Detailed analysis of an experimental challenge model for Leishmania infantum (JPC strain) in dogs

Antileishmanial efficacy and tolerability of combined treatment with non-ionic surfactant vesicle formulations of sodium stibogluconate and paromomycin in dogs

Infection with Leishmania infantum causes the disease visceral leishmaniasis (VL), which is a serious clinical and veterinary problem. The drugs used to treat canine leishmaniasis (CanL) do not cause complete parasite clearance; they can be toxic, and emerging drug resistance in parasite populations limits their clinical utility. Therefore, in this study we have evaluated the toxicity and efficacy of joint treatment with a 1:1 mixture of sodium stibogluconate-NIV (SSG-NIV, 10 mg Sb^v/day) and paromomycin-NIV (PMM-NIV, 10 mg PMM/kg/day), given intravenously daily for seven days from day 270 post-infection, to nine-month-old female beagle dogs (n = 6) experimentally infected with Leishmania infantum. Treatment significantly improved the clinical symptoms of VL infection in all the treated dogs, reduced parasite burdens in lymph nodes and bone marrow, and all symptomatic treated dogs, were asymptomatic at 90 days post-treatment. Treatment was associated with a progressive and significant decrease in specific IgG anti-Leishmania antibodies using parasite soluble antigen (p < 0.01) or rK39 (p < 0.01) as the target antigen. In addition, all dogs were classified as parasite negative based on Leishmania nested PCR and quantitative real time PCR tests and as well as an inability to culture of promastigote parasites from lymph nodes and bone marrow tissue samples taken at day 90 post-treatment. However, treatment did not cure the dogs as parasites were detected at 10 months post-treatment, indicating that a different dosing regimen is required to cause long term cure or prevent relapse.

Early antibody response and clinical outcome in experimental canine leishmaniasis

Infected dogs are the main reservoir of zoonotic visceral leishmaniasis, a widespread parasitic disease caused by Leishmania infantum. Therefore, the control of canine infections is required to reduce the incidence of human cases. Disease outcome in dogs depends on the fine balance between parasite virulence and efficacy of the immune system. Thus, knowledge of early response could yield relevant information for diagnosis and follow-up. In our study, 20 Beagle dogs were intravenously infected with 10⁸ amastigotes of a fresh isolate of L. infantum and monitored along 16 weeks post inoculation. Specific antibody response and clinical evolution of infected animals were highly variable. Immunofluorescence antibody test (IFAT) and enzyme linked immunosorbent assay (ELISA) were useful to assess infection status, although only ELISA with promastigote-coated plates and, particularly, western blotting (WB) allowed an early diagnosis. Prominent antigens were identified by mass peptide fingerprinting. Chaperonin HSP60, 32 and 30 KDa antigens were recognized by all dogs on week 10 post infection. This suggests that these antigens may be valuable for early diagnosis. Advanced infection showed, in addition, reactivity to HSP83 and HSP70. Disease outcome did not show a clear relationship with ELISA or IFAT titers. Correlation between the clinical status and the combined reactivity to some antigens sustains their use for diagnosis and follow-up.

Immunohistochemical study of renal fibropoiesis associated with dogs naturally and experimentally infected with two different strains of Leishmania (L.) infantum

The objectives of this work were to study some pathological aspects of kidneys obtained from dogs naturally infected with Leishmania infantum and from dogs experimentally infected with two different strains of L infantum with special emphasis on fibrotic process. Seventy eight specimens of paraffin-embedded kidney fragments were collected as follows: (a) CNI group composed by 62 kidney samples of adult mongrel dogs, naturally infected with L infantum; (b) BH401 group composed by five kidney samples of adult Beagles experimentally infected with L infantum strain MCAN BR/2002/BH401; (c) BH400 group composed by eleven kidney samples of adult Beagles experimentally infected with L infantum strain MCAN/BR/2000/BH400, at the same dose and same route of the previous group, denominated group BH400; Control group (CC) composed by four kidney samples of adult Beagles. All animals revealed glomerular and interstitial fibropoiesis associated with different types of glomerulonephritis and chronic interstitial nephritis. Fibrosis was markedly more intense in the BH401 group, followed by animals in the CNI group. Markers for myofibroblasts (mesenchymal markers) such as alpha-actin (α-SMA), vimentin and the cytokine transforming growth factor beta (TGF-β) were done by immunohistochemistry. BH401 group showed higher expression of all these markers than others. Intracellular amastigotes forms of Leishmania was mainly found in BH401. These results could be indicating that the MCAN/BR/2002/BH401 strain is a good choice for the study of renal LVC experimental model.

Inconsistent MHC class II association in Beagles experimentally infected with Leishmania infantum

The clinical outcome of Leishmania infantum infection in dogs varies from subclinical infection to severe disease. Researchers attribute this variability in clinical manifestations to the ability of the immune response to limit pathogen multiplication and dissemination, which is, in part, likely determined by the immune response genes. The aim of this study was to test the hypothesis that MHC class II genes are associated with disease outcome of experimental L. infantum infection in Beagles. Dog leukocyte antigen (DLA) class II haplotypes were characterised by sequence-based typing of Beagle dogs experimentally infected with L. infantum during vaccine challenge studies. Variability of response to infection was determined by clinical score, serology and quantification of L. infantum DNA in the bone marrow over the study period. Dogs showed limited DLA diversity and the DLA profiles of dogs recruited for the different vaccine challenge studies differed. There were variable responses to infection, despite the apparent restriction in genetic diversity. One haplotype DLA-DRB1*001:02-DQA1*001:01-DQB1*002:01 was associated with increased anti-Leishmania antibodies in one infection model, but no DLA associations were found in other groups or with parasite load or clinical score. Examination of this particular DLA haplotype in a larger number of dogs is required to confirm whether an association exists with the immune or clinical responses to L. infantum infection.

Resequencing of the Leishmania infantum (strain JPCM5) genome and de novo assembly into 36 contigs

Leishmania parasites are the causative of leishmaniasis, a group of potentially fatal human diseases. Control strategies for leishmaniasis can be enhanced by genome based investigations. The publication in 2005 of the Leishmania major genome sequence, and two years later the genomes for the species Leishmania braziliensis and Leishmania infantum were major milestones. Since then, the L. infantum genome, although highly fragmented and incomplete, has been used widely as the reference genome to address whole transcriptomics and proteomics studies. Here, we report the sequencing of the L. infantum genome by two NGS methodologies and, as a result, the complete genome assembly on 36 contigs (chromosomes). Regarding the present L. infantum genome-draft, 495 new genes have been annotated, a hundred have been corrected and 75 previous annotated genes have been discontinued. These changes are not only the result of an increase in the genome size, but a significant contribution derives from the existence of a large number of incorrectly assembled regions in current chromosomal scaffolds. Furthermore, an improved assembly of tandemly repeated genes has been obtained. All these analyses support that the de novo assembled L. infantum genome represents a robust assembly and should replace the currently available in the databases.

Canine visceral leishmaniasis follow-up: a new anti-IgG serological test more sensitive than ITS-1 conventional PCR

Visceral leishmaniasis (VL) is a neglected tropical disease with dogs serving as reservoirs for one of its etiological agents, Leishmania infantum. In Brazil, VL control involves culling of seropositive dogs, among other actions. However, the most employed serological tests lack accuracy, and are not able to detect canine visceral leishmaniasis (CVL) during the early stages of infection. Early detection of CVL is highly desirable in order to shorten the contact time between the infected reservoirs and the vectors. In this study, we investigated the ability of two multiepitope proteins, PQ10 and PQ20, to detect CVL at earlier stages than currently employed methods, including ITS-1 conventional PCR. Using serum samples from naturally infected dogs, we observed that ELISA-PQ10 and ELISA-PQ20 were able to detect Leishmania infection at earlier time points as compared with kDNA PCR-RFLP in anti-IgG and anti-IgM assays. Using sera from experimentally infected dogs, we monitored seroconversion using multiepitope proteins, ELISA-crude antigen, as well as ITS-1 conventional and real-time PCR. While seroconversion was detected by ELISA-crude antigen in 16.6% of the dogs, multiepitope proteins were able to detect seroconversion in more than 80% of them. Moreover, the ability of ELISA-PQ10 and ELISA-PQ20 to detect Leishmania infection at earlier time points as compared with conventional PCR was also confirmed in experimental infection dogs' sera. Immunofluorescence to Babesia canis and Ehrlichia canis did not show cross-reactions with ELISA-PQ10/PQ20 positive samples. Results of real-time PCR and ELISA with multiepitope proteins were very similar, with concordances between 80 and 100%. Furthermore, our findings indicated that PQ10 and PQ20 immunoassays can be related to parasite load. ELISA-PQ10 and ELISA-PQ20 are more sensitive diagnostic tools for early CVL detection as compared with other methods They could potentially be used in screening tests due to easy execution and low costs facilities.

