Vaccinia bovina em vacas secas e lactantes experimentalmente inoculadas com o Vaccina virus

Abstract

This dissertation was divided into three experiments whose aims were to reproduce the bovine vaccínia (BV) in crossbred dairy and dry cows through the experimental inoculation with Vaccinia virus Guarani P2 (VACV-GP2). Experiment 1 studied the clinical and pathological evolution of the lesions and the localization of the virus by immuno-histochemistry in different stages of the disease. In this experiment, the teats of six crossbred dry cows, divided into three groups, were scarified with a hypodermic needle in the central area of each teat. Two groups were euthanized and necropsied in different stages of the disease, while in a third group, a biopsy was performed in the inoculated area of the teats In the experiment 2, three crossbred cows were inoculated in order to analyze different scarification methods and the pathogenicity of two different inocula with VACV-GP2. One cow was euthanized on the 17th day post-inoculation (d.p.i), period in which the lesions were healed. The aims of experiment 3 were to carry out clinical, hematological and biochemical analysis associated to the infection and to observe the effects of immunodepression and re-infection with VACV-GP2 in dairy cows previously infected by VACV. The experiment was divided into two parts. In part 1, eight crossbred dairy cows were inoculated with VACV-GP2 and in part 2, the cows from experiment 1 and 3 (part 1) were immunodepressed or reinfected. All animals in experiments 1, 2 and 3 were observed for 32 days and clinical examination was done every other day. Moreover, blood, faeces, oral swab and milk samples were collected daily and the technics employed were IPMA, seroneutralization and PCR. Several tissues were collected in necropsies and analysed through HE and IHC. Biochemical and hematological analysis and somatic cell count (SCC) in milk were done only in experiment 3. In all experiments it was observed that the incubation period was short and the evolution of the lesions was similar among the animals experimentally infected. Moreover, these lesions were also similar to the ones in cows naturally infected. Through clinical monitoring, it was observed that experimental infeccion of VACV in bovines causes local lymphadenopathy. Neither hyperthermy nor clinical alterations were detected. In the inoculated animals from experiments 1 and 2, histological alterations were observed in the teats, mammary glands and mammary lymph nodes in the three different phases of the disease, i.e., ulcerative, crust and healing. Through IHC, the VACV was detected in teats, as well as in mammary glands and mammary lymph nodes on the 3th, 9th and 17th d.p.i. During the experiment the mastitis was exacerbated by BV, which was shown by the increase of SCC in milk, and the dairy cows had intense decrease in milk production. lymphopenia and neutrophilia,which may be associated with viral infection and mastitis, respectively, were observed in the hematological analysis. In the experimental conditions which the cows were tested, it was possible to conclude that reinfection by VACV can occur in previously infected animals. There is a suspicion that the VACV can persist and multiply in immunodepressed bovines, once that there was an increase in antibodies titers in these animals. Lastly, some results suggest that the VACV can spread systematically in cattles, since the viral DNA was detected in the oral mucosa lesions.