Presence of anti-platelet IgM and IgG antibodies in dogs naturally infected by Leishmania infantum

Thirty-three dogs, naturally infected by Leishmania infantum, were enrolled in the study and were classified as oligo-symptomatic (n. 15) and symptomatic or markedly symptomatic (n. 18). A control group was 10 healthy dogs. A haematological profile was obtained and the dogs serum was employed to assess the presence of platelet binding IgM and IgG antibodies (PBIgM, PBIgG) using flow cytometry. FITC labelled goat anti-dog IgM or IgG were used to detect PBIgM and PBIgG. Samples with a mean fluorescence intensity (MFI) that was 100 channels higher on a log scale for more than 30% of the platelets than seen in negative control platelets from a healthy dog were considered positive for the presence of anti-platelet antibodies (PBIg). Twenty-one (63.3%) dogs revealed the presence of PBIg. Six of them were oligo-symptomatic while 15 showed moderate or severe clinical signs of illness. All the dogs with PBIg showed the presence of PBIgM, with nine animals showing both PBIgM and PBIgG. Nine of 18 symptomatic or markedly symptomatic dogs showed thrombocytopenia, while normal platelet counts were observed in all oligo-symptomatic animals. Eight of 9 thrombocytopenic animals showed the presence of PBIgM, while six of them showed PBIgG. One thrombocytopenic dog was negative for PBIg. This study is the first report documenting the presence of PBIg in natural canine leishmaniasis implying a pathogenic association between thrombocytopenia and the presence of antibody against platelet membrane.     

Immune response against Leishmania antigens in dogs naturally and experimentally infected with Leishmania infantum

Cell-mediated and humoral immune response in naturally and experimentally infected dogs was studied using crude and pure antigens. Both types of infections induced severe signs of visceral disease, but the symptoms observed in natural infections were more pronounced than in experimental infections. In addition, asymptomatic infections were not observed in experimentally infected animals. Disease evolution in laboratory infections was rapid and an increase in antibody titer to crude parasite antigen was correlated with the appearance and aggravation of clinical symptoms. Peripheral blood lymphocyte proliferation to crude antigen and pure gp63 was observed early following experimental infection, but was abolished once the infected dogs began to exhibit clinical signs. A similar pattern was observed in naturally infected dogs. Serum from all patent dogs showed high antibody titers to rK39 in enzyme-linked immunosorbent assays (ELISA), and reacted by western blotting with several antigens, 12 to 120 KDa, including gp63 and gp70. In the case of asymptomatic dogs. antibody titers to crude antigen were low and only a few antigens were identified by western blotting. None of the pure proteins examined, gp63, gp70, and rK39 were recognized by western blotting or ELISA. However, asymptomatic dogs exhibited specific lymphocyte proliferation to both crude antigen and the potential vaccine candidate gp63.     

Comparison of monoclonal and polyclonal antibodies for the detection of canine IgG1 and IgG2, and associations with infection outcome in Leishmania infantum naturally infected dogs

In murine models of leishmaniasis, IgG subclass expression is a proxy measure for Th1/Th2 cellular immune response bias. However, in dogs, the reservoir of zoonotic visceral leishmaniasis, no consistent association has been described between IgG subclass ratios and disease resistance. Inconsistent results may reflect lack of specificity of commonly used commercial antibodies. Our aim was to measure IgG1 and IgG2 responses to crude Leishmania antigen using commercial polyclonal antibodies for comparison with a panel of commercially unavailable monoclonal antibodies, in a cohort of 60 naturally infected dogs, and to compare associations between subclass responses and clinical or parasitological outcomes. IgG1 and IgG2, measured by both antibodies, were higher in clinically symptomatic than in asymptomatic dogs (P ≤ 0.03), reflecting general upregulation of IgG in infected dogs. Unlike the murine model, canine IgG2:IgG1 ratios were not predictive of clinical or parasitological outcomes of infection. Associations between subclass levels and positivity by bone marrow culture and PCR were not consistent when measured with different antibodies. Further research is needed to re-evaluate the specificity of commercially available IgG subclass antibodies.     