Treatment of canine leishmaniasis with marbofloxacin in dogs with renal disease

Treatment of canine leishmaniasis (CanL) represents a challenge. Due to the high prevalence of renal disease associated to CanL, it is important to find an effective drug that does not damage the kidneys. Marbofloxacin has been shown to be effective and well tolerated in non-azotemic dogs with leishmaniasis. To evaluate the safety and efficacy of marbofloxacin in dogs with leishmaniasis and decreased renal function, 28 dogs suffering from leishmaniasis and chronic kidney disease (CKD) were treated with oral marbofloxacin at 2 mg/Kg/day for 28 days. During treatment dogs were assessed by performing weekly physical exams, measuring blood pressure and evaluating blood and urine parameters. Lymph node aspirations were also obtained at days 0 and 28. The global clinical score decreased significantly, from 6.2±3.4 to 4.7±3.1 (p = 0.0001), after treatment. Marbofloxacin also decreased parasitic load in 72% of the dogs. No significant differences in plasma creatinine, urine specific gravity, urinary concentrations of cystatin C, ferritin and urinary protein loss were detected during treatment. A transient but significant decrease in blood pressure was detected up to day 14 (from 180.1±36.6 to 166.0±32.7 mmHg; p = 0.016). Moreover, dogs showed a significant increase in plasma albumin concentration (from 15.0±5.2 to 16.6±3.9 g/L; p = 0.014) and a significant decrease in globulin concentration (from 59.0±18.1 to 54.1±18.0 g/L; p = 0.005). The results demonstrate that, in addition to being effective for treatment of CanL, marbofloxacin is a very safe drug in dogs with CKD and leishmaniasis.

Immunogenicity in dogs and protection against visceral leishmaniasis induced by a 14kDa Leishmania infantum recombinant polypeptide

In areas were human visceral leishmaniasis (VL) is endemic, the domestic dog is the main parasite reservoir in the infectious cycle of Leishmania infantum. Development of prophylactic strategies to lower the parasite burden in dogs would reduce sand fly transmission thus lowering the incidence of zoonotic VL. Here we demonstrate that vaccination of dogs with a recombinant 14kDa polypeptide of L. infantum nuclear transport factor 2 (Li-ntf2) mixed with adjuvant BpMPLA-SE resulted in the production of specific anti-Li-ntf2 IgG antibodies as well as IFN-γ release by the animals' peripheral blood mononuclear cells stimulated with the antigen. In addition, immunization with this single and small 14kDa poplypeptide resulted in protracted progression of the infection of the animals after challenging with a high dose of virulent L. infantum. Five months after challenge the parasite load was lower in the bone marrow of immunized dogs compared to non-immunized animals. The antibody response to K39, a marker of active VL, at ten months after challenge was strong and significantly higher in the control dogs than in vaccinated animals. At the study termination vaccinated animals showed significantly more liver granulomas and lymphoid hyperplasia than non-vaccinated animals, which are both histological markers of resistance to infection. Together, these results indicate that the 14kDa polypeptide is an attractive protective molecule that can be easily incorporated in a leishmanial polyprotein vaccine candidate to augment/complement the overall protective efficacy of the final product.

Efficacy of Recombinant Canine Distemper Virus Expressing Leishmania Antigen against Leishmania Challenge in Dogs

Canine distemper virus (CDV) vaccination confers long-term protection against CDV reinfection. To investigate the utility of CDV as a polyvalent vaccine vector for Leishmania, we generated recombinant CDVs, based on an avirulent Yanaka strain, that expressed Leishmania antigens: LACK, TSA, or LmSTI1 (rCDV-LACK, rCDV-TSA, and rCDV-LmSTI1, respectively). Dogs immunized with rCDV-LACK were protected against challenge with lethal doses of virulent CDV, in the same way as the parental Yanaka strain. To evaluate the protective effects of the recombinant CDVs against cutaneous leishmaniasis in dogs, dogs were immunized with one recombinant CDV or a cocktail of three recombinant CDVs, before intradermal challenge (in the ears) with infective-stage promastigotes of Leishmania major. Unvaccinated dogs showed increased nodules with ulcer formation after 3 weeks, whereas dogs immunized with rCDV-LACK showed markedly smaller nodules without ulceration. Although the rCDV-TSA- and rCDV-LmSTI1-immunized dogs showed little protection against L. major, the cocktail of three recombinant CDVs more effectively suppressed the progression of nodule formation than immunization with rCDV-LACK alone. These results indicate that recombinant CDV is suitable for use as a polyvalent live attenuated vaccine for protection against both CDV and L. major infections in dogs.

