Decreased sensitivity to meglumine antimoniate (Glucantime) of Leishmania infantum isolated from dogs after several courses of drug treatment

Treatment of Leishmania infantum Infections in Dogs

Dogs are reservoir hosts of the zoonotic parasite Leishmania infantum, the causative agent of canine leishmaniosis. Antiparasitic drugs that are commonly used in dogs include allopurinol, miltefosine, and meglumine antimoniate. Treatment success is characterized by an improvement of disease signs, reduction in parasite load, as well as prevention of relapse. However, despite treatment, infections in dogs can usually not be cleared and often lead to (recurrent) signs of disease. Since most of the drugs used in dogs are also applied in human medicine, the prevention of treatment-induced drug-resistant Leishmania strains is a major one-health concern. This review article provides an overview of current treatment options for Leishmania-infected dogs with allopurinol, meglumine antimoniate, and miltefosine, related adverse effects, and drug resistance potential.

Validation of an improved reference freeze-dried direct agglutination test for detecting leishmaniasis in the canine reservoir

Introduction. Proper identification and management of post-kala-azar dermal leishmaniasis (PKDL) and canine leishmaniasis (CanL) cases are among the prerequisites to the effective control of visceral leishmaniasis worldwide. Unlike PKDL, CanL still awaits effective improvement because of its cryptic nature, absence of Leishmania parasites in lesions or lymph nodes and not complete sensitivity of some diagnostic tools in use. Because of the need for certain skills and equipment, both the liquid direct agglutination test and freeze-dried direct agglutination test (FD-DAT) versions are, in comparison with the indirect immunofluorescence antibody test (IFAT) or enzyme-linked immunosorbent assay (ELISA), practical and feasible diagnostic alternatives. Aim. Validate the performance of an improved FD-DAT to suit routine and large-scale applications in CanL endemic areas. Methodology. Introducing citrate-saline formaldehyde (CSF) as an anti-clumping agent to replace normal saline for antigen reconstitution and drastically, however, eligibly lower the concentration of promastigotes (1.4×107) in comparison with the original FD-DAT reference (>5×107 ml-1). To ensure optimal safety, β-mercaptoethanol was replaced by urea or SDS as a serum-reducing agent. Results. By improving the procedure for reconstitution of FD-DAT antigen with CSF, a 150% reduction in the test application cost was achieved. Expired test batches (±4 years earlier) were successfully revitalized to full validity. As compared to the 48 h shelf-life time for the original, an FD-DAT batch reconstituted here with CSF maintained stability for ±12 months. Conclusions. The highly concordant results with IFAT and ELISA (one-way ANOVA test, P=0.142, homogeneity of variances P=0.009) as routine CanL diagnostics further motivate the application of the improved FD-DAT for the detection of the disease in endemic areas.

Evidence for in vivo resistance against allopurinol in a dog infected with Leishmania infantum by reduction in copy numbers of the S-adenosylmethionine synthetase (METK) gene

BACKGROUND

In Europe, canine leishmaniasis is commonly caused by Leishmania infantum. Allopurinol is the main drug for long-term management of the disease, and clinical relapses of L. infantum infection treated with this drug are described. Resistance to allopurinol has been demonstrated in-vitro, but there is only little knowledge on in vivo resistance in dogs.

FINDINGS

A two-year-old female spayed Akita Inu that was adopted from a breeding facility near Nice in France was initially diagnosed with primary immune-mediated hemolytic anemia. Immunosuppressive treatment was initiated, and the dog was referred for a second opinion to the Clinique Veterinaire Alliance in France. PCR testing for L. infantum was performed out of EDTA blood and IFA as well as ELISA testing out of serum. Resistance to allopurinol was associated with chromosome and gene copy number (CN) variations including a decrease in the S-adenosylmethionine synthetase (METK) gene CN.

RESULTS

The dog showed pale mucous membranes, fever (39.1 °C), and a relapse of the anemia. The diagnosis of leishmaniasis was based on the cytological finding of Leishmania amastigotes (bone marrow, spleen, liver), positive PCR testing, and positive IFAT serology. The dog was treated with allopurinol over a period of 1316 days and additionally received two cycles of Glucantime® (meglumine antimoniate), before samples were submitted to the LABOKLIN laboratory to test for resistance against allopurinol. The laboratory work-up revealed mild thrombocytopenia, mild hyperproteinemia with hyperglobulinemia, a marked elevation of the c-reactive protein, and decreased iron concentration. Serum protein electrophoresis showed a polyclonal peak in the gamma globulins. Serology was positive in both ELISA (21.5 LE) and IFAT (1:1024). Quantitative PCR testing of blood was positive with low numbers of Leishmania (10/ml blood) at the timepoint of suspicion for resistance. The urinary protein-to-creatinine ratio was markedly elevated (2.5) and xanthine crystalluria was detected. A CN level of below 3 is considered suspicious for resistance, as revealed in the described Akita Inu dog.

CONCLUSIONS

Relapse of L. infantum infection after applying allopurinol for 1316 days due to resistance was suspected clinically. Positive PCR testing, consistent hematological and biochemistry abnormalities, and reduction in the METK gene CN backed up the clinical suspicion of resistance. Dogs infected with allopurinol resistant strains of L. infantum may represent a great risk for infection of naïve dogs, cats, and humans.

Effectiveness of an O-Alkyl Hydroxamate in Dogs with Naturally Acquired Canine Leishmaniosis: An Exploratory Clinical Trial

Canine leishmaniosis is a challenge in veterinary medicine and no drug to date has achieved parasite clearance in dogs. Histone deacetylase inhibitors are a drug class widely used in cancer chemotherapy. We have successfully used O-alkyl hydroxamates (vorinostat derivatives) in the treatment of a laboratory model of visceral leishmaniasis without showing toxicity. In order to test the effectiveness of a particular compound, MTC-305, a parallel-group, randomized, single-centre, exploratory study was designed in naturally infected dogs. In this clinical trial, 18 dogs were allocated into 3 groups and were treated with either meglumine antimoniate (104 mg Sb^V/kg), MTC-305 (3.75 mg/kg) or a combination of both using a lower MTC-305 dose (1.5 mg/kg) through a subcutaneous route for 2 treatment courses of 30 days, separated by a 30-day rest period. After treatment, a follow-up time of 4 months was established. Parasite burden in bone marrow, lymph node and peripheral blood were quantified through qPCR. Antibody titres were determined through an immunofluorescence antibody test, and cytokine expression values were calculated through RT-qPCR. Treatment safety was evaluated through the assessment of haematological and biochemical parameters in blood, weight, and gastrointestinal alterations. Assessment was carried out before, between and after treatment series. Treatment with MTC-305 was effective at reducing parasite burdens and improving the animals' clinical picture. Dogs treated with this compound did not present significant toxicity signs. These results were superior to those obtained using the reference drug, meglumine antimoniate, in monotherapy. These results would support a broader clinical trial, optimised dosage, and an expanded follow-up stage to confirm the efficacy of this drug.

