Canine leishmaniasis transmission: higher infectivity amongst naturally infected dogs to sand flies is associated with lower proportions of T helper cells

Protective vaccination against murine visceral leishmaniasis using aldehyde-containing Quillaja saponaria sapogenins

The presence of aldehyde groups at C-23 and C-24 of the triterpen aglycon moiety was disclosed in 1H NMR spectra of both the Riedel de Haen saponin (R) (delta 9.336) and Quillaja saponaria QuilA saponin (delta 9.348). The sign of the C-28 acylated linked moiety (delta 176) was present in both saponins, while the delta 171 at C-28 (carboxy group) corresponding to the deacylated saponin, was only detected in the QuilA preparation, indicating 50% of hydrolysis of the ester moiety, probably due to the storage in aqueous solution. The normoterpen moiety was present in both saponins (signals at delta 14-18). The chemical removal of saponin glicidic moieties gave rise to their sapogenin fractions. Their 1H NMR spectra showed the presence of two signals (delta 9.226 and 9.236) for sapogenin R and two signals (delta 9.338 and 9.352) for the QuilA sapogenin. The intensity of the signals suggested two conformational isomers of sapogenin R in the ratio 53% of equatorial aldehyde group to 47% of axial aldehyde group, and two conformational isomers of QuilA sapogenin in the ratio 76% of equatorial aldehyde group to 24% of axial aldehyde group. The chemical treatment abolished the saponin slight in vivo toxicity, reduced their hemolytic potential, did not affect their aldehyde contents, but gave rise to an enriched axial aldehyde-containing sapogenin R with enhanced potential on antibody humoral response (anti-IgM, IgG, IgG1, IgG2a, IgG2b and IgG3) and to an enriched equatorial aldehyde-containing QuilA-sapogenin that induced a mainly cellular specific immune response (increased intradermal response to leishmanial antigen and IFNgamma sera levels) and effective protection against murine infection by L. donovani (77% reduction in liver parasitic load). Our results suggest that the Riedel de Haen saponin is probably a Quillaja saponaria saponin.

Immunotherapy against murine experimental visceral leishmaniasis with the FML-vaccine

The fucose mannose ligand (Leishmania donovani FML)-saponin vaccine has earlier shown its immunoprophylactic potential against visceral leishmaniasis in the CB hamster (87.7% of parasite load reduction), Balb/c (84.4%) and Swiss albino mouse (85-93%) models. In this investigation its specific immunotherapeutic efficacy against L. donovani infection in Balb/c mice was studied. The effects of vaccine treatment on the humoral response, delayed type of hypersensitivity to promastigote lysate (DTH), cytokine levels in sera and reduction of the liver parasitic load of L. donovani infected mice, were examined. The types and subtypes of anti-FML antibodies increased significantly in the vaccinees over the saline and saponin controls. As expected for a saponin vaccine, the highest ratios were found in relation to IgG1, IgG2a and IgG2b (4.4, 5 and 2.5, respectively). The DTH response and the in vitro ganglion cell proliferative response against FML antigen were also significantly higher than controls (P<0.005). Concomitantly, an impressive and specific decrease of liver parasitic burden was detected only in vaccine-treated animals (94.7%). Our results indicate that the therapeutic FML-vaccine has a potent effect on modulation of the murine infection leading to the reduction of parasitic load and signs of disease, being a new potential tool in the therapy and control of visceral leishmaniasis.

Domestic dog ownership: a risk factor for human infection with Leishmania (Viannia) species

An epidemiological study has shown that cumulative, village prevalence of Leishmania (Viannia) infection in dogs ranges from 8% to 45% in Huánuco, Peru. Using data from a prospective survey of human American cutaneous leishmaniasis (ACL) collected during 1994-98, it was shown that the village-level risk of human ACL did not significantly increase with dog abundance, neither in absolute terms (P = 0.659) nor in relation to dog:human ratios (P = 0.213). A significant positive association was observed between risk of human ACL and village dog ACL prevalence (P = 0.022). When controlled for village dog ACL prevalence, there also was an association between the average number of dogs per household and risk of human ACL (P = 0.033). The results suggest that dogs play a role in the (peri)domestic transmission of Le. (Viannia) to humans in Huánuco and indicate that a control intervention targeting dogs to control human ACL is warranted.

Canine Leishmaniasis

Canine leishmaniasis is caused by Leishmania infantum (syn. L. chagasi, in America) and is transmitted by the bite of phlebotomine sand flies. Infected dogs constitute the main domestic reservoir of the parasite and play a key role in transmission to humans, in which the parasite produces visceral leishmaniasis. The increasing awareness that control of the human disease depends on effective control of canine leishmaniasis has promoted, in the last few years, research into leishmanial infection in dogs. Newly available specific reagents and molecular tools have been applied to the detailed investigation of canine leishmaniasis and important advances have been made in elucidating the epidemiology and pathology of the disease. These new findings have led to better understanding of the disease, and have also helped in the development of new diagnostic methods and control measures against the infection, such as insecticide-impregnated collars for dogs, new drugs and treatment protocols, and second generation vaccines, with the hope of not only reducing the heavy burden of the disease among dogs but also reducing the incidence of human visceral leishmaniasis.