Histopathological and parasitological study of the gastrointestinal tract of dogs naturally infected with Leishmania infantum

Background

The aim of this study was to provide a systematic pathological and parasitological overview of the gastrointestinal tract (GIT), including the stomach, duodenum, jejunum, ileum, caecum and colon, of dogs naturally infected with Leishmania.

Methods

Twenty mongrel dogs naturally infected with Leishmania (Leishmania) infantum and obtained from the Control Zoonosis Center of the Municipality of Ribeirão das Neves, Belo Horizonte Metropolitan area, Minas Gerais (MG) state, Brazil, were analyzed. The dogs were divided into two groups: Group 1 comprised nine clinically normal dogs and group 2 comprised 11 clinically affected dogs. After necropsy, one sample was collected from each GIT segment, namely the stomach, duodenum, jejunum, ileum, caecum and colon. Furthermore, paraffin-embedded samples were used for histological and parasitological (immunohistochemistry) evaluation and a morphometrical study were carried out to determine the parasite load (immunolabeled amastigote forms of Leishmania). The Friedman and the Mann Whitney tests were used for statistical analysis. The Friedman test was used to analyze each segment of the GIT within each group of dogs and the Mann Whitney test was used to compare the GIT segments between clinically unaffected and affected dogs.

Results

The infected dogs had an increased number of macrophages, plasma cells and lymphocytes, but lesions were generally mild. Parasite distribution in the GIT was evident in all intestinal segments and layers of the intestinal wall (mucosal, muscular and submucosal) irrespective of the clinical status of the dogs. However, the parasite load was statistically higher in the caecum and colon than in other segments of the GIT.

Conclusion

The high parasite burden evident throughout the GIT mucosa with only mild pathological alterations led us to consider whether Leishmania gains an advantage from the intestinal immunoregulatory response (immunological tolerance).     

Cytologic patterns of lymphadenopathy in dogs infected with Leishmania infantum

BACKGROUND: Lymphadenopathy in canine leishmaniosis has been reported as reactive lymphoid hyperplasia or granulomatous (histiocytic) lymphadenitis. However, we are unaware of information on the effect of latent Leishmania infection on lymph node cytology compared with clinically affected dogs. OBJECTIVES: The aim of the present study was to investigate cytologic patterns of lymphadenopathy in dogs with clinical and subclinical forms of leishmaniosis and to correlate cytologic findings with the density of Leishmania amastigotes in fine needle aspiration (FNA) smears. METHODS: FNA cytology of prescapular or popliteal lymph nodes was evaluated on 32 dogs with clinical evidence of leishmaniosis (group A), 24 subclinically infected dogs (group B), and 17 clinically healthy noninfected dogs (group C); groups were based on the results of serologic and PCR tests for Leishmania sp. Differential nucleated cell counts (based on 300 cells) and amastigote density were determined microscopically. Cytologic findings were categorized and compared among groups. RESULTS: Cytologic abnormalities were found in 19 of 32 (59.4%) dogs in group A, 1 of 24 (4.2%) dogs in group B, and 2 of 17 (11.8%) dogs in group C and were significantly more frequent in group A than group B (P <.001) or C (P = .001). In group A, 68.7% of the dogs had lymphoid hyperplasia, 12.5% had lymphoid hyperplasia and histiocytic lymphadenitis, 6.3% had histiocytic lymphadenitis, and 3.1% had lymphoid hyperplasia and neutrophilic lymphadenitis. Lymphoid hyperplasia was also noted in 1 dog in group B, and lymphoid hyperplasia and eosinophilic lymphadenitis were each found in 1 dog in group C. Lymph node smears from 31 (96.9%) dogs in group A and 6 (25%) dogs in group B were positive for Leishmania amastigotes; however, no correlation was found between the density of amastigotes and cytopathologic patterns of lymphadenopathy. CONCLUSION: Abnormal lymph node cytology is much more common in dogs with clinical leishmaniosis than in dogs with subclinical infection, and primarily involves lymphoid hyperplasia. Despite finding no association between the density of amastigotes and type of lymphadenopathy, lymph node cytology still is a valuable diagnostic tool for diagnosing canine leishmaniosis.     