Long-term follow-up of dogs with leishmaniosis treated with meglumine antimoniate plus allopurinol versus miltefosine plus allopurinol

BACKGROUND

Visceral leishmaniosis is a potentially life-threatening illness caused by a protozoan parasite of the genus Leishmania. It is found mainly in areas where both the parasite and its vector are endemic and is one of the most challenging infectious diseases in the world to control. HIV infected patients are vulnerable to Leishmania infections, and the main reservoir hosts of Leishmania infantum parasites are domestic dogs. Here, we evaluated the long-term efficacy of treatment with meglumine antimoniate plus allopurinol (G1) compared to miltefosine plus allopurinol (G2) in dogs naturally infected L. infantum.

METHODS

Eighteen dogs with leishmaniosis were divided into the following two groups: G1 (n = 9) was treated subcutaneously with meglumine antimoniate (100 mg/kg/day/30 days) plus allopurinol (10 mg/kg/per day/30 days), while G2 (n = 9) was treated orally with miltefosine (2 mg/Kg/day/30 days) plus allopurinol (10 mg/kg/day/30 days). Thereafter, the same dose of allopurinol was administered to both groups for 6 years. Leishmania DNA in lymph node aspirates from the G1 and G2 dogs was quantified by real-time quantitative PCR at baseline and every 3 months for 24 months, and then at 28, 36, 48, 60 and 72 months. At each assessment, the dogs were examined for signs of disease, and their clinical scores were recorded.

RESULTS

Both combination therapies produced significant clinical improvements in the dogs, with a significant reduction in the parasitic load in the lymph nodes of the dogs from both groups after 3 months of treatment. Clinical relapses were observed in four dogs from G2 (miltefosine/allopurinol), and just one dog from G1 (meglumine antimoniate/allopurinol). All dogs that relapsed had increased clinical scores, and increased anti-Leishmania antibody titers and parasitic loads in their lymph nodes.

CONCLUSIONS

Long-term, the clinical and laboratory findings of the G1 dogs were more stable than those of the G2 dogs, thus indicating that meglumine antimoniate had better clinical efficacy than miltefosine. The results suggest that treatment with allopurinol as a maintenance therapy is crucial for stabilizing the care of canine leishmaniosis.

A canine model of experimental infection with Leishmania (L.) mexicana

BACKGROUND

Cutaneous leishmaniasis is a tropical disease affecting over one million patients annually and Leishmania (L.) mexicana is one of the major etiological agents in the Americas. Here we established the first experimental infection of L. (L.) mexicana in canids.

METHODS

Beagle dogs were infected intradermally with culture-derived L. (L.) mexicana. We followed skin ulcer development, histopathological signs, parasite burden and the immune status of the infected dogs.

RESULTS

All infected dogs developed uniform oval-craterform ulcers similar to those observed in humans, associated with mixed T helper 1/T helper 2 immune responses. Parasites were detected in the healed lesions 15 weeks post-infection. Higher anti-Leishmania IgG levels correlated with larger lesions and high IgG1/IgG2 ratio was associated with some level of splenomegaly.

CONCLUSIONS

The canine model described in this work will be of use for further understanding of L. (L.) mexicana immunopathogenensis, and for drug and vaccine development.