Canine Leishmaniasis: Update on Epidemiology, Diagnosis, Treatment, and Prevention

Dog are the main reservoir of Leishmania infantum, causing canine leishmaniasis, an incurable multisystemic disease that leads to death in symptomatic dogs, when not treated. This parasite causes visceral, cutaneous, and mucosal leishmaniasis in people in the Mediterranean Basin, North Africa, South America, and West Asia. This disease is mostly unknown by veterinarians outside the endemic areas, but the disease is expanding in the Northern Hemisphere due to travel and climate change. New methodologies to study the epidemiology of the disease have found new hosts of leishmaniasis and drawn a completely new picture of the parasite biological cycle. Canine leishmaniasis diagnosis has evolved over the years through the analysis of new samples using novel molecular techniques. Given the neglected nature of leishmaniasis, progress in drug discovery is slow, and the few drugs that reach clinical stages in humans are unlikely to be commercialised for dogs, but several approaches have been developed to support chemotherapy. New-generation vaccines developed during the last decade are now widely used, along with novel prevention strategies. The implications of the epidemiology, diagnosis, treatment, and prevention of canine leishmaniasis are fundamental to public health.

In Vitro Reduced Susceptibility to Pentavalent Antimonials of a Leishmania infantum Isolate from a Human Cutaneous Leishmaniasis Case in Central Italy

Cutaneous leishmaniasis (CL) caused by Leishmania (Leishmania) infantum is endemic in the Mediterranean basin. Here we report an autochthonous case of CL in a patient living in central Italy with an unsatisfactory response to treatment with intralesional Meglumine Antimoniate and in vitro demonstration of reduced susceptibility to SbIII. Parasitological diagnosis was first achieved by histopathology on tissue biopsy and the patient was treated with a local infiltration of Meglumine Antimoniate. Since the clinical response at 12 weeks from the treatment's onset was deemed unsatisfactory, two further skin biopsies were taken for histopathological examination, DNA extraction and parasite isolation. L. (L.) infantum was identified by molecular typing. The low susceptibility to Meglumine Antimoniate was confirmed in vitro: the promastigotes from the patient strain showed significantly lower susceptibility to SbIII (the active trivalent form of antimonial) compared to the reference strain MHOM/TN/80/IPT1. The patient underwent a new treatment course with intravenous liposomal Amphotericin B, reaching complete healing of the lesion. Additional studies are needed to confirm the epidemiological and clinical relevance of reduced susceptibility to SbIII of human L. (L.) infantum isolate in Italy.

Scientometric analysis of chemotherapy of canine leishmaniasis (2000-2020)

Background

Zoonotic visceral leishmaniasis by Leishmania infantum is a first-order pathology in canine veterinary clinics in endemic areas. Moreover, canine infections are considered the main reservoir for human disease; despite their importance in the control of the disease within a One Health approach, no scientometric study has been published. Aims of the study included analyzing the impact of canine leishmaniasis (CanL) on the scientific literature, drugs or combinations used, trends in the period from 2000 to 2020 and efficacy criteria employed.

Methods

A Web of Science (WOS)-based analysis of publications on CanL and chemotherapy of the disease in the period 2000–2020 was carried out using a stepwise methodology. Data were analyzed by year, geographical origin, chemical groups, drugs and combinations, and efficacy criteria.

Results

Reports on CanL (n = 3324) represented < 16% of all publications on leishmaniasis (n = 20,968), and of these around 18% (n = 596) were related to chemotherapy. Publication records on CanL followed the distribution of the infection by L. infantum in endemic areas although Mediterranean countries were overrepresented in the reports on chemotherapy of CanL. Publications on the main antileishmanial drugs used in clinical practice showed a sustained tendency in the period analyzed. Pentavalent antimonials (Sb^V), alone or in combination with allopurinol, represented > 50% of all publications on chemotherapy of CanL despite the availability of more recently marketed drugs.

Conclusions

Chemotherapy of CanL still relies on Sb^V and combinations and to a lesser extent on miltefosine (MIL). Reports on chemotherapy are scarce and mostly publicly funded, and the variability of experimental conditions hampers the direct comparison of the efficacy of drugs, combinations and schedules. The vast majority of reports on efficacy do not include any information on supportive therapy; this reduces the actual value of the studies if intended for the practical management of the disease. Complete reports on the chemotherapy (etiological + symptomatic) would add value to the trials performed.

Treatment Failure in Cutaneous Leishmaniasis Patients Referred to the School of Public Health, Tehran University of Medical Sciences during 2008-2017

BACKGROUND

Cutaneous leishmaniasis (CL) is a vector borne disease predominantly found in tropical and subtropical countries, including Iran. For more than 6 decades, pentavalent antimonials have been used successfully worldwide for the treatment of leishmaniasis, but over the past few years, clinical resistance to these medications has increased. In this study, we evaluated CL patients who did not show any desirable responses to the anti-leishmanial treatment within a 10-year period (2008 to 2017).

METHODS

All patients from different parts of Iran suspected of having cutaneous leishmaniasis, who were referred to the laboratory of leishmaniosis in Tehran University of Medical Sciences from 2008-2017 were parasitological examined.

RESULTS

During this period, a total of 1480 suspected CL patients were referred to the laboratory of leishmaniosis. Samples from 655 patients (70.8%) suspected of having CL were positive microscopically. The failure rate in patients treated with anti-leishmaniasis medications for a minimum of three complete treatment periods was 1.83% (12 cases). There was no association between the number and size of skin lesions and patient characteristics. Also, the route of drug administration had no significant effect on the number and size of lesions.

CONCLUSION

In the present study, treatment failure was found in some confirmed CL patients treated with meglumine antimoniate. Over the past few years, it seems that had been increased in resistance to these medications. So, a review of the correct implementation of the treatment protocol and/or a combination therapy may be helpful in preventing an increase in the rate of treatment failure.

