Field trial of efficacy of the Leish-tec® vaccine against canine leishmaniasis caused by Leishmania infantum in an endemic area with high transmission rates

Because domestic dogs are reservoir hosts for visceral leishmaniasis (VL) in Brazil, one of the approaches used to reduce human disease incidence is to cull infected dogs. However, the results of controlled intervention trials based on serological screening of dogs and killing of seropositive animal...

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Bibliographic Details
Published in:PloS one 2017-09, Vol.12 (9), p.e0185438-e0185438
Main Authors: Grimaldi, Jr, Gabriel, Teva, Antonio, Dos-Santos, Claudiney B, Santos, Fernanda Nunes, Pinto, Israel de-Souza, Fux, Blima, Leite, Gustavo Rocha, Falqueto, Aloísio
Format: Article
Language:English
Subjects:
Animals
Antibodies
Antibodies, Protozoan - biosynthesis
Biology and Life Sciences
Brazil - epidemiology
Clinical trials
Culling
Disease control
Disease Progression
Disease transmission
Dog Diseases - epidemiology
Dog Diseases - prevention & control
Dog Diseases - transmission
Dogs
Immunization
Immunogenicity
Immunoglobulin G
Immunoprophylaxis
Incidence
Infections
Infectious diseases
Intervention
Leishmania
Leishmania infantum
Leishmania infantum - immunology
Leishmania infantum - isolation & purification
Leishmaniasis Vaccines - therapeutic use
Leishmaniasis, Visceral - epidemiology
Leishmaniasis, Visceral - prevention & control
Leishmaniasis, Visceral - transmission
Leishmaniasis, Visceral - veterinary
Lutzomyia longipalpis
Medicine and Health Sciences
Parasites
Parasitic diseases
Prevalence
Prospective Studies
Research and Analysis Methods
Seroconversion
Vaccines
Vector-borne diseases
Visceral leishmaniasis
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Summary:Because domestic dogs are reservoir hosts for visceral leishmaniasis (VL) in Brazil, one of the approaches used to reduce human disease incidence is to cull infected dogs. However, the results of controlled intervention trials based on serological screening of dogs and killing of seropositive animals are equivocal. A prophylactic vaccine to protect dogs from being infectious to the sand fly vector could be an effective strategy to provide sustained control. Here, we investigated whether a currently licensed commercial subunit rA2 protein-saponin vaccine (Leish-tec®) had an additional effect to dog culling on reducing the canine infectious populations. This prospective study was conducted in an L. infantum highly endemic area of southeast Brazil. At the onset of the intervention, all of the eligible dogs received through subcutaneous route a three-dose vaccine course at 21-day intervals and a booster on month 12. For the purpose of comparison, newly recruited healthy dogs were included as the exposed control group. To ascertain vaccine-induced protection, dogs were screened on clinical and serological criteria every 6 months for a 2-year follow-up period. Antibody-based tests and histopathological examination of post-mortem tissue specimens from euthanized animals were used as a marker of infection. The standardized vaccine regime, apart from being safe, was immunogenic as immunized animals responded with a pronounced production of anti-A2-specific IgG antibodies. It should be noted the mean seroconversion time for infection obtained among immunized exposed dogs (~ 18 months), which was twice as high as that for unvaccinated ones (~ 9 months). After two transmission cycles completed, the cumulative incidence of infection did differ significantly (P = 0.016) between the vaccinated (27%) and unvaccinated (42%) dogs. However, the expected efficacy for the vaccine in inducing clinical protection was not evident since 43% of vaccine recipients developed disease over time. Our estimates also indicated that immunoprophylaxis by Leish-tec® vaccine in addition to dog culling might not have an impact on bringing down the incidence of canine infection with L. infantum in areas of high transmission rates. Leish-tec® as a prophylactic vaccine showed promise but needs to be further optimized to be effective in dogs under field conditions, and thereby positively impacts human incidence.
ISSN:1932-6203
1932-6203
DOI:10.1371/journal.pone.0185438