The protective immune response produced in dogs after primary vaccination with the LiESP/QA-21 vaccine (CaniLeish®) remains effective against an experimental challenge one year later

Control of canine leishmaniasis is an important objective for the benefit of dogs living in or visiting endemic areas and for public health because of the zoonotic nature of this disease. Resistance or susceptibility to developing canine leishmaniasis after exposure to Leishmania infantum is primarily determined by the ability of the immune system to develop an appropriate Th1-dominated specific response to the parasite. For this reason there is a need for effective canine vaccines that can decrease the number of dogs developing progressive infections. In this study, we followed the impact of the LiESP/QA-21 canine vaccine (composed of excreted-secreted proteins of L. infantum and the QA-21 saponin adjuvant), recently launched commercially in Europe, on selected humoral and cellular immune parameters following an infectious intravenous challenge with L. infantum promastigotes administered one year after the primary vaccine course. We also followed parasitological parameters to determine the parasitological status of the challenged dogs. In contrast to controls, vaccinated dogs retained significantly stronger cell-mediated immune responses against the parasite despite a virulent challenge and had significantly lower mean parasite burdens at the end of the study, associated with a lower probability of developing active infections. These results confirm that the immune responses generated by vaccination with LiESP/QA-21 are still effective against an intravenous challenge one year after the primary vaccine course.

LBSapSal-vaccinated dogs exhibit increased circulating T-lymphocyte subsets (CD4⁺ and CD8⁺) as well as a reduction of parasitism after challenge with Leishmania infantum plus salivary gland of Lutzomyia longipalpis

BACKGROUND

The development of a protective vaccine against canine visceral leishmaniasis (CVL) is an alternative approach for interrupting the domestic cycle of Leishmania infantum. Given the importance of sand fly salivary proteins as potent immunogens obligatorily co-deposited during transmission of Leishmania parasites, their inclusion in an anti-Leishmania vaccine has been investigated in the last few decades. In this context, we previously immunized dogs with a vaccine composed of L. braziliensis antigens plus saponin as the adjuvant and sand fly salivary gland extract (LBSapSal vaccine). This vaccine elicited an increase in both anti-saliva and anti-Leishmania IgG isotypes, higher counts of specific circulating CD8⁺ T cells, and high NO production.

METHODS

We investigated the immunogenicity and protective effect of LBSapSal vaccination after intradermal challenge with 1 × 10⁷ late-log-phase L. infantum promastigotes in the presence of sand fly saliva of Lutzomyia longipalpis. The dogs were followed for up to 885 days after challenge.

RESULTS

The LBSapSal vaccine presents extensive antigenic diversity with persistent humoral and cellular immune responses, indicating resistance against CVL is triggered by high levels of total IgG and its subtypes (IgG1 and IgG2); expansion of circulating CD5⁺, CD4⁺, and CD8⁺ T lymphocytes and is Leishmania-specific; and reduction of splenic parasite load.

CONCLUSIONS

These results encourage further study of vaccine strategies addressing Leishmania antigens in combination with proteins present in the saliva of the vector.

Leishmania amastigotes in the central nervous system of a naturally infected dog

A 4-year-old male Labrador Retriever dog was presented with a 10-day history of tetraplegia, depression, and absent postural reflexes. The cerebrospinal fluid was positive for Leishmania spp. DNA. At necropsy, a 2-cm long mass was observed adhered to C7 and C8 left spinal nerves. Microscopically, nerve fiber destruction together with mixed inflammatory infiltration was observed in the spinal nerves. Cervical spinal cord sections showed multifocal, diffuse granulomatous inflammation in the white matter. In the brain, perivascular infiltrates were observed in some areas together with subtle pallor of the parenchyma. Immunohistochemistry for Leishmania infantum confirmed the presence of amastigotes in the spinal nerves, spinal cord, brain parenchyma, and choroid plexuses. The current study describes the presence of Leishmania amastigotes in nervous tissue inciting radiculoneuritis, myelitis, and mild meningoencephalitis, suggesting a likely route by which L. infantum amastigotes reach and affect the central nervous system parenchyma.

One-year clinical and parasitological follow-up of dogs treated with marbofloxacin for canine leishmaniosis

The purpose of this international, multicentric, and non-comparative field trial was to obtain complementary data on long-term clinical and parasitological follow-up of dogs treated with marbofloxacin for canine leishmaniosis (CanL). Seventy-four dogs with clinical signs of CanL and without severe renal failure were recruited in France, Spain and Italy, and 61 of them were part of the analysis. Each dog was treated with palatable tablets of marbofloxacin at 2 mg/kg once a day for 28 days. A clinical and parasitological follow-up was performed regularly up to 12 months. Efficacy was demonstrated in 42 dogs (68.9%), within 51 days (mean value), 10 of them (23.8%) being clinically cured after 3 months. A decrease of 61% in the sum of clinical scores was observed after 3 months. Haemato-biochemical parameters improved in general, supporting the observed clinical efficacy. Relapse was observed in 20/38 dogs (52.6%) approximately 5.5 months after treatment completion. The blood parasite load generally developed in conformity with the clinical outcome, even if exceptions were not rare. Lymph nodes remained positive by culture or PCR for a long time, even in dogs for which a good clinical response was observed. Despite the incomplete parasite clearance, as is also the case with other anti-leishmanial drugs, these results nevertheless confirm the relevance of marbofloxacin as a CanL treatment.

