Regional parasite density in the skin of dogs with symptomatic canine leishmaniosis

Serum cobalamin concentrations in dogs with leishmaniosis before and during treatment

Hypocobalaminemia in dogs is most commonly associated with gastrointestinal disorders leading to impaired absorption and utilization of cobalamin. The objectives of this study were to compare serum cobalamin concentrations between dogs with leishmaniosis and clinically healthy dogs, and to assess possible alterations of serum cobalamin concentrations in dogs with leishmaniosis at different timepoints during treatment. Fifty-five dogs with leishmaniosis and 129 clinically healthy dogs were prospectively enrolled. Diagnosis of leishmaniosis was based on clinical presentation, positive serology and microscopic detection of Leishmania amastigotes in lymph node aspiration smears. Twenty of the dogs with leishmaniosis were treated with a combination of meglumine antimonate and allopurinol for 28 days and serum cobalamin concentrations were measured in blood samples that were collected before initiation of treatment (timepoint 0) and on days 14 and 28. In order to estimate alterations of serum cobalamin concentrations during treatment, cobalamin concentrations were measured in blood samples from 20 out of 55 dogs with leishmaniosis at all timepoints. Serum cobalamin concentrations were significantly lower in dogs with leishmaniosis before treatment (median: 362 ng/L; IQR: 277-477 ng/L) compared to clinically healthy dogs (median: 470 ng/L; IQR: 367-632 ng/L; P = 0.0035). Serum cobalamin concentrations increased significantly in dogs with leishmaniosis on day 14 of treatment compared to timepoint 0 (P = 0.02). In the present study, serum cobalamin concentrations were significantly lower in dogs with leishmaniosis compared to clinically healthy dogs. In addition, there was an increase in serum cobalamin concentrations during treatment. The clinical significance of hypocobalaminemia in dogs with leishmaniosis remains to be determined.

Serological tests fail to discriminate dogs with visceral leishmaniasis that transmit Leishmania infantum to the vector Lutzomyia longipalpis

INTRODUCTION

The control of reservoirs for Leishmania infantum -induced zoonotic visceral leishmaniasis requires the identification of dogs posing a population risk. Here, we assessed the performance of several assays to identify Lutzomyia longipalpis infectious dogs.

METHODS

We evaluated 99 dogs that were positive for visceral leishmaniasis based on parasite identification. Serological analyses were performed using an enzyme-linked immunosorbent assay, immunofluorescence antibody tests in 1:40 and 1:80 dilutions, rapid dual path platform tests, immunochromatographic assay with a recombinant rK39 antigen, fast agglutination screening tests, and direct agglutination tests. We also performed PCR to analyze peripheral blood and xenodiagnosis.

RESULTS

Forty-six dogs infected at least one L. longipalpis specimen. Although the serological test sensitivities were above 85% for detecting L. longipalpis infectious dogs, none showed a satisfactory performance, as both specificity (0.06 to 13%) and the area under the receiver operating characteristic curve (45 to 53%) were low. The PCR results were also weak, with a sensitivity of 30%, specificity of 72%, and an area under the receiver operating characteristic curve of 51%. The infected L. longipalpis proportion was higher among asymptomatic dogs than symptomatic dogs. Among the symptomatic dogs, those with ulceration-free skin diseases were more infectious, with an odds ratio of 9.3 (confidence interval of 1.10 - 428.5). The larger the number of insects fed, the greater the detected infectiousness.

CONCLUSIONS

Our study supports the imperative to develop novel technologies for identifying the infectious dogs that transmit L. infantum for the benefit of public health.