Nuclear and mitochondrial genome sequencing of North-African Leishmania infantum isolates from cured and relapsed visceral leishmaniasis patients reveals variations correlating with geography and phenotype

Although several studies have investigated genetic diversity of Leishmania infantum in North Africa, genome-wide analyses are lacking. Here, we conducted comparative analyses of nuclear and mitochondrial genomes of seven L. infantum isolates from Tunisia with the aim to gain insight into factors that drive genomic and phenotypic adaptation. Isolates were from cured (n=4) and recurrent (n=3) visceral leishmaniasis (VL) cases, originating from northern (n=2) and central (n=5) Tunisia, where respectively stable and emerging VL foci are observed. All isolates from relapsed patients were from Kairouan governorate (Centre); one showing resistance to the anti-leishmanial drug Meglumine antimoniate. Nuclear genome diversity of the isolates was analysed by comparison to the L. infantum JPCM5 reference genome. Kinetoplast maxi and minicircle sequences (1 and 59, respectively) were extracted from unmapped reads and identified by blast analysis against public data sets. The genome variation analysis grouped together isolates from the same geographical origins. Strains from the North were very different from the reference showing more than 34 587 specific single nucleotide variants, with one isolate representing a full genetic hybrid as judged by variant frequency. Composition of minicircle classes within isolates corroborated this geographical population structure. Read depth analysis revealed several significant gene copy number variations correlating with either geographical origin (amastin and Hsp33 genes) or relapse (CLN3 gene). However, no specific gene copy number variation was found in the drug-resistant isolate. In contrast, resistance was associated with a specific minicircle pattern suggesting Leishmania mitochondrial DNA as a potential novel source for biomarker discovery.

A randomized, blinded, controlled clinical trial comparing the efficacy of aminosidine (paromomycin)-allopurinol combination with the efficacy of meglumine antimoniate-allopurinol combination for the treatment of canine leishmaniosis due to Leishmania infantum

The aim of this 6-month, randomized, blinded, controlled clinical trial was to compare the efficacy and safety of aminosidine-allopurinol combination with that of meglumine antimoniate-allopurinol combination for the treatment of leishmaniosis in dogs without stage III or IV chronic kidney disease. Forty client-owned dogs were randomly assigned to group A [n = 20; aminosidine (15 mg/kg, subcutaneously, once daily, for 28 days) and allopurinol (10 mg/kg, per os, twice daily, for 6 months)] or group B [(n = 20; meglumine antimoniate (100 mg/kg SC, once daily, for 28 days) and allopurinol (10 mg/kg, per os, twice daily, for 6 months)]. Clinical and clinicopathological evaluations, parasitic load measurement (lymph node and bone marrow microscopy, bone marrow real-time PCR), specific serology and leishmanin skin test (LST) were performed at baseline (time 1) and after 14 (time 2), 28 (time 3), 60 (time 4) and 180 (time 5) days. Both treatments were safe and resulted in significant clinical and clinicopathological improvement, reduction of parasitic load and of indirect immunofluorescence antibody test (IFAT) titer and induction of positive LST. There was no significant difference between groups with regards to the primary outcome measures of the trial that included the proportion of dogs that presented severe treatment-related side effects, were cured and were parasitologically negative at time 5. However, some (proportion of dogs that presented no clinical signs, no hyperglobulinemia and negative serology at time 5) secondary outcome measures showed significant differences in favor of the meglumine antimoniate-allopurinol treatment arm. Treatment-related death occurred in one dog in each group, while injection site reactions appeared at a similar frequency in both groups. Due to the differences in some secondary outcome measures in association with the low power of this trial, it cannot be definitively concluded that the two treatments are equally effective. Therefore, the aminisodine-allopurinol combination cannot be proposed as a first-line treatment of CanL but rather as a second-line treatment that may be particularly useful to avoid repeated administration of meglumine antimoniate and in countries where the latter is not available or registered.

Clinical and Immunological Response in Dogs Naturally Infected by L. infantum Treated with a Nutritional Supplement

Simple Summary

We evaluated the effects of a commercial nutraceutical supplementation in dogs naturally affected by Leishmania infantum. This nutraceutical supplement is proposed to be added to dog diet to foster physiological immune-response during chronic leishmaniasis. Parasite clearance is infrequently obtained by immune response in both the human and canine leishmaniasis. Pharmacological therapies frequently fail in the elimination of L. infantum that could have settled in deep organs, escaping immune responses and therapy. The conventional drug therapy improves clinical signs, reduces parasitemia as well as relapse of infection. This nutraceutical supplementation can improve the impaired immune response of the infected dogs to fight the disease.

Abstract

The use of nutraceuticals as immunomodulators in the treatment of visceral leishmaniasis has generated interest in the current approaches to treat the disease. In this clinical and immunological study, we investigated whether the administration of a nutritional supplement mediates the immune-modulatory response in canine leishmaniosis (CL) and improves the clinical outcome of the disease. With this purpose, we analysed T lymphocyte subsets in peripheral blood (PB) of 12 dogs naturally infected by Leishmania infantum, following treatment with a nutritional supplement. The regulatory T (Treg) cells and the T helper (Th) 1 population were specifically evaluated. The animals underwent complete clinical examination and blood sample collection for haematological, biochemical, serological and immunological analysis before treatment (T0), one month (T30) and 3 months (T90) after the onset of the nutraceutical supplementation. We observed that nutraceutical supplementation was associated with immunomodulation of Th1 response and significant clinical improvement of the animals. No side effects were observed. Therefore, a potential supportive role for the nutraceutical supplement during canine leishmaniasis is proposed.

Effectiveness of the sesquiterpene (-)-α-bisabolol in dogs with naturally acquired canine leishmaniosis: an exploratory clinical trial

The use of natural products is a promising approach for treating visceral leishmaniosis. (-)-α-Bisabolol is a sesquiterpene that have been proved active in vivo on Leishmania infantum-infected mice without showing toxicity. A single-centre, parallel-group, randomized, exploratory study was designed to assess its efficacy in a canine leishmaniosis model involving naturally infected dogs. In this clinical trial, 12 dogs were allocated into two groups and were treated with either meglumine antimoniate (100 mg/kg) through subcutaneous route or (-)-α-bisabolol (30 mg/kg) through oral route for two treatment series of 30 days, separated by a 30-day interval. A 4-month follow-up period was established as well. Parasite loads in bone marrow, lymph node and blood were estimated through quantitative PCR. Antibody titres were determined through immunofluorescence antibody test and cytokine expression values were estimated through real-time reverse transcription-PCR. Treatment safety was assessed through the evaluation of weight, gastrointestinal alterations and hematological and biochemical parameters in blood. Analyses were performed before and after treatment, and after a 4-months follow-up period. Treatment with the sesquiterpene was effective at decreasing parasite loads and increasing gamma-interferon expression level. Dogs treated with (-)-α-bisabolol did not show any toxicity sign. These results were better than those obtained using the reference drug, meglumine antimoniate. The natural compound seemed to induce a Th1 immune response that led to parasitological and clinical improvement without showing any safety issue, suggesting a high potential for the treatment of canine and human visceral leishmaniosis.