Experimental canine leishmaniasis: clinical, parasitological and serological follow-up

Canine leishmaniasis (CanL) caused by Leishmania infantum is transmitted by the bite of phlebotomine sand flies and affects millions of dogs in Europe, Asia, North Africa and South America. Canis familiaris is the major host for these parasites, and the main reservoir for human visceral infection. The development of effective molecules for therapy and immunoprophylaxis, would be an important tool in the control of this zoonosis. The aim of this study was to characterize an experimental CanL model in order to determine the best challenge model and which parameters are the most reliable to evaluate the efficacy of new drugs or vaccine candidates against L. infantum infection. The intravenous challenge with purified amastigotes used in this study allowed the development of infection in all animals inoculated (as confirmed by the detection of parasite in the different tissues and organs collected 6 months after inoculation). Molecular and serologic techniques were efficient methods for the follow-up. Lymph node and bone marrow aspirates were suitable clinical samples to detect the presence of Leishmania parasites. Despite ELISA was highly sensitive in detecting specific anti-Leishmania antibodies the use of two tests can improve the sensitivity and specificity of serological diagnosis.

Molecular diagnosis of canine visceral leishmaniasis: identification of Leishmania species by PCR-RFLP and quantification of parasite DNA by real-time PCR

The efficacies of polymerase chain reaction (PCR) procedures for the diagnosis of canine visceral leishmaniasis (CVL), and of PCR-restriction fragment length polymorphism (RFLP) analysis for the identification of Leishmania species, have been assessed. Quantitative real-time PCR employing a SYBR Green dye-based system was standardised for the quantification of Leishmania kDNA minicircles. Skin, peripheral blood and bone marrow samples collected from 217 dogs, asymptomatic or symptomatic for CVL, were analysed. The PCR method, which was based on the amplification of a 120 bp kDNA fragment conserved across Leishmania species, was able to detect the presence in clinical samples of protozoan parasite DNA in amounts as low as 0.1 fg. Bone marrow and skin samples proved to be more suitable than peripheral blood for the detection of Leishmania by PCR and presented positive indices of 84.9% and 80.2%, respectively. PCR-RFLP analysis indicated that 192 of the PCR-positive dogs were infected with Leishmania infantum chagasi, whilst L. braziliensis was identified in two other animals. Quantitative PCR revealed that bone marrow samples from dogs presenting positive conventional tests contained a higher number of copies of Leishmania kDNA than peripheral blood, although no significant differences were detected between symptomatic and asymptomatic dogs in terms of parasite load. This study demonstrates that PCR can be used for the detection of Leishmania in clinical samples derived from naturally infected dogs, and that PCR-RFLP represents a rapid and sensitive tool for the identification of Leishmania species. Additionally, qPCR is effective in quantifying Leishmania DNA load in clinical samples.

Vaccination of dogs with six different candidate leishmaniasis vaccines composed of a chimerical recombinant protein containing ribosomal and histone protein epitopes in combination with different adjuvants

Chimerical protein "Q", composed of antigenic ribosomal and histone sequences, in combination with live BCG is a promising canine leishmaniasis vaccine candidate; one of the few vaccine candidates that have been tested successfully in dogs. Unfortunately, live BCG is not an appropriate adjuvant for commercial application due to safety problems in dogs. In order to find a safe adjuvant with similar efficacy to live BCG, muramyl dipeptide, aluminium hydroxide, Matrix C and killed Propionibacterium acnes in combination with either E. coli- or baculovirus-produced recombinant JPCM5_Q protein were tested. Groups of five or seven dogs were vaccinated with six different adjuvant-antigen combinations and challenged with a high dose intravenous injection of Leishmania infantum JPC strain promastigotes. All candidate vaccines proved to be safe, and both humoral and cellular responses to the recombinant proteins were detected at the end of the prime-boost vaccination scheme. However, clinical and parasitological data obtained during the 10 month follow-up period indicated that protection was not induced by either of the six candidate vaccines. Although no direct evidence was obtained, our data suggest that live BCG may have a significant protective effect against challenge with L. infantum in dogs.

