Valuation of Two Types of Delivery of DNA Vaccines Against Canine Leishmaniasis
*Juan José Zárate Ramos, Ignacio Arbea Sarasa, Pablo Gómez Ochoa, Juan A. Castillo Hernández, Vicente Larraga de Vera, María Jesus Ramiro Ibañez
Canine leishmaniasis is a zoonotic disease spread worldwide. The protozoa responsible of the visceral form of the disease, Leishmania infantum, has the main reservoir in the dog, although other mammals like foxes, wolves or rats have been demonstrated, is the causing agent. In order to fight against leishmaniasis vaccine prophylaxis has been focused as the best way to prevent human disease. The main objective of this work is to evaluate the ability to protect dogs from infection by Leishmania infantum. Also a comparison between two types of delivery of recombinant vaccines were performed. One of them constituted by " DNA-LACK plasmid" and the other using a "prime-boost" regime with the same plasmid plus a recombinant vaccinia virus "rVV-LACK."
Twenty Beagle dogs were included in the assay, five of them were used as a negative control (without infection). The other 15 dogs were infected with 100 millions of Leishmania promastigotes intravenously. Five of teen were previously vaccinated with two doses of a DNA-LACK plasmid and the other five with the plasmid plus a recombinant vaccinia virus rVV-LACK. The resting five dogs were infected and not vaccinated. Scheduled controls were performed evaluating: a) weight b) symptom presentation c) DAT-serologic method- d) parasitic isolation d) PCR cytokine determination. The samples used for the study were, blood from jugular vein, lymph node and bone marrow aspiration. At the end (497th day) all dogs were euthanized, and samples of all tissues( spleen, liver, lymph nodes and skin) were taken. Tissue impressions- parasite load- and pathological study were carried out.
All the positive controls became infected, showing different kind of symptoms (alopecia, waste, lymph node enlargement, dry exfoliative dermatitis, muscle atrophy...). At 9th month first positive serum was recorded in this group. The parasite was seen in all these animals. In plasmid vaccinated group and in two dogs from plasmid/vaccinia group, the parasite was isolated in all the animals, that show many symptoms. Nevertheless, in plasmid/vaccinia group 3 out five showed protective immune response. None parasite was detected in tissue impression neither in the histological examination. Moreover, they did not exhibit any symptom of the disease. These three dogs (60%) were serologically negative during all assays.
Experimental infection can be obtained in dogs with L. infantum promastigotes using a dose of 108 promastigotes/animal.
Under the experimental conditions of this work, the vaccine DNA-LACK plasmid, was not able to protect the animals, on the other hand, histopathologic lesion and parasitic charge were lower in this group than in the control positive group.
Under the conditions of this work, the recombinant vaccinia virus rVV-LACK protect of the infection 3 out 5 animals and four of five of the clinical leishmaniasis signs. In the positive animals of this group the parasite load and histopathological lesions were milder than those of the ones observed in the control positive group.