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====Acute Infections: Pregnant Animals====

====Acute Infections: Pregnant Animals====

Immunocompetent, pregnant cattle show the same responses to BVDV infection as non-pregnant animals. However, BVDV has a high potential to cross the placenta and infect the developing foetus, meaning additional outcomes of infection may occur in the calf. The main factor influencing the virus’s effects on the foetus is the gestational age at the time of transplacental infection.

Immunocompetent, pregnant cattle show the same responses to BVDV infection as non-pregnant animals. However, BVDV has a high potential to cross the placenta and infect the developing foetus, meaning additional outcomes of infection may occur in the calf. The main factor influencing the virus’s effects on the foetus is the gestational age at the time of transplacental infection.

Infection at the time of insemination may result in reduced conception rates, and that shortly after increases loss of embryos (Carlsson et. al, 1989; McGowan et. al, 1993). Foetal infection in the first trimester (50-100 days) can cause death, although expulsion of the foetus may not occur until several months later.

Infection at the time of insemination may result in reduced conception rates, and that shortly after increases loss of embryos (Carlsson et. al, 1989; McGowan et. al, 1993). Foetal infection in the first trimester (50-100 days) can cause death, although expulsion of the foetus may not occur until several months later.

Transplacental infection between days 100 and 150 may result in congenital defects. At this stage the immune system is in the final phase of development, and mounts an inappropriate inflammatory response to BVDV to cause these effects (Duffell and Harkness, 1985). Growth defects in organs such as the thymus, and central nervous system pathologies such as cerebellar hypoplasia, often arise (Brownlie, 1985). Calves with cerebellar hypoplasia are ataxic, reluctant to stand and may suffer tremors (Baker, 1995). Infection at this point may also cause visual problems, including blindness and cataracts. Virus may localise to the vascular endothelium, causing vasculitis and associated inflammation, oedema, hypoxia and cellular degeneration (Brownlie, 2000). Weak, stunted calves may also be produced.

Transplacental infection between days 100 and 150 may result in congenital defects. At this stage the immune system is in the final phase of development, and mounts an inappropriate inflammatory response to BVDV to cause these effects (Duffell and Harkness, 1985). Growth defects in organs such as the thymus, and central nervous system pathologies such as cerebellar hypoplasia, often arise (Brownlie, 1985). Calves with cerebellar hypoplasia are ataxic, reluctant to stand and may suffer tremors (Baker, 1995). Infection at this point may also cause visual problems, including blindness and cataracts. Virus may localise to the vascular endothelium, causing vasculitis and associated inflammation, oedema, hypoxia and cellular degeneration (Brownlie, 2000). Weak, stunted calves may also be produced.