Bovine Herpes Virus 1 (BoHV-1) and its various subtypes are double-stranded DNA viruses and belongs to the Herpesviridae family, which is usually introduced into BHV-1-free farms by purchasing animals that are clