Changes

== Clinical Signs ==

== Clinical Signs ==

Signs of IBR are variable but classically include '''coughing, serous nasal discharge, tachypnoea and dyspnoea'''. There may also be signs of increased '''lacrimation''' and a '''marked conjunctivitis'''. Coughing and sneezing are observed. The virus is excreted in the nasal secretions as early as 24 hours after infection. After an incubation period of 2 to 4 days, nasal secretions are more profuse and evolve from '''sero-mucous to mucopurulent discharge'''. The animal will usually be '''pyrexic''' and be weak, dull and depressed. It will usually have a reduced appetite and may show signs of weight loss. If in milk, the yield will be decreased. Young animals show ptyalism. In endemic dairy herds, it is not uncommon for animals to present with '''milk drop''' with or without pyrexia.

Signs of IBR vary with each particular strain but classically include '''coughing, serous nasal discharge, tachypnoea and dyspnoea'''. There may also be signs of increased '''lacrimation''' and a '''marked conjunctivitis'''. Coughing and sneezing are observed. The virus is excreted in the nasal secretions as early as 24 hours after infection. After an incubation period of 2 to 4 days, nasal secretions are more profuse and evolve from '''sero-mucous to mucopurulent discharge'''. The animal will usually be '''pyrexic''' and be weak, dull and depressed. It will usually have a reduced appetite and may show signs of weight loss. If in milk, the yield will be decreased. Young animals show ptyalism. In endemic dairy herds, it is not uncommon for animals to present with '''milk drop''' with or without pyrexia.

IBR may cause '''abortion''' if susceptible cows or heifers are infected during pregnancy.  Abortion is usually observed between '''4 and 8 months of gestation'''. Early embryonic death can also occur. Abortion is a consequence of '''respiratory infection of pregnant cows'''. Viraemia allows the virus to enter the uterine artery and cross the placenta. Abortion is due to a '''lytic infection''' of the fetus. All internal organs of the fetus, especially the '''liver and renal cortex''', show foci of necrosis. A generalized multifocal necrosis is diagnosed.<ref> Smith, K. C (1997) '''Herpesviral abortion in domestic animals'''. ''Vet Journal'', 153(3):253-268</ref> Infection of cows during the last trimester of gestation can lead to '''neonatal death''', and death of weak calves can occur during the first 2 weeks of life.<ref> Thiry, E., Detilleux, P., Vriese, A., Pirak, M., Pastoret, P-P (1984) '''Infectious bovine rhinotracheitis in the neonatal period: a review and a case report.''' ''Annales de Médecine Vétérinaire'', 128(1):33-40; 25</ref>

IBR may cause '''abortion''' if susceptible cows or heifers are infected during pregnancy.  Abortion is usually observed between '''4 and 8 months of gestation'''. Early embryonic death can also occur. Abortion is a consequence of '''respiratory infection of pregnant cows'''. Viraemia allows the virus to enter the uterine artery and cross the placenta. Abortion is due to a '''lytic infection''' of the fetus. All internal organs of the fetus, especially the '''liver and renal cortex''', show foci of necrosis. A generalized multifocal necrosis is diagnosed.<ref> Smith, K. C (1997) '''Herpesviral abortion in domestic animals'''. ''Vet Journal'', 153(3):253-268</ref> Infection of cows during the last trimester of gestation can lead to '''neonatal death''', and death of weak calves can occur during the first 2 weeks of life.<ref> Thiry, E., Detilleux, P., Vriese, A., Pirak, M., Pastoret, P-P (1984) '''Infectious bovine rhinotracheitis in the neonatal period: a review and a case report.''' ''Annales de Médecine Vétérinaire'', 128(1):33-40; 25</ref>