In situ CUTANEOUS CELLULAR IMMUNE RESPONSE IN DOGS NATURALLY AFFECTED BY VISCERAL LEISHMANIASIS

Thirty-eight dogs naturally affected by visceral leishmaniasis were recruited in Araçatuba, São Paulo State, Brazil - an endemic area for visceral leishmaniasis. The animals were distributed into one of two groups, according to their clinical and laboratory features, as either symptomatic or asymptomatic dogs. Correlations between clinical features and inflammatory patterns, cellular immune responses, and parasitism in the macroscopically uninjured skin of the ear were investigated. Histological skin patterns were similar in both groups, and were generally characterized by a mild to intense inflammatory infiltrate in the dermis, mainly consisting of mononuclear cells. There was no difference in the number of parasites in the skin (amastigotes/mm²) between the two groups. Concerning the characterization of the cellular immune response, the number of positive inducible nitric oxide synthase (iNOS⁺⁾ cells was higher in the dermis of symptomatic than in asymptomatic dogs (p = 0.0368). A positive correlation between parasite density and macrophages density (p = 0.031), CD4⁺ T-cells (p = 0.015), and CD8⁺ T-cells (p = 0.023) was observed. Furthermore, a positive correlation between density of iNOS⁺ cells and CD3⁺ T-cells (p = 0.005), CD4⁺ T-cells (p = 0.001), and CD8⁺ T-cells (p = 0.0001) was also found. The results showed the existence of a non-specific chronic inflammatory infiltrate in the dermis of dogs affected by visceral leishmaniasis, characterized by the presence of activated macrophages and T-lymphocytes, associated to cutaneous parasitism, independent of clinical status.

Comparison of optical microscopy and quantitative polymerase chain reaction for estimating parasitaemia in patients with kala-azar and modelling infectiousness to the vector Lutzomyia longipalpis

Currently, the only method for identifying infective hosts with Leishmania infantum to the vector Lutzomyia longipalpis is xenodiagnosis. More recently, quantitative polymerase chain reaction (qPCR) has been used to model human reservoir competence by assuming that detection of parasite DNA indicates the presence of viable parasites for infecting vectors. Since this assumption has not been proven, this study aimed to verify this hypothesis. The concentration of amastigotes in the peripheral blood of 30 patients with kala-azar was microscopically verified by leukoconcentration and was compared to qPCR estimates. Parasites were identified in 4.8 mL of peripheral blood from 67% of the patients, at a very low concentration (average 0.3 parasites/mL). However, qPCR showed 93% sensitivity and the estimated parasitaemia was over a thousand times greater, both in blood and plasma, with higher levels in plasma than in blood. Furthermore, the microscopic count of circulating parasites and the qPCR parasitaemia estimates were not mathematically compatible with the published proportions of infected sandflies in xenodiagnostic studies. These findings suggest that qPCR does not measure the concentration of circulating parasites, but rather measures DNA from other sites, and that blood might not be the main source of infection for vectors.

Parasite load in intact and ulcerative skin of dogs with leishmaniais

The skin is the site of inoculation of Leishmania spp. in susceptible hosts, and consequently dermatopathies, especially ulcerative dermatitis, are the main clinical signs observed. The aim of this study was to assess parasitism of the skin (intact and ulcerated) among dogs that were naturally infected by Leishmania spp., through immunohistochemical analysis. Skin fragments (intact and ulcerated) were collected from 13 dogs with positive parasitological (bone marrow aspiration and exfoliative skin) and serological examinations (ELISA S7 Biogene) for Leishmania spp. These samples were processed using the immunohistochemical technique, involving the streptavidin-peroxidase complex. Ulcerative lesions were mainly observed on the elbows (53.84%; 7/13), nostrils (15.38%; 2/13), ears (23.07%; 3/13) and wings of the ilium (7.69%; 1/13). A severe parasite load was detected in 46.15% and 76.92% of the intact and ulcerated skin samples tested, respectively. The parasite load on ulcerated skin was statistically higher than on intact skin (p = 0.0221). These results indicate that the intact and ulcerated skin may host a high parasite load of amastigote forms of Leishmania spp., which can favor the transmission of the parasite.

An update on the diagnosis and treatment of canine leishmaniosis caused by Leishmania infantum (syn. L. chagasi)

Canine leishmaniosis caused by Leishmania infantum is still a common disease in endemic areas, such as the Mediterranean countries, and has progressively expanded into non-endemic areas like Central and Northern Europe. The aim of this article is to critically review current knowledge on the diagnosis and treatment of this disease. In dogs with typical clinical signs and clinicopathological abnormalities, diagnosis is relatively easy based on the exclusion of major differentials, the demonstration of the parasite (e.g., with lymph node and/or skin cytology) and the presence of Leishmania-specific immunoglobulin G antibodies (quantitative serology). In less typical cases, these criteria together with the exclusion of possible differentials and the demonstration of compatible histological lesions in affected organs and tissues form the basis for a sound diagnosis. In clinically healthy dogs, molecular techniques are the most sensitive means for detecting L. infantum infection. Treatment of canine leishmaniosis should follow clinical staging and is usually based on meglumine antimonate or miltefosine administration for a few weeks in combination with allopurinol for several months. However, allopurinol monotherapy may be used in very mild cases as well as in dogs with end stage kidney disease. Aminosidine administered once daily at a revised dosage shows some promise but additional controlled studies are needed. Close attention to published guidelines regarding treatment and follow-up is necessary to achieve the best possible therapeutic outcome.

