Bovine viral diarrhoea virus: its effects on ovarian function in the cow

Bovine viral diarrhoea virus (BVDV) is a major cattle pathogen responsible for a spectrum of symptoms, including reproductive failure. In this paper w e investigate how BVDV interacts with the ovary. The viruses' tropism for t he pre-ovulatory oocyte was studied by indirect immunohistochemistry. Two m onoclonal antibodies, raised against the non-structural protein NS3 and the envelope glycoprotein E2 were used to probe cryo-sections cue from the ova ries of three persistently infected heifers. NS3 and E2 antigens were widel y distributed within the ovarian stroma and follicular cells. NS3 was also localised within the proportion of oocytes. Overall 18.7% of the oocyte pop ulation had detectable levels of NS3. What is more, the proportion of antig en positive oocytes remained constant (P > 0.05) throughout the different s tages of oocyte maturation. In a subsequent study seven cows were challenged with non-cytopathogenic BV DV (strain Pe515: 5 x 10(6) TCID50) to determine the oestradiol and progest erone responses to an acute infection. The sensitivity of the endogenous lu teolytic mechanism was also established by analysing plasma prostaglandin F 2 alpha metabolite (PGFM) levels following an exogenous oxytocin (50 TU) ch allenge. The inoculation was given 2 days before a synchronised oestrus and was timed to ensure that viraemia occurred during the initial stage of cor pora luteal development. Seven cows inoculated with non-infectious culture medium served as control animals and remained BVDV naive throughout the stu dy. The BVDV challenge was followed by leucopenia, viraemia and seroconvers ion. The virus also significantly (P < 0.01) reduced plasma oestradiol leve ls between day 6 and day ii post-inoculation (i.e. between day 4 and day 9 post-oestrus). However, the infection did not alter (P > 0.05) progesterone secretion throughout the oestrous cycle or the plasma concentration of PGF M. These data indicate that bovine follicular cells and oocytes are permissive to BVDV at all stages of follicular development. They also show that a tra nsient fall in oestradiol secretion may accompany an acute infection. In co nclusion, this work has identified two potential routes through which BVDV can reduce fertility in the cow, namely impairment of oocyte quality and di sruption of gonadal steroidogenesis. (C) 2000 Elsevier Science B.V. All rig hts reserved.