Infection of sandflies by a cat naturally infected with Leishmania infantum

Despite the recent reports of feline leishmaniosis from Southern Europe, cats are still regarded as unusual Leishmania hosts. A cat found chronically infected with Leishmania was submitted to xenodiagnosis. After being sedated, the animal was exposed to the bite of 100 laboratory-reared Phlebotomus perniciosus in a fine net cage for 90 min. Four out of 19 blood-fed sandflies (21%) showed motile promastigotes at the dissection. Parasites cultured from cat's lymph node and an infected fly were identical at PCR-RFLP genotyping and identified as Leishmania infantum MON-1, the main zymodeme responsible for human and canine leishmaniosis in Southern Europe. This is the first evidence of transmissibility of feline parasites to a proven vector, suggesting that cats may represent an additional domestic reservoir for L. infantum.     

Leishmania DNA load and cytokine expression levels in asymptomatic naturally infected dogs

The factors responsible for the clinical progress of visceral leishmaniasis (VL) in dogs have not been yet established. The starting hypothesis was the possibility of associating the changing level of a specific type of cytokines with the evolution of the infection towards infection-manifested disease or resistant behaviour. For this purpose the authors have established a connection between Leishmania load, cytokine mRNA accumulation, and the progression of the disease in naturally infected asymptomatic dogs. We made use of real-time (RT) PCR system to detect the expression of cytokine mRNA levels during all the phases of the infection. In particular, we measured the amount of parasites in samples such as blood, lymph nodes and skin, and the expression levels of IFN-gamma, IL-2, IL-4, IL-10, IL-12 and IL-18 cytokines in the blood. We employed different targeted real-time PCR assay on 40 naturally infected dogs, initially asymptomatic; 20 of these progressed to overt disease, and the 20 remaining dogs remained asymptomatic throughout the period of study (2 years). Two other groups included: 20 naturally infected dogs with clinical signs of VL, and 20 healthy dogs living in a non-endemic area. All these animals were employed as positive and negative controls, respectively. The overall results obtained demonstrate that the simultaneous evaluation of parasites and cytokine levels represents a reliable tool for predicting disease development, and thus for choosing the best treatment for the asymptomatic form of the disease.     

Serological, clinical and histopathological changes in naturally infected dogs with Leishmania infantum in the Khemisset province, Morocco

Canine leishmaniasis (canL) is widespread in the north of Morocco and the Leishmania infantum local strains are highly virulent. An epidemiological survey was carried out in 1993-1995 in the Khemisset province. In this region, the severity of the disease was assessed during regular visits to the identified foci by clinical examination of 323 dogs. Clinical signs were protean and occurred in various combinations. Biopsies were made on available sick dogs; the main histological changes were severe infiltration of the spleen, lymph nodes and bone marrow by mononuclear cells and hyperplasia of macrophage cells with amastigotes in their cytoplasm. The seroprevalence among 323 dog sera tested by ELISA showed a rate of 16.71%. The highest prevalence of the disease was 23.6% in the Sid El Ghandour hamlet. A comparison of the results of this study with those from the year following the first examination on the same site (Sid El Ghandour) of 67 dogs showed that the disease prevalence had not increased significantly (23.6% to 25.33%).     

