Cr and uNAG/Cr showed significant decreases after treatment.

Conclusions

In dogs with leishmaniosis at IRIS stage I that reduced UPC after treatment, there were no significant changes in serum creatinine and sSDMA. However, all the urine biomarkers evaluated with exception of uGGT showed a significant decrease. These decreases were more evident in those markers related with glomerular function, being uIgG/Cr the biomarker more associated with UPC. Further studies involving a larger number of animals and histological analysis of the kidney would be recommended to confirm these findings and evaluate the routine practical use of these urine biomarkers in canine leishmaniosis.