Leishmania infantum xenodiagnosis from vertically infected dogs reveals significant skin tropism.

BACKGROUND: Dogs are the primary reservoir for human visceral leishmaniasis due to Leishmania infantum. Phlebotomine sand flies maintain zoonotic transmission of parasites between dogs and humans. A subset of dogs is infected transplacentally during gestation, but at what stage of the clinical spectrum vertically infected dogs contribute to the infected sand fly pool is unknown. METHODOLOGY/PRINCIPAL FINDINGS: We examined infectiousness of dogs vertically infected with L. infantum from multiple clinical states to the vector Lutzomyia longipalpis using xenodiagnosis and found that vertically infected dogs were infectious to sand flies at differing rates. Dogs with mild to moderate disease showed significantly higher transmission to the vector than dogs with subclinical or severe disease. We documented a substantial parasite burden in the skin of vertically infected dogs by RT-qPCR, despite these dogs not having received intradermal parasites via sand flies. There was a highly significant correlation between skin parasite burden at the feeding site and sand fly parasite uptake. This suggests dogs with high skin parasite burden contribute the most to the infected sand fly pool. Although skin parasite load and parasitemia correlated with one another, the average parasite number detected in skin was significantly higher compared to blood in matched subjects. Thus, dermal resident parasites were infectious to sand flies from dogs without detectable parasitemia. CONCLUSIONS/SIGNIFICANCE: Together, our data implicate skin parasite burden and earlier clinical status as stronger indicators of outward transmission potential than blood parasite burden. Our studies of a population of dogs without vector transmission highlights the need to consider canine vertical transmission in surveillance and prevention strategies.

Randomized, controlled, double-blinded field trial to assess Leishmania vaccine effectiveness as immunotherapy for canine leishmaniosis.

Better tools are necessary to eliminate visceral leishmaniasis (VL). Modeling studies for regional Leishmania elimination indicate that an effective vaccine is a critical tool. Dogs are the reservoir host of L. infantum in Brazil and the Mediterranean basin, and therefore are an important target for public health interventions as well as a relevant disease model for human VL. No vaccine has been efficacious as an immunotherapy to prevent progression of already diagnostically positive individuals to symptomatic leishmaniasis. We performed a double-blinded, block-randomized, placebo-controlled, vaccine immunotherapy trial testing the efficacy of a recombinant Leishmania A2 protein, saponin-adjuvanted, vaccine, LeishTec®, in owned hunting dogs infected with L. infantum. The primary outcome was reduction of clinical progression, with reduction of mortality as a secondary outcome. Vaccination as an immunotherapy reduced the risk of progression to clinically overt leishmaniasis by 25% in asymptomatic dogs (RR: 1.33 95% C.I. 1.009-1.786 p-value: 0.0450). Receiving vaccine vs. placebo reduced all-cause mortality in younger asymptomatic dogs by 70% (RR: 3.19 95% C.I.: 1.185-8.502 p-value = 0.0245). Vaccination of infected-healthy animals with an anti-Leishmania vaccine significantly reduced clinical progression and decreased all-cause mortality. Use of vaccination in infected-healthy dogs can be a tool for Leishmania control.

Adesão leucocitária e MDA sérico em cães naturalmente infectados por Leishmania infantum

O presente estudo avaliou o estresse oxidativo e a adesão de leucócitos (AL) em cães naturalmente infectados por Leishmania infantum. Foram utilizados cães saudáveis (CN = 10) e cães acometidos por leishmaniose visceral na forma sintomática (CS = 10), submetidos previamente a exames de imunofluorescência indireta (IFI), ensaio imunoenzimático (ELISA) e pesquisa do parasito em aspirados de medula óssea. Soro foi utilizado para avaliação de malondialdeído (MDA) no ensaio para espécies reativas ao ácido tiobarbitúrico (TBARS) e AL foi determinada pelo método da coluna de nylon em sangue em EDTA, heparina e citrato. Os dados de AL foram expressos em porcentagem e MDA em média ± desvio padrão, submetidos ao teste T de student não pareado (p 0,05). Amostras em heparina apresentaram níveis mais elevados de AL no grupo CS (55,62%, p 0,05) quando comparadas com EDTA e citrato (10,46% e 5,28%). Citrato e EDTA inibiram AL em cães doentes e saudáveis, enquanto a heparina preservou a AL. A proporção neutrofílica se apresentou reduzida nas amostras em heparina (85% para 67%, p 0,05) quando comparadas com citrato e EDTA, que por sua vez mantiveram-se estáveis (83% para 80%). Os níveis de MDA apresentaram-se mais elevados em CS (0,0117µM ± 0,002) quando comparado com CN (0,0057µM ± 0,001) (p 0,05). Estes dados dão suporte à conclusão de que na LVC ocorre elevação do estress