Abstract:

Toxocara canis is the helminth agent of toxocariasis, whose definitive hosts are canines, but it affects humans and other mammals as paratenic hosts, causing multiple clinical pictures, and occurs worldwide, predominating in tropical and developing countries. There is a need for the development of vaccines to prevent this infection. Thus, in this study it was possible to identify by in silico analyses, several potential T. canis proteins for the development of a canine vaccine. After expression in procaryote systems of three molecules (rTcCad, rTcVcan, rTcCyst), they were purified and tested in a murine model of toxocariasis using C57BL/6 female mice; the mice were immunized with each or with combinations of the recombinant antigens, prior to challenge with 500 T. canis embryonated eggs. It was evaluated the production of anti-T. canis IgA, IgE, IgG (IgG1-IgG2a), as well as the in-vitro production of cytokines such as IL-5, INF-g and IL-10 by spleen cells. The groups vaccinated with the rTcCad and rTcVcan molecules generated a mixed Th1/Th2 immune response. In relation to the migration of larvae in different tissues, vaccination with rTcCad and rTcVcan with CFA reduced larval loads in mice exposed to T. canis by 54.3% and 53.9% (p <0.0001), respectively, compared to non-immunized controls. The best proteins were then evaluated using different adjuvants. When QuilA® was added as adjuvant to rTVcan, protection against larval migration increased markedly to 73.2% (p<0.0001). In canines, this vaccine formulation (rTcVcan+QuilA®) generated a significant reduction (70-90%) in the parasite load according to the egg counting in feces (p<0.0001), a significant reduction (50-60%) in eggs extracted from the uterus of pharmacologically expelled T. canis females (p<0.001) and a mixed Th1/Th2 response of cytokines produced by PBMC. Concluding, the mixed Th1/Th2 response of cytokines with an adequate level of antibodies (IgG) promoted significant protection of canines against toxocariasis under controlled laboratory conditions. From our knowledge, this is the first clinical trial in the World of a vaccine using T. canis recombinant proteins. It has shown promising results in the control of canine toxocariasis, which may impact animal health and the public health by controlling canine infection and indirectly of human toxocariasis. Biography:

NMAN – Graduated at Medicine from Universidade Federal da Bahia (UFBA) Medical School (1977), master’s at Medical Parasitology from University of London (1981) and PhD. In Molecular and Celular Biology (Fundação Oswaldo Cruz, Brazil, 1998). Works as Associate Professor of UFBA/Brazil. Has experience in immunoparasitology, acting on the following subjects: Association of helminth with asthma and allergy; development of allergens and helminths molecules for immunodiagnosis, immunotherapy and immunoprophilaxis purposes.

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