Pathologic mechanisms underlying the clinical findings in canine leishmaniasis due to Leishmania infantum/chagasi

In dogs with symptomatic or asymptomatic leishmaniasis, Leishmania infantum appears to induce a mixed Th1/Th2 immune response that in the sick dog may eventually result in tissue damage via different pathomechanisms, notably granulomatous inflammation (eg, nodular dermatitis, osteomyelitis), immune complex deposition (eg, glomerulonephritis), and/or autoantibody production (eg, polymyositis). This is a compensatory but detrimental mechanism generated mainly because of the insufficient killing capacity of macrophages against the parasite in the susceptible dog. Clinical disease is typically exemplified as exfoliative and/or ulcerative dermatitis, with or without nasodigital hyperkeratosis and onychogryphosis, glomerulonephritis, atrophic myositis of masticatory muscles, anterior uveitis, keratoconjunctivitis sicca, epistaxis, and/or polyarthritis, appearing alone or in various combinations. The pathogenesis of these clinical conditions has recently been highlighted, to a greater or lesser extent. The usually subclinical conditions expressed as chronic colitis, chronic hepatitis, vasculitis, myocarditis, osteomyelitis, orchiepididymitis, and meningoencephalomyelitis, though uncommon, are of pathologic importance from a differential point of view. The leading cause of death among canine leishmaniasis patients is chronic proteinuric nephritis that may progress to end-stage kidney disease, nephrotic syndrome, and/or systemic hypertension. However, even the asymptomatic proteinuria, when profuse, may be a serious problem because it predisposes to arterial thromboembolism and eventually contributes to the deterioration of the body condition.

Parasitological diagnosis of canine visceral leishmaniasis: is intact skin a good target?

The objective of this study was to evaluate intact skin of seroreactive dogs as a possible target for the parasitological confirmation of canine visceral leishmaniasis (CVL). For this purpose, 394 dogs identified in serological surveys carried out in the metropolitan region of Belo Horizonte were studied. Blood was collected from all animals for serology and a tissue sample was obtained from two sites for parasitological diagnosis. Skin obtained from the ear and scapular region was simultaneously analyzed in 247 animals and lesion samples and ear skin were analyzed in 147 dogs. Leishmania parasites were isolated from 310 (78.7%) animals, and all isolates were identified as Leishmania chagasi. Simultaneous isolation from two sites was possible in 240 of the 310 animals, including ear and scapular skin in 151/247 (61.1%) and ear skin and skin lesions in 89/147 (60.5%). Ours results suggest that intact skin is one of the main target sites for the parasitological confirmation of CVL in seroreactive dogs.

Cutaneous sterile granulomas/pyogranulomas, leishmaniasis and mycobacterial infections

Cutaneous "sterile" granulomas represent a group of uncommon skin disorders of unknown aetiopathogenesis. Many diseases are included in this group (for example, sterile granuloma/pyogranuloma syndrome and reactive histiocytosis). The definition of sterile is based on the exclusion of other possible aetiological agents (for example, microorganisms or foreign body). Many techniques are used to rule out a microbial aetiology including cytology, histology, immunohistochemistry and culture. However, some organisms are "fastidious" and difficult to culture or to identify with routine methods, and molecular studies are necessary. This is particularly true for mycobacteria (for example, canine leproid granuloma syndrome) and Leishmania. Recently, studies in human and veterinary medicine have proved the presence of microorganisms (mycobacteria and Leishmania) using a polymerase chain reaction technique in specimens previously diagnosed as sterile. Therefore, it is very important, with the development of new technologies, to use a multidisciplinary diagnostic approach to definitively rule out any microorganism before declaring a disease sterile.