Antileishmanial antibody profile in dogs naturally infected with Leishmania chagasi

Visceral leishmaniasis (VL) presents vigorous Th2 immune response, which is mainly characterized in human by augmented expression of Il-4, polyclonal B cell activation, intense hypergammaglobulinemia and production of antileishmanial IgE antibodies. However, few aspects of this type of immune response have been demonstrated in studies of canine visceral leishmaniasis (CVL). This work investigated by ELISA and western immunoblotting the production of antileishmanial IgE antibodies (IgE Ab) in symptomatic and asymptomatic dogs naturally infected by Leishmania chagasi, and also compared this IgE immune response with those of IgG, IgG1 and IgG2 antibodies. Three groups of dogs were evaluated: 12 VL dogs with positive Leishmania biopsies (GI), 44 dogs with a positive leishmanial indirect fluorescent antibody test (IFAT), 30 of them presenting clinical signs of VL and 14 asymptomatic (GII) and 21 healthy dogs living in kennels located in leishmaniasis endemic areas (GIII), which were seronegative in the IFAT. Eighteen dogs from an area free of CVL were used as controls (GIV). Antileishmanial IgE antibodies were detected in 4 of 12 VL dogs from group I (33%) and 14 of 30 symptomatic dogs from group II (47%). While all asymptomatic dogs from group II (100%) were seronegative for antileishmanial IgE Ab, 7 of 21 healthy animals from group III (33%) had these immunoglobulins. A strong correlation was verified between antileishmanial IgG and IgG2 antibody titers in all symptomatic dogs, but only 15 of these 42 animals (36%) produced simultaneously IgE, IgG, IgG1 and IgG2 antibodies to Leishmania. IgE antibodies recognized leishmanial antigens of 12, 36, 61, 81 and 118 KDD, while a more complex pattern of immunoblotting was verified mainly for IgG and IgG2 antibodies from symptomatic animals. IgG1 and IgG2 antibodies shared the recognition of L. chagasi polypeptides of 118, 81, 61, 36, 18, 14 and 12 KDD, being more intense the immune reactions between IgG1 Ab and the leishmanial polypeptides of 61 and 36 KDD, and also between IgG2 antibodies and the antigens of 26, 21, 18, 14 and 12 KDD. Our results suggest that the polyclonal production of antileishmanial antibodies that includes IgE Ab could characterize a Th2 immune response in CVL and can help the laboratory diagnosis of this disease.     

Neurological manifestations in dogs naturally infected by Leishmania infantum: descriptions of 10 cases and a review of the literature

In order to evaluate possible nervous system involvement in canine leishmaniasis, retrospective evaluation of all medical records of leishmaniotic dogs exhibiting neurological signs referred to our hospital over a 5‐year period was performed. The records of 10 dogs were reviewed. Depending on the neuroanatomical localisation, the dogs underwent advanced diagnostic imaging, cerebrospinal fluid analysis, electrodiagnostic testing and histopathologic evaluations. The final neurological diagnosis was: meningoencephalitis (n=2), brain haemorrhagic stroke (n=1), haemorrhagic choroiditis (n=1), meningomyelitis (n=2), ischaemic myelopathy (n=1), polymyositis (n=2) and peripheral neuropathy (n=1). This study confirms that both central and peripheral nervous systems can be affected by leishmaniasis and provides an overview on the possible etiopathogenetic mechanisms. In addition, clinical and diagnostic findings, therapy and follow‐up of affected dogs are described.     

Longitudinal analysis of cytokine gene expression and parasite load in PBMC in Leishmania infantum experimentally infected dogs

Canine visceral leishmaniasis (CVL) is caused by Leishmania infantum, an intracellular protozoan parasite that causes a severe infectious disease. To evaluate the gene expression profile associated to CVL in vivo, we have measured monthly by real-time PCR over one year the IL-4, IL-10, IL-12, IL-13, IFN-gamma, TGF-beta and TNF-alpha mRNA levels in peripheral blood mononuclear cells in 6 experimentally infected dogs that exhibited different progressions of the illness. While in two dogs no parasite, or a very low number of parasites, was detected and the two dogs did not show any clinico-pathological abnormalities at the end of the study (L dogs), for the remaining dogs high parasite loads were detected and they developed clinical leishmaniasis (H dogs). The L dogs have null expression of both IL-4 and IL-13 for the first 4 months after the infection, whereas an early IL-4 and IL-13 expression occurs in this period of infection in most of the dogs that developed clinical leishmaniasis (H dogs). Furthermore, a higher IFN-gamma expression was associated with the increase of parasite load and clinical status in these dogs. Moreover, the high variability of expression at the pre-infection stage causes us to reject the possibility that the basal levels of these cytokines indicate the prognosis of the subsequent response against infection.     

