Changes

When acute BVDV infection occurs during pregnancy, the dam may show any of the clinical manifestations that are seen in non-pregnant animals. BVDV is able to cross the placenta and infect the developing foetus and so there may be additional outcomes of infection that depend on the stage of gestation. If infection becomes established at the time of insemination, conception rates may be reduced, and early embryonic death is increased when the virus is introduced at a slightly later stage<ref name="foone">Carlsson, U et al (1989) '''Bovine virus diarrhoea virus: A cause of early pregnancy failure in the cow.''' ''Journal of Veterinary Medicine'', 36, 15-23.</ref><ref name="fotwo">Mc Gowan, M R et al (1993) '''Increased reproductive losses in cattle infected with bovine pestivirus aroung the time of insemination'''  ''Veterinary Record'', 133, 39-43.</ref>.  '''Foetal infection in the first trimester (50-100 days)''' may also result in '''death''', although expulsion of the foetus often does not occur until several months later. An additional effect of foetal infection before 120 days gestation is the birth of '''persistently infected (PI) calves'''.

When acute BVDV infection occurs during pregnancy, the dam may show any of the clinical manifestations that are seen in non-pregnant animals. BVDV is able to cross the placenta and infect the developing foetus and so there may be additional outcomes of infection that depend on the stage of gestation. If infection becomes established at the time of insemination, conception rates may be reduced, and early embryonic death is increased when the virus is introduced at a slightly later stage<ref name="foone">Carlsson, U et al (1989) '''Bovine virus diarrhoea virus: A cause of early pregnancy failure in the cow.''' ''Journal of Veterinary Medicine'', 36, 15-23.</ref><ref name="fotwo">Mc Gowan, M R et al (1993) '''Increased reproductive losses in cattle infected with bovine pestivirus aroung the time of insemination'''  ''Veterinary Record'', 133, 39-43.</ref>.  '''Foetal infection in the first trimester (50-100 days)''' may also result in '''death''', although expulsion of the foetus often does not occur until several months later. An additional effect of foetal infection before 120 days gestation is the birth of '''persistently infected (PI) calves'''.

'''Congenital defects''' can arise from transplacental infection '''between days 100 and 150'''. This is caused by an inappropriate inflammatory response mounted to BVDV by the immune system, which is undergoing the final phase of development at this stage<ref name="thfive"/>. Examples of common congenital abnormalities include defects of the thymus, ocular changes and cerebellar hypoplasia<ref name="thone"/>. Calves with cerebellar hypoplasia ataxic, reluctant to stand and may suffer tremors<ref name="thsix"/>, and ocular pathology often causes blindness and cataracts. Localisation of virus to the vascular endothelium gives vasculitis, leading to oedema, hypoxia and cellular degeneration. Weak, stunted calves may also be produced by BVDV infection in the second trimester.

'''Congenital defects''' can arise from transplacental infection '''between days 100 and 150'''. This is caused by an inappropriate inflammatory response mounted to BVDV by the immune system, which is undergoing the final phase of development at this stage<ref name="thfive"/>. Examples of common congenital abnormalities include defects of the thymus, ocular changes and cerebellar hypoplasia<ref name="thone"/>. Calves with cerebellar hypoplasia are ataxic, reluctant to stand and may suffer tremors<ref name="thsix"/>, and ocular pathology often causes blindness and cataracts. Localisation of virus to the vascular endothelium gives vasculitis, leading to oedema, hypoxia and cellular degeneration. Weak, stunted calves may also be produced by BVDV infection in the second trimester.

Infection in the '''third trimester trimester (over 180-200 days)''' elicits a response from the fully-developed immune system, giving rise to '''normal but seropositive calves'''.

Infection in the '''third trimester trimester (over 180-200 days)''' elicits a response from the fully-developed immune system, giving rise to '''normal but seropositive calves'''.