Novel Areas for Prevention and Control of Canine Leishmaniosis

There have been multiple recent advances regarding tools for the control and prevention of canine leishmaniosis (CanL), including new preventative vaccines. In this review, these advances are evaluated based on control targets, including vector and parasite. Leishvet recommendations are provided for control practices based on the dog's risk of infection. New topical insecticide formulations have proven to be effective in preventing sand fly bites, and subsequently infection. Parasite control occurs through chemotherapeutic or immunologic means, which decrease or prevent transmission to other animals, including humans. Leishmaniosis control programs that include a combination of coordinated measures, either in individuals or for prevention across reservoir populations, are required.

Chemotherapy of leishmaniasis: present challenges

Cutaneous and visceral leishmaniasis are amongst the most devastating infectious diseases of our time, affecting millions of people worldwide. The treatment of these serious diseases rely on a few chemotherapeutic agents, most of which are of parenteral use and induce severe side-effects. Furthermore, rates of treatment failure are high and have been linked to drug resistance in some areas. Here, we reviewed data on current chemotherapy practice in leishmaniasis. Drug resistance and mechanisms of resistance are described as well as the prospects for applying drug combinations for leishmaniasis chemotherapy. It is clear that efforts for discovering new drugs applicable to leishmaniasis chemotherapy are essential. The main aspects on the various steps of drug discovery in the field are discussed.

Cross-resistance of Leishmania infantum isolates to nitric oxide from patients refractory to antimony treatment, and greater tolerance to antileishmanial responses by macrophages

Visceral leishmaniasis is a life-threatening disease characterized by intense parasitism of the spleen, liver, and bone marrow. Antimonials have served as front-line antileishmanial therapeutics for decades, but the increasing failure rates under antimonial treatment have challenged the continued use of these drugs. Pentavalent antimonials are known to reinforce the killing mechanisms of macrophages, although the associated mechanism remains unclear. Here, for the first time, we determined whether Leishmania infantum strains isolated from patients refractory to antimony treatment (relapse cases) were cross-resistant to antimonials, liposomal amphotericin B, and/or nitric oxide, and also whether these strains modulate macrophage infection. We selected four clinical isolates from relapse cases and two clinical isolates from antimony-responsive patients (control group) for the present study. The L. infantum promastigotes from all four relapse cases were resistant to trivalent antimonial treatment and nitric oxide, while only one isolate was resistant to liposomal amphotericin B. We evaluated whether the resistant strains from relapse cases showed enhanced infectivity and amastigote survival in macrophages, or macrophage-killing mechanisms in macrophages activated by lipopolysaccharide plus interferon gamma. Infection indexes calculated using macrophages infected with isolates from relapse were higher than those observed with control strains that were stimulated independently. Macrophage infection was higher with L. infantum isolates from relapse cases and correlated with enhanced interleukin 1-β production but showed similar nitrite production. Our results demonstrate that L. infantum field isolates from relapse cases were resistant to antimonials and nitric oxide and that these parasites stimulated inflammatory cytokines and were resistant to macrophage-killing mechanisms, factors that may contribute to disease severity.

Decreased antimony uptake and overexpression of genes of thiol metabolism are associated with drug resistance in a canine isolate of Leishmania infantum

Visceral leishmaniasis (VL) caused by the protozoan parasite Leishmania infantum, is one of the most important zoonotic diseases affecting dogs and humans in the Mediterranean area. The presence of infected dogs as the main reservoir host of L. infantum is regarded as the most significant risk for potential human infection. We have studied the susceptibility profile to antimony and other anti-leishmania drugs (amphotericin B, miltefosine, paromomycin) in Leishmania infantum isolates extracted from a dog before and after two therapeutic interventions with meglumine antimoniate (subcutaneous Glucantime^®, 100 mg/kg/day for 28 days). After the therapeutic intervention, these parasites were significantly less susceptible to antimony than pretreatment isolate, presenting a resistance index of 6-fold to Sb^III for promastigotes and >3-fold to Sb^III and 3-fold to Sb^V for intracellular amastigotes. The susceptibility profile of this resistant L. infantum line is related to a decreased antimony uptake due to lower aquaglyceroporin-1 expression levels. Additionally, other mechanisms including an increase in thiols and overexpression of enzymes involved in thiol metabolism, such as ornithine decarboxylase, trypanothione reductase, mitochondrial tryparedoxin and mitochondrial tryparedoxin peroxidase, could contribute to the resistance as antimony detoxification mechanisms. A major contribution of this study in a canine L. infantum isolate is to find an antimony-resistant mechanism similar to that previously described in other human clinical isolates.

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Antimony resistance in a Leishmania infantum line from a dog is reported.

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Resistance due to decrease antimony uptake by lower aquaglyceroporin-1 expression.

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An increase in thiols metabolism contribute to antimony resistance.

Allopurinol Resistance in Leishmania infantum from Dogs with Disease Relapse

BACKGROUND

Visceral leishmaniasis caused by the protozoan Leishmania infantum is a zoonotic, life threatening parasitic disease. Domestic dogs are the main peridomestic reservoir, and allopurinol is the most frequently used drug for the control of infection, alone or in combination with other drugs. Resistance of Leishmania strains from dogs to allopurinol has not been described before in clinical studies.

METHODOLOGY/PRINCIPAL FINDINGS

Following our observation of clinical disease relapse in dogs under allopurinol treatment, we tested susceptibility to allopurinol of L. infantum isolated from groups of dogs pre-treatment, treated in remission, and with disease relapse during treatment. Promastigote isolates obtained from four treated relapsed dogs (TR group) showed an average half maximal inhibitory concentration (IC50) of 996 μg/mL. A significantly lower IC50 (P = 0.01) was found for isolates from ten dogs before treatment (NT group, 200 μg/mL), as well as for five isolates obtained from treated dogs in remission (TA group, 268 μg/mL). Axenic amastigotes produced from isolates of the TR group also showed significantly higher (P = 0.002) IC50 compared to the NT group (1678 and 671 μg/mL, respectively). The lower sensitivity of intracellular amastigotes from the TR group relative to those from the NT group (P = 0.002) was confirmed using an infected macrophage model (6.3% and 20% growth inhibition, respectively at 300 μg/mL allopurinol).

CONCLUSIONS

This is the first study to demonstrate allopurinol resistance in L. infantum and to associate it with disease relapse in the canine host. These findings are of concern as allopurinol is the main drug used for long term control of the disease in dogs, and resistant L. infantum strains may enhance uncontrolled transmission to humans and to other dogs.

Transmission potential of antimony-resistant leishmania field isolates

We studied the development of antimony-resistant Leishmania infantum in natural vectors Lutzomyia longipalpis and Phlebotomus perniciosus to ascertain the risk of parasite transmission by sand flies. All three resistant strains produced fully mature late-stage infections in sand flies; moreover, the resistant phenotype was maintained after the passage through the vector. These results highlight the risk of circulation of resistant Leishmania strains and question the use of human drugs for treatment of dogs as Leishmania reservoirs.