Platelet aggregation and haemostatic response in dogs naturally co-infected by Leishmania infantum and Ehrlichia canis

Haemostatic alterations in dogs naturally infected by ehrlichiosis and/or leishmaniasis were studied. Platelet count, ADP and collagen-induced platelet aggregation, prothrombin time, activated partial thromboplastin time (APTT) and plasma fibrinogen concentration were measured. An evident reduction of platelet aggregation response was shown for Leishmania-Ehrlichia co-infected dogs where platelet aggregation was lower in comparison with control and leishmaniotic dogs (ADP and collagen, P < or = 0.01) and ehrlichiotic dogs (ADP 10 and 7.5 microm, P < or = 0.05). Moreover, a significant increase in APTT as well as a reduction of the albumin/globulin rate (A/G) for leishmaniotic and co-infected dogs versus control and ehrlichiotic dogs was detected. The hypothesis of a synergism between leishmaniosis and ehrlichiosis in altering platelet function by different pathways is discussed.     

Serological and parasitological follow-up in dogs experimentally infected with Leishmania infantum and treated with meglumine antimoniate.

Six healthy beagle dogs were infected with Leishmania infantum (MCAN/ES/92/BCN-83/MON-1) by intravenous inoculation of 5 x 10(7) promastigotes and two others were used as controls. When animals showed clinical signs of disease at 29, 37, 41 and 45 weeks post-infection (p.i.), they were treated with meglumine antimoniate (20.4 mg Sb/kg/12 h) subcutaneously for two periods of 10 days each. Sera were tested periodically for Leishmania antibodies by Dot-ELISA, ELISA and Western blot (WB). Aspirates of popliteal lymph node (PLN), peripheral blood sample (PB) and healthy skin were cultured in NNN and Schneider's medium. PLNs were positive between 8 and 20 weeks p.i. and in one animal PB was positive 6 weeks p.i. Samples of healthy skin, obtained before treatment, were also positive. Dot-ELISA and ELISA detected specific antibodies at an early stage between 4 and 12 weeks p.i and surpassed the cut-off between 16-24 weeks p.i., while the WB was positive between 10-19 weeks p.i. The pattern of bands revealed during the first stages of infection was variable and only in two cases did the positivity start with bands of low molecular weight (12-14 kD); the number of bands increased until 15-24 weeks p.i., after which sera revealed a complete pattern of bands, from 12 to 85 kD, in the antigen of Leishmania. After treatment the clinical improvement of the animals was accompanied by a decrease in antibody titers (Dot-ELISA and ELISA) although the parasites remained in the PLN. This was reflected in the WB by a decrease in the intensity of bands, especially those in the region of 12-30 kD. A new increase in the antibody levels between 3 and 5 months after terminating the therapy was detected in the WB by a restoration of the initial complete pattern of bands.     

Changes in the plasma concentrations of lipids and lipoprotein fractions in dogs infected with Leishmania infantum.

A study was made of serum concentrations of cholesterol, phospholipids, triglycerides, cholesterol bound to high-density lipoproteins (HDL), HDL1-cholesterol, HDL2-cholesterol and cholesterol bound to low-density lipoproteins (LDL) in 16 dogs naturally infected with Leishmania infantum (ZMON-1) taken from an endemic focus. Results were compared with those of a control group of ten healthy dogs. Statistically significant increases in cholesterol, triglyceride and LDL-cholesterol levels were observed. There was, however, a statistically significant decrease in HDL-cholesterol level, mainly at the expense of the HDL2-cholesterol subfraction. Cholesterol transport is therefore shown to undergo changes which may be attributed to the consumptive evolution of the disease, immunocomplex deposits in cells, hepatic disorders and interactions between the parasite and the normal cholesterol metabolism of the host.