The effect of phospholipase A2 from Crotalus durissus collilineatus on Leishmania (Leishmania) amazonensis infection

In this study, the effect of phospholipase A2 (PLA2) derived from Crotalus durissus collilineatus was evaluated in vitro and in vivo on experimental cutaneous leishmaniasis. The promastigote and amastigote forms treated with PLA2 presented increased growth rate. In vivo studies showed that PLA2-treated Leishmania (Leishmania) amazonensis promastigotes increased the size of lesions in BALB/c mice, and histopathological analysis showed numerous necrotic regions presenting a higher density of polymorphonuclear, mononuclear, and amastigote cells. Additionally, infected macrophages treated with PLA2 were able to generate prostaglandin E2 (PGE2). Cytokine quantification showed that the supernatant from infected macrophages presented moderate and high amounts of IL-2 and IL-10, respectively. However, in PLA2-treated infected macrophages, suppression of IL-2 levels occurred, but not of IL-10 levels. Observation also revealed that both the supernatant and lysate of L. (L.) amazonensis promastigotes exhibited PLA2 activity, which, in the presence of dexamethasone, showed no reduction in their activities; while glucocorticoid maintained the ability of promastigote forms to infect macrophages, which presented values similar to controls. In conclusion, the results indicate that PLA2 may be a progression factor for cutaneous leishmaniasis, since the PLA2 effect suppressed IL-2 levels and generated PGE2, an inflammatory lipid mediator.

Vaccination with plasmid DNA encoding KMPII, TRYP, LACK and GP63 does not protect dogs against Leishmania infantum experimental challenge

Vaccination of dogs, the domestic reservoir of Leishmania infantum, is the best method for controlling zoonotic visceral leishmaniasis. This strategy would reduce the incidence of disease in both the canine and, indirectly, the human population. Different vaccination approaches have been investigated against canine leishmaniasis (CaL) but to date there is only one licensed vaccine against this disease in dogs, in Brazil. DNA immunization is a promising method for inducing both humoral and cellular immune responses against this parasitic disease. Here, we report the results of a multiantigenic plasmid DNA vaccine encoding KMPII, TRYP, LACK and GP63 L. infantum antigens against experimentally induced CaL. Twelve dogs were randomly assigned to two groups receiving, at a 15 days interval, either four doses of plasmid DNA or similar injections of PBS. After vaccination, dogs were intravenously challenged with 5 x 10(7) promastigotes of L. infantum. The vaccine showed to be safe and well-tolerated. Neither cellular immune response nor antibodies directed against whole Leishmania antigen were detected after immunization in vaccinated dogs, although anti-LACK-specific antibodies were sporadically detected in two vaccinated dogs before challenge, thus suggesting that antigens were indeed expressed. A delay in the development of detectable specific immune response and parasite multiplication in vaccinated dogs was observed after challenge. Nevertheless, the multiantigenic Leishmania DNA vaccine was unable to induce protection against parasite dissemination or disease. This study emphasizes the need to strengthen DNA vaccines in order to obtain effective immune responses in models other than the murine.

The effects of prednisone on haemostasis in leishmaniotic dogs treated with meglumine antimoniate and allopurinol

Thirty dogs naturally infected with Leishmania infantum were studied in order to determine the effects of treatment on haemostatic function. The animals were divided randomly into two treatment groups: Group 1 received meglumine antimoniate and allopurinol; Group 2 dogs were given the same treatment plus prednisone. Ten healthy animals were used as untreated controls. Clinical examination and determination of platelet aggregation, coagulation factors and biochemical parameters were undertaken before treatment and after 15, 30 and 60 days. A significant improvement in platelet aggregation was detected after 60 days in Group 1, but only after 15 days in Group 2. In both treated groups, platelet aggregation was lower than in the control group at the end of the study. The results suggest that prednisone may be a useful tool in the treatment of haemostatic disorders during canine leishmaniosis. The potential benefits and risks due to the use of corticosteroids in the treatment of leishmaniosis are discussed.