Drug resistance in natural isolates of Leishmania donovani s.l. promastigotes is dependent of Pgp170 expression

Resistance of pathogens to drugs is a growing concern regarding many diseases. Parasites like Leishmania, Plasmodium and Entamoeba histolytica; and neoplastic cells, present the multidrug-resistant phenotype rendering chemotherapy ineffective. The acquired resistance of Leishmania to antimony has generated intense research on the mechanisms involved but the question has not yet been resolved. To test the hypothesis that drug efflux in Leishmania, as measured by flow cytometry using the fluorescent dye Rhodamine-123, is largely dependent on the number of efflux pumps an isolate can express, the amount of Pgp 170 molecules was assessed in ten field isolates (5 “resistant” and 5 “susceptible”) using: Western Blotting, Confocal and Transmission Electron Microscopy, and proteomics. Their survival after exposure to three antileishmanial drugs, in vitro, was evaluated and clinical data were compared to the in vitro results. All isolates were resistant to Glucantime but susceptible to Miltefosine, whilst Amphotericin B was more effective on the “susceptible” isolates. The MDR gene, expressing the transmembrane efflux pump Pgp 170, appears to play a key role in the phenomenon of drug resistance. When “susceptible” versus “resistant” parasites were compared, it was shown that the higher the number of Pgp 170 molecules the higher the Rhodamine-123 efflux from the parasite body and, when exposed to the drug, the number of efflux pumps increased. However, the rate of this increase was not linear and it is possible that there is a maximum number of Pgp 170 molecules an isolate can express. Nevertheless, the phenomenon is a complex one and other factors and proteins are involved in which the HSP-70 group proteins, detected in the “resistant” isolates, may play a significant role.

In vitro drug susceptibility of Leishmania infantum isolated from humans and dogs

Visceral leishmaniasis (VL) caused by parasites of Leishmania donovani complex is a severe human disease which often leads to death if left untreated. Domestic dogs are the main reservoir hosts for zoonotic human visceral infection caused by Leishmania infantum. In the absence of effective human and dog vaccines, the only feasible way to treat and control leishmaniasis is through the use of suitable medications. To know the drug susceptibility of human and canine Leishmania strains from Lisbon-Portugal, a study on a panel of strains was conducted by testing the susceptibility of promastigotes and intracellular amastigotes to the common drugs used in canine leishmaniasis (CanL) and human VL (meglumine antimoniate, amphotericin B, miltefosine and allopurinol). Although a high heterogeneity of susceptibilities was obtained to each drug on both axenic promastigote and intracellular amastigote assays, intracellular amastigotes system correlated better with treatment outcome. Parasites isolated from the refractory human case were the least susceptible to the drugs used highlighting that the emergence of cross-resistance to the drugs available for human therapy should not be neglected. Furthermore, parasites isolated from dogs showed low susceptibility to the main drugs used in CanL treatment. Our results focus the importance of reducing/avoiding the emergence and spread of resistant parasites in the canine and human populations, a factor that requires special consideration when dogs are treated using the same available anti-Leishmania drugs for human VL. In addition, efforts should be made in order to standardize the conditions used to test drug susceptibility (methodologies, drug formulations and media) in order to compare results between laboratories.

Antimony resistance and environment: Elusive links to explore during Leishmania life cycle

Leishmania drug resistance and particularly antimony resistance still continues to emerge in different part of the world. Because visceral and cutaneous leishmaniasis are transmitted in foci with zoonotic or anthroponotic life-cycles, the link between chemotherapeutic resistance and the selection for drug resistance, through drug consumption, cannot be as obvious for all forms of leishmaniasis. The underlying factors that trigger the selection of antimony resistant parasites are poorly studied in regard to environmental aspects. Recently, a correlation between the emergence of antimony unresponsiveness in India and water arsenic contamination has been raised. The presence of some yet unidentified environmental factors driving the selection of antimony resistant Leishmania populations in a zoonotic context of leishmaniasis is also currently questioned. The identification of key molecules involved in the selection of antimony resistance and their importance in the selective process have to be re-evaluated in light of the environment were all the hosts of Leishmania (mammalian and arthropod) evolved. These new insights will help to (i) address the risk of therapeutic failure associated with the emergence of drug-resistance and (ii) propose new therapeutic protocols to aim at reducing the risk of resistance in endemic areas.

Leishmania chagasi naturally resistant to nitric oxide isolated from humans and dogs with visceral leishmaniasis in Brazil

Nitric oxide (NO) plays an important role as a leishmanicidal agent in murine macrophages. NO resistant Escherichia coli and Mycobacterium tuberculosis have been associated with poor outcomes of their resulting diseases. NO resistant Leishmania braziliensis has also been identified and exacerbates the clinical course of human leishmaniasis. We report, for the first time, natural resistance of Leishmania chagasi promastigotes to NO. These parasites were isolated from humans and dogs with visceral leishmaniasis. We also demonstrate that this resistance profile was associated with a greater survival capacity and a greater parasite burden in murine macrophages, independent of activation and after activation by IFN-γ and LPS.

Antimony resistance in leishmania, focusing on experimental research

Leishmaniases are parasitic diseases that spread in many countries with a prevalence of 12 million cases. There are few available treatments and antimonials are still of major importance in the therapeutic strategies used in most endemic regions. However, resistance toward these compounds has recently emerged in areas where the replacement of these drugs is mainly limited by the cost of alternative molecules. In this paper, we reviewed the studies carried out on antimonial resistance in Leishmania. Several common limitations of these works are presented before prevalent approaches to evidence antimonial resistance are related. Afterwards, phenotypic determination of resistance is described, then confronted to clinical outcome. Finally, we detail molecular mechanisms and targets involved in resistance and already identified in vitro within selected mutant strains or in clinical isolates.

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.

Decreased effect of glucantime in cutaneous leishmaniasis complicated with secondary bacterial infection

Background:

Glucantime is regarded as the first-line treatment of cutaneous leishmaniasis (CL); however, failure to treatment is a problem in many cases.

Aim:

The aim was to evaluate the therapeutic effect of glucantime in CL complicated with secondary bacterial infection compared to uncomplicated lesions.

Methods:

This experimental study was performed in Skin Diseases and Leishmaniasis Research Center, Isfahan, Iran. A total of 161 patients enrolled in the study had CL confirmed by positive smear of lesions. All the patients were treated with systemic glucantime for 3 weeks and followed for 2 months. Response to treatment was defined as loss of infiltration, reepithelization, and negative smear. Depending on the results of bacterial cultures, the lesions were divided into two groups and the efficacy of glucantime was compared.

