Pathogenesis of infection by bovine viral diarrhea virus in swine: reproductive, neonatal and neurological aspects

Abstract

The infection with Bovine Viral Diarrhea Virus (BVDV) in pigs may show clinical signs similar to those caused by the virus of classical swine fever. In ruminants, it is known that this virus can cause several problems, however, studies on the pathogenicity of BVDV in pigs are scarce. This project is divided into four studies that aim to elucidate important aspects of reproductive, neonatal and neurological pathogenesis caused by BVDV infection in pigs. The study 1 will evaluate the effect of BVDV-2 in different gestational periods in experimentally infected sows. BVDV-2 will be inoculated in ten pregnant gilts, which will be divided into five groups. The groups will be defined by inoculation at different times of the course of pregnancy. Blood samples will be collected every three days from the day of inoculation up to the day of delivery. Daily clinical evaluations will be performed in pregnant sows monitoring possible abortion. The study 2 aims to prove whether the BVDV-2 participates as an etiologic agent of Congenital Myoclonus in pigs. The action of the agent on the fetal central nervous system will be evaluated from the two experimental models: by oronasal inoculation of pregnant sows and by intrauterine fetal inoculation. For oronasal inoculation six gilts will be used in two experimental groups. In the group of four gilts, BVDV-2 will be inoculated at 45 days of gestation, and the group of two gilts will be the control. For the second experimental model, will be held fetal intrauterine inoculation by surgical procedure in two sows at 45 days of gestation. In both studies, 50% of piglets will be euthanized and necropsied on the day of birth to obtain samples of organs for histopathology, immunohistochemical and RT-PCR. The alive newborns will pass by daily clinical examination to assess the occurrence of neurological signs. The blood of the piglets will be collected every 3 days and observed until 35 days of age. Performed simultaneously, the study 3 aims to determine the condition persistently infected (PI) in piglets experimentally infected gilts with BVDV-2 in the second third of pregnancy (45 days). Hence, evaluations and samples collected from piglets during the 35 days will be used to identify the PI. If detected, the animals will be euthanized and necropsied to collect organ samples for testing by RT-PCR, histology and immunohistochemistry. The objective of the study 4 is to identify the importance of the boar in the transmission of BVDV in semen, evaluating the presence of BVDV, the effect on sperm cells and transmission capacity. Six boars will be used for experimental infection in a 90-day trial, with 45 days as the control phase and 45 days as inoculated phase. Samples of semen and blood will be collected every four days and analyzed by molecular, serological and spermatic ratings methods. For evidence of transmission of BVDV via semen, four gilts will be inseminated with semen originating from an infected boar which is excreting, and will be used in two gilts negative control. Monitoring will occur during 60 days of gestation, with blood samples collection every 4 days, and the tests used will be the RT-PCR and virusneutralization. (AU)