Immunization with H1, HASPB1 and MML Leishmania proteins in a vaccine trial against experimental canine leishmaniasis

The protective capabilities of three Leishmania recombinant proteins – histone 1 (H1) and hydrophilic acylated surface protein B1 (HASPB1) immunized singly, or together as a protein cocktail vaccine with Montanide™, and the polyprotein MML immunized with MPL^®-SE adjuvant – were assessed in beagle dogs. Clinical examination of the dogs was carried out periodically under blinded conditions and the condition of the dogs defined as asymptomatic or symptomatic. At the end of the trial, we were able to confirm that following infection with L. infantum promastigotes, five out of eight dogs immunized with H1 Montanide™, and four out of eight dogs immunized with either the combination of HASPB1 with Montanide™ or the combination of H1 + HASPB1 with Montanide™, remained free of clinical signs, compared with two out of seven dogs immunized with the polyprotein MML and adjuvant MPL^®-SE, and two out of eight dogs in the control group. The results demonstrate that HASPB1 and H1 antigens in combination with Montanide™ were able to induce partial protection against canine leishmaniasis, even under extreme experimental challenge conditions.

A long term experimental study of canine visceral leishmaniasis

Previous studies on Leishmania infantum and the canine immune response are derived mainly from short-term studies. To date, there have been no longitudinal studies that perform a serial analysis of the intensity of infection in conjunction with immunological parameters and clinical signs in Leishmania-infected dogs. For this purpose, six dogs were infected experimentally by the i.v. route and were monitored for 1 year. Clinical, immunological (humoral and cellular response) and parasitological (parasitaemia) parameters were evaluated monthly. Four dogs developed clinico-pathological signs compatible with leishmaniasis, whereas two dogs showed few abnormalities during the study. Evaluation of clinical, immunological and parasitological parameters showed that the intensity of Leishmania infection in blood samples, as indicated by the amount of Leishmania DNA, was correlated significantly with IgG, IgG1, IgG2, IgA, and IgM concentrations and with clinical signs. Parasitaemia and Leishmania-specific cell-mediated immunity were inversely correlated. Moreover, higher quantities of Leishmania DNA were detected in the liver, spleen, lymph node, skin and bone marrow of dogs exhibiting clinical signs than those exhibiting few such signs. These findings suggest that progressive disease in experimental canine leishmaniasis is associated with specific T-cell unresponsiveness and unprotective humoral responses which allow the dissemination and multiplication of L. infantum in different tissues.

Studies on the CPA cysteine peptidase in the Leishmania infantum genome strain JPCM5

Background

Visceral leishmaniasis caused by members of the Leishmania donovani complex is often fatal in the absence of treatment. Research has been hampered by the lack of good laboratory models and tools for genetic manipulation. In this study, we have characterised a L. infantum line (JPCM5) that was isolated from a naturally infected dog and then cloned. We found that JPCM5 has attributes that make it an excellent laboratory model; different stages of the parasite life cycle can be studied in vitro, it is accessible to genetic manipulation and it has retained its virulence. Furthermore, the L. infantum JPCM5 genome has now been fully sequenced.

Results

We have further focused our studies on LiCPA, the L. infantum homologue to L. mexicana cysteine peptidase CPA. LiCPA was found to share a high percentage of amino acid identity with CPA proteins of other Leishmania species. Two independent LiCPA-deficient promastigote clones (ΔLicpa) were generated and their phenotype characterised. In contrast to L. mexicana CPA-deficient mutants, both clones of ΔLicpa were found to have significantly reduced virulence in vitro and in vivo. Re-expression of just one LiCPA allele (giving ΔLicpa::CPA) was sufficient to complement the reduced infectivity of both ΔLicpa mutants for human macrophages, which confirms the importance of LiCPA for L. infantum virulence. In contrast, in vivo experiments did not show any virulence recovery of the re-expressor clone ΔLicpaC1::CPA compared with the CPA-deficient mutant ΔLicpaC1.

Conclusion

The data suggest that CPA is not essential for replication of L. infantum promastigotes, but is important for the host-parasite interaction. Further studies will be necessary to elucidate the precise roles that LiCPA plays and why the re-expression of LiCPA in the ΔLicpa mutants complemented the gene deletion phenotype only in in vitro and not in in vivo infection of hamsters.