Results:

A total of 123 patients (76.4%) were negative, and 38 patients (23.6%) were positive for secondary bacterial infection. In groups with negative bacterial culture response to treatment was 65% (80 patients) and in the other positive group, it was 31.6% (12 patients), with a difference (χ² = 13.77, P < 0.01).

Conclusion:

Therapeutic effect of glucantime showed a decrease in CL lesions with secondary bacterial infection. Therefore, in the cases of unresponsiveness to treatment, the lesions should be evaluated for bacterial infection, before repeating the treatment.

Use of antimony in the treatment of leishmaniasis: current status and future directions

In the recent past the standard treatment of kala-azar involved the use of pentavalent antimonials Sb(V). Because of progressive rise in treatment failure to Sb(V) was limited its use in the treatment program in the Indian subcontinent. Until now the mechanism of action of Sb(V) is not very clear. Recent studies indicated that both parasite and hosts contribute to the antimony efflux mechanism. Interestingly, antimonials show strong immunostimulatory abilities as evident from the upregulation of transplantation antigens and enhanced T cell stimulating ability of normal antigen presenting cells when treated with Sb(V) in vitro. Recently, it has been shown that some of the peroxovanadium compounds have Sb(V)-resistance modifying ability in experimental infection with Sb(V) resistant Leishmania donovani isolates in murine model. Thus, vanadium compounds may be used in combination with Sb(V) in the treatment of Sb(V) resistance cases of kala-azar.

Successful treatment of Old World cutaneous leishmaniasis caused by Leishmania infantum with posaconazole

Old World cutaneous leishmaniasis is a widespread and potentially disfiguring protozoal infection that is endemic in the Mediterranean basin, Africa, and parts of Asia. Human infection is caused by several species of Leishmania parasites, such as Leishmania infantum. Available systemic and topical treatments vary in efficacy and are often unjustified due to their toxicity. We report on a case that was treated with posaconazole, a drug typically considered an antifungal agent but which also targets specific metabolic pathways of the parasite.

Frequency of drug resistance gene amplification in clinical leishmania strains

Experimental studies about Leishmania resistance to metal and antifolates have pointed out that gene amplification is one of the main mechanisms of drug detoxification. Amplified genes code for adenosine triphosphate-dependent transporters (multidrug resistance and P-glycoproteins P), enzymes involved in trypanothione pathway, particularly gamma glutamyl cysteine synthase, and others involved in folates metabolism, such as dihydrofolate reductase and pterine reductase. The aim of this study was to detect and quantify the amplification of these genes in clinical strains of visceral leishmaniasis agents: Leishmania infantum, L. donovani, and L. archibaldi. Relative quantification experiments by means of real-time polymerase chain reaction showed that multidrug resistance gene amplification is the more frequent event. For P-glycoproteins P and dihydrofolate reductase genes, level of amplification was comparable to the level observed after in vitro selection of resistant clones. Gene amplification is therefore a common phenomenon in wild strains concurring to Leishmania genomic plasticity. This finding, which corroborates results of experimental studies, supports a better understanding of metal resistance selection and spreading in endemic areas.

Multicentric, controlled clinical study to evaluate effectiveness and safety of miltefosine and allopurinol for canine leishmaniosis

The aim of this trial was to evaluate the effectiveness and safety of miltefosine-allopurinol combination therapy vs. the current reference combination therapy, meglumine antimoniate-allopurinol, for canine leishmaniosis. Dogs included in the study exhibited clinical signs of the disease, were positive by PCR and serologically positive by immunofluorescent antibody test for leishmaniosis, and negative for ehrlichiosis. Dogs were divided into two groups: Group 1 was treated with 2 mg/kg of miltefosine orally once daily for 28 days and 10 mg/kg of allopurinol orally twice daily for 7 months; Group 2 was treated with 50 mg/kg of meglumine antimoniate sub-cutaneously twice daily for 28 days and allopurinol (same dose as Group 1) for 7 months. Dogs were examined according to the following schedule: pre-inclusion, Day 0 (D0), D14, D28, D84, D140 and D196. At each visit, blood, urine and bone marrow samples were collected. Parameters monitored included haematology, biochemistry, protein electrophoresis, serology, urinary protein/creatinine ratio and RTQ-PCR performed on bone marrow aspirates. A significant reduction in total clinical score and parasite load was observed in both groups over the 7-month study period (P < 0.0001), with no significant difference between groups (P = 0.3). The safety of miltefosine-allopurinol combination therapy was confirmed by lack of effect on renal and hepatic parameters and adverse reactions. Miltefosine, in combination with allopurinol, offers a safe, convenient and effective alternative treatment option for canine leishmaniosis compared to the reference therapy.

Dynamics and predictive potential of antibodies against insect-derived recombinant Leishmania infantum proteins during chemotherapy of naturally infected dogs

A predictive marker for the success treatment of canine leishmaniasis is required for the application of a more rational therapy protocol, which must improve the probability of cure and reduce Leishmania resistance to drugs. We investigated the dynamics and predictive value of antibodies against insect-derived recombinant L. infantum proteins rKMPII and rTRYP by using an enzyme-linked immunosorbent assay with retrospective serum samples from 36 dogs during treatment of canine leishmaniasis. In the entire group of dogs, concentrations of antibodies against rKMPII and rTRYP significantly decreased earlier than concentrations of antibodies against crude total Leishmania antigen (one versus six months), which suggested that the dynamics of antibodies against recombinant proteins may be useful for assessing clinical improvement after treatment. Interestingly, decreases in antibody concentrations against rKMPII occurred earlier in disease-free dogs than in dogs that remain clinically ill one year after beginning of treatment, which suggested that these antibodies may be useful for predicting disease-free survival one year after the beginning of therapy against canine leishmaniasis.

Leishmania donovani s.l.: evaluation of the proliferation potential of promastigotes using CFSE staining and flow cytometry

Leishmania infantum causes visceral leishmaniasis in all countries in the Mediterranean basin. It uses Phlebotomine sandflies as vectors where the promastigote stage develops, reproduces and becomes infective. Therefore the reproductive power of the promastigotes determines the inoculum size of the isolate. Ten Leishmania strains from Cyprus: two Leishmania donovani and eight L. infantum were used to study the proliferation capacity of the promastigotes. Population increase during a 6-day culture period was assessed quantitatively, by haematocytometer enumeration, and qualitatively by following the division history of each population during the same period by CFSE staining and flow cytometry. The strains exhibited different proliferation rates with L. infantum showing higher multiplication rates than L. donovani. These differences may represent their fitness capabilities and their ability to synchronize the multiplication activity of individual members in the population for the production of a sizeable inoculum in time for the vector's blood meal.

Leishmania (Leishmania) infantum/chagasi: Histopathological aspects of the skin in naturally infected dogs in two endemic areas

In the New World, visceral leishmaniasis (VL), which is a progressive disease and frequently fatal, is caused by Leishmania (Leishmania) infantum/chagasi. It is endemic in many regions of Brazil and occasionally occurs in non-endemic regions when dogs from an endemic area are introduced. The aim of the present study is to compare different skin infection patterns of dogs from two leishmaniasis endemic areas. A histological analysis of dogs from Campo Grande, Mato Grosso do Sul state, a region where epidemic episodes are currently taking place, showed dermic inflammatory infiltrates, composed of numerous vacuolated parasitized macrophages, few lymphocytes, plasma cells and many degranulated mast cells. In the other region of the study, São Luís, Maranhão state, the skin of dogs presented a remarkable inflammatory reaction composed mainly of plasma cells, lymphocytes and very few parasites. We concluded that there is a difference in the skin lesion patterns of dogs with leishmaniasis that is directly related to the endemic area where the animals live.

Antibiotic resistance free plasmid DNA expressing LACK protein leads towards a protective Th1 response against Leishmania infantum infection

Canine visceral leishmaniasis is a serious public health concern in the Mediterranean basin since dogs are the main Leishmania infantum reservoir. However, there is not a vaccination method in veterinary use in this area, and therefore the development of a vaccine against this parasite is essential for the possible control of the disease. Previous reports have shown the efficacy of heterologous prime-boost vaccination with the pCIneo plasmid and the poxvirus VV (both Western Reserve and MVA strains) expressing L. infantum LACK antigen against canine leishmaniasis. As pCIneo-LACK plasmid contains antibiotic resistance genes, its use as a profilactic method is not recommended. Hence, the antibiotic resistance gene free pORT-LACK plasmid is a more suitable tool for its use as a vaccine. Here we report the protective and immunostimulatory effect of the prime-boost pORT-LACK/MVA-LACK vaccination tested in a canine experimental model. Vaccination induced a reduction in clinical signs and in parasite burden in the liver, an induction of the Leishmania-specific T cell activation, as well as an increase of the expression of Th1 type cytokines in PBMC and target organs.

Clinical efficacy and tolerance of miltefosine in the treatment of canine leishmaniosis

The study was aimed to assess the efficacy and tolerance profiles of an oral administration miltefosine drug (Milteforan(R), Virbac) in dogs with natural leishmaniosis. In this multicentric open trial, 96 dogs were treated with the drug administered orally at a dose of 2 mg/kg body weight once a day for 28 days. During the 56-day trial, clinical signs of the dogs were monitored every 2 weeks. On the first and the last visits, blood and bone marrow samples were collected for laboratory analyses. According to clinical scores, the treatment demonstrated a significant time-dependent therapeutic effect resulting in a 61.2% mean reduction on day 56. Hematologic and biochemical analyses showed improvements in most of the parameters examined, supporting the observed clinical efficacy of the drug. Overall, veterinarians estimated that 82.7% of the dogs treated with the miltefosine drug showed an equal or higher treatment efficacy than other antileishmanial drugs. During the trial, the adverse reactions probably associated with the drug treatment were observed in 11.7% of the dogs. However, they were not serious. The most frequent one was vomiting, which was transient, self-limiting, and reversible. These data demonstrate that the drug, at the recommended dose and treatment regime, was safe and efficacious for the treatment of canine leishmaniosis.

Comparative study on the short term efficacy and adverse effects of miltefosine and meglumine antimoniate in dogs with natural leishmaniosis

The aim of this study was to compare the efficacy and safety of oral administration of miltefosine (Milteforan) at 2 mg/kg/day for 28 days (Group M; n = 60) with a subcutaneous administration of meglumine antimoniate (Glucantime) at 50 mg/kg/12 h or at 100 mg/kg/day for 28 days (Group G; n = 59) in the treatment of canine leishmaniosis in dogs. Out of 119 dogs included in the study, 90 could be used for efficacy assessment and 112 for safety assessment. Treated dogs were followed up for 6 weeks, with re-checks every 14 days. The mean total clinical scores significantly decreased throughout the study in both treatment groups. The evolution of parasitological results after treatment (D42) shows a high percentage of dogs with negative bone marrow smears, 90% and 91.3% in groups M and G respectively, and did not significantly differ between groups (p = 0.8066). Out of the 112 dogs used for the safety assessment, only 26 dogs (23.2%) presented product-related adverse events concerning the gastrointestinal tract. These results showed that miltefosine at 2 mg/kg once daily can be safely used over a 28-day period in the treatment of canine leishmaniosis and provides both a steadily increasing improvement of the clinical signs and a good leishmanicidal efficacy.

Directions for the diagnosis, clinical staging, treatment and prevention of canine leishmaniosis

Canine leishmaniosis (CanL) due to Leishmania infantum is a life threatening zoonotic disease with a wide distribution in four continents and importance also in non-endemic regions. The purpose of this report is to present a consensus of opinions on the diagnosis, treatment, prognosis and prevention of CanL in order to standardize the management of this infection. CanL is a disease in which infection does not equal clinical illness due to the high prevalence of subclinical infection among endemic canine populations. The most useful diagnostic approaches include serology by quantitative techniques and PCR. High antibody levels are associated with severe parasitism and disease and are diagnostic of clinical leishmaniosis. However, the presence of lower antibody levels is not necessarily indicative of disease and further work-up is necessary to confirm CanL by other diagnostic methods such as cytology, histopathology and PCR. We propose a system of four clinical stages, based on clinical signs, clinicopathological abnormalities and serological status. Suitable therapy and expected prognosis are presented for each of the stages. The combination of meglumine antimoniate and allopurinol constitutes the first line pharmaceutical protocol. However, although most dogs recover clinically after therapy, complete elimination of the parasite is usually not achieved and infected dogs may eventually relapse. Follow-up of treated dogs with blood counts, serum biochemistry, urinalysis, serology and PCR is essential for prevention of relapses. Protection against sand fly bites by topical insecticides is effective in reducing infection, and recent development of vaccines has indicated that prevention by vaccination is feasible.

Use of domperidone in the treatment of canine visceral leishmaniasis: a clinical trial

The aim of this study was to evaluate the effects of domperidone, a dopamine D2 receptor antagonist, in dogs naturally infected by Leishmania infantum. Ninety-eight dogs were treated with single-agent domperidone at 1mg/kg twice a day orally for 1 month. Clinical, serological, biochemical and immunological examinations were conducted for the following 12 months. Domperidone was effective in controlling and reducing clinical signs and antibody titre. Significant decreases in reciprocal serum antibodies were seen in 74.3% of the dogs with mild clinical signs and 40% of the dogs became seronegative. In dogs with several clinical signs and high antibody titres, clinical improvement occurred in 86% of animals and the reciprocal serum antibody titres decreased in 38% of these dogs. A significant increase was noted in the immune cellular status, as measured by the leishmanin skin test and a lymphocyte proliferation assay.

Long-lasting protection against canine visceral leishmaniasis using the LiESAp-MDP vaccine in endemic areas of France: double-blind randomised efficacy field trial

Vaccination against visceral leishmaniasis has received limited attention compared with cutaneous leishmaniasis, although the need for an effective vaccine against visceral leishmaniasis is pressing. Dogs constitute the major reservoir of Leishmania infantum/chagasi responsible for human visceral leishmaniasis. We have recently demonstrated that the combination of naturally excreted/secreted antigens, easily purified from culture supernatant of Leishmania infantum promastigotes (LiESAp) as vaccine antigen in formulation with muramyl dipeptide (MDP) as adjuvant, conferred 100% protection to dogs experimentally infected with L. infantum by inducing in vaccinees a significant, stable and long-lasting Th1-type cell response [Lemesre JL, Holzmuller P, Cavaleyra M, Bras Gonçalves R, Hottin G, Papierok G. Protection against experimental visceral leishmaniasis infection in dogs immunised with purified excreted secreted antigens of L. infantum promastigotes. Vaccine 2005; 23:2825-2840; Holzmuller P, Cavaleyra M, Moreaux J, Kovacic R, Vincendeau P, Papierok G, Lemesre JL. Lymphocytes of dogs immunised with purified excreted secreted antigens of L. infantum co-incubated with Leishmania-infected macrophages produce IFN-gamma resulting in nitric oxide-mediated amastigote apoptosis. Vet. Immunol. Immunopathol. 2005, 106:247-257]. In this report, protection against visceral leishmaniasis is investigated in naturally exposed dogs of endemic areas of the South of France vaccinated with LiESAp/MDP vaccine. A double-blind randomised efficacy field trial was developed on a large-scale dog population composed of vaccinees (n=205) and placebo-treated animals (n=209), which were prospectively studied for a 2-year period. 0f the initial 414 enrolled dogs, 340 (175 controls and 165 vaccinees) were analysed for clinical, serological and parasitological studies at 24 months post-vaccination, after two sand fly seasons. Strong seroconversion disclosed by an L. infantum indirect immunofluorescence antibody test (IFAT) associated with suspicious clinical symptoms, considered an indication that the animals had an established progressive infection, was only observed in the placebo group. The seropositive and/or symptomatic dogs were selected for further examination for possible Leishmania infection by culturing parasites from bone-marrow aspirate. The presence of leishmanial infection was also evaluated by means of the PCR analysis of bone marrow samples in all enrolled dogs prior to vaccination and in all evaluated animals (175 controls and 165 vaccinees) at 24 months post-vaccination. After two transmission cycles completed, the Leishmania infection rate was 0.61% (1/165) in vaccinated dogs and 6.86% (12/175) in the placebo group. The efficacy of the vaccine was calculated to be 92% (P=0.002). A clear difference between the dogs that received vaccine and those that received placebo was also established by the results of their immune status. Increased anti-LiESAp IgG2 reactivity and significant enhanced NO-mediated anti-leishmanial activity of canine macrophages in response to higher IFN-gamma production by T cells were almost exclusively revealed in vaccinees. The LiESAp-MDP vaccine induced a significant, long-lasting and strong protective effect against canine visceral leishmaniasis in the field.

Leishmania spp.: proficiency of drug-resistant parasites

Leishmaniasis is a disease caused by at least 17 different species of protozoan Leishmania parasites and currently affects around 12 million people living mostly in tropical and subtropical areas. Failure to treat leishmaniasis successfully is often due to drug resistance. However, there are no cellular and molecular markers of chemoresistance against leishmanicidal drugs and the only reliable method for monitoring resistance of individual isolates is the in vitro amastigote/macrophage model. It is thus necessary to find cellular and molecular markers that can be used systematically to identify the drug-resistant phenotype of the infecting parasites. Until now, whether drug resistance in Leishmania compromises parasite proficiency, e.g. in terms of infectivity or metabolism, has not been systematically evaluated. Therefore, here we examine whether the physiological changes expressed by drug-resistant Leishmania reflect a modification of parasite vitality in drug-resistant compared with drug-sensitive parasites. Finally, the clinical implications of drug resistance in Leishmania are also discussed.

Canine Leishmaniasis Chemotherapy: Dog's Clinical Condition and Risk of Leishmania Transmission

The aim of this study was to investigate whether treatment against canine leishmaniasis reduced the presence of Leishmania in the healthy skin of dogs, affecting the capacity of parasite transmission. A total of 37 dogs from an endemic region of leishmaniasis were studied. Thirteen symptomatic animals revealed parasites in the bone marrow and eight had also in the skin. Five of the 22 dogs that had been treated with meglumine antimoniate alone, meglumine antimoniate or trifluralin followed by allopurinol or just with allopurinol had the parasite in bone marrow but none showed Leishmania in the skin. One dog that was treated only with aminosidine was polisymptomatic and had parasites in bone marrow and skin. The different treatments used in this study did not completely eliminate the parasite allowing relapses to occur when the treatment is discontinued, but the use of meglumine antimoniate or allopurinol, alone or combined may improve dogs clinical condition and reduce or eliminate the parasite from the skin decreasing the probability of Leishmania transmission.

Chemotherapy in the treatment and control of leishmaniasis

Drugs remain the most important tool for the treatment and control of both visceral and cutaneous leishmaniasis. Although there have been several advances in the past decade, with the introduction of new therapies by liposomal amphotericin, oral miltefosine and paromomycin (PM), these are not ideal drugs, and improved shorter duration, less toxic and cheaper therapies are required. Treatments for complex forms of leishmaniasis and HIV co-infections are inadequate. In addition, full deployment of drugs in treatment and control requires defined strategies, which can also prevent or delay the development of drug resistance.

Drug resistance in leishmaniasis

Leishmaniasis is a complex disease, with visceral and cutaneous manifestations, and is caused by over 15 different species of the protozoan parasite genus Leishmania. There are significant differences in the sensitivity of these species both to the standard drugs, for example, pentavalent antimonials and miltefosine, and those on clinical trial, for example, paromomycin. Over 60% of patients with visceral leishmaniasis in Bihar State, India, do not respond to treatment with pentavalent antimonials. This is now considered to be due to acquired resistance. Although this class of drugs has been used for over 60 years for leishmaniasis treatment, it is only in the past 2 years that the mechanisms of action and resistance have been identified, related to drug metabolism, thiol metabolism, and drug efflux. With the introduction of new therapies, including miltefosine in 2002 and paromomycin in 2005-2006, it is essential that there be a strategy to prevent the emergence of resistance to new drugs; combination therapy, monitoring of therapy, and improved diagnostics could play an essential role in this strategy.