IgG1/IgG2 antibody dichotomy in sera of vaccinated or naturally infected dogs with visceral leishmaniosis

Canine antibody IgG, IgG1 and IgG2 anti-FML responses were investigated in dogs vaccinated with the fucose-mannose ligand (FML)-vaccine of Leishmania donovani and in dogs with naturally acquired visceral leishmaniosis. While similar levels of total IgG antibodies were seen in the seropositive naturally infected dogs and in vaccinees, significant differences between the groups were found regarding their IgG1/IgG2 anti-FML antibody composition (P<0.005). Higher IgG1 absorbencies were seen in infected dogs, while the IgG2 subtype was predominant in pre-immune sera, and in vaccinated animals, both after the first and the third dose (P<0.005). The average ratio between IgG1/IgG2 was then 1.124 for infected animals and 0.733 for FML-vaccinees. Also, a significant increase in IgG2 antibodies was observed from the first to the third vaccine injection (P<0.005). In the infected dogs, a high correlation between their IgG absorbance (Abs) values and the number of symptoms (P=0.017) was disclosed. Thus, the analysis of IgG subclasses disclosed a dichotomous response to visceral leishmaniosis: IgG1 associated to natural infection and IgG2 associated to a humoral response subsequent to the FML-vaccine treatment. An IgG1/IgG2>or=1 would characterize the sera of visceral leishmaniasis infected animals evoluting towards the overt disease while ratios <or=1 would characterize the sera response of vaccinated protected dogs.

Evaluation of a specific immunochemotherapy for the treatment of canine visceral leishmaniasis

The efficacy of specific immunochemotherapy against Leishmania infantum infection in dog was studied. The effects on transmission of the disease, as well as the cellular and humoral immune response were examined. The treated animals showed a significant reduction in the infection rates that were detected in Phlebotomus perniciosus females fed on the dog. The humoral immune response, assayed with an indirect immunofluorescence antibody test (IFAT), did not show significant variations under the influence of the therapy. The characterisation of the peripheral blood mononuclear cells (PBMC) using flow cytometry indicated a significant increase in the proportion of T lymphocytes, especially of CD4/TcR(alpha)(beta)(+) and CD4/CD45RA(+) cells, without showing evidence for modifications in the other leukocyte subsets. Cellular lymphoproliferation studies indicated a lack of a specific response to soluble leishmanial antigen (SLA), but the non-specific lymphoproliferative capacity assayed with phytohemagglutinin (PHA) was maintained.

Canine leishmaniasis: epidemiological risk and the experimental model

Increasing risk factors are making zoonotic visceral leishmaniasis a growing public health concern in many countries. Domestic dogs constitute the main reservoir of Leishmania infantum and Leishmania chagasi, and play a key role in the transmission to humans. New reagents and tools allow the detailed investigation of canine leishmaniasis, permitting the monitoring of the immunological status of dogs in both natural and experimental infections. Such studies are essential to determine the basis of the canine protective immune response and to establish a laboratory model, a significant aspect for the development of vaccines against canine leishmaniasis.

Molecular epidemiology of Leishmania infantum on the island of Majorca: a comparison of phenotypic and genotypic tools

In the Mediterranean basin, Leishmania infantum is the causative agent of both visceral and cutaneous leishmaniasis, and is an important opportunistic parasite in patients infected with human immunodeficiency virus (HIV). The commonest method used to study the variability of Leishmania spp. is isoenzyme analysis. In addition to this, we employed 3 assays based on the polymerase chain reaction (PCR): random amplified polymorphic deoxyribonucleic acid (RAPD), intergenic region typing (IRT), based on the amplification of ribosomal ribonucleic acid internal transcribed spacers and restriction fragment length polymorphism (PCR-RFLP). We used 54 L. infantum stocks isolated from HIV co-infected patients, 38 isolated from dogs, 3 isolated from immunocompetent patients and 3 isolated from 1826 sand files in the island of Majorca (Spain), a closed ecological niche. Zymodemes MON-1 (70%), MON-24 (11%) and MON-34 (18%) were found among the human isolates, and MON-1 (95%) and MON-108 (5%) among those from dogs. RAPD and IRT could not discriminate among the strains as they all gave the same pattern, even when different zymodemes were examined. In contrast, PCR-RFLP was able to distinguish the strains and, furthermore, a dendrogram (unweighted pair group method with arithmetic average [UPGMA]) was constructed from the genetic distances derived from RFLP data. The Leishmania isolates from HIV-infected subjects formed a single cluster, supporting the existence of an artificial anthroponotic cycle previously proposed by our group, in which syringes have been substituted for sand flies, and in which certain clones have been spread among intravenous drug users. This contrasts with the clusters representing a zoonotic cycle, involving dogs, sand flies and both immunocompetent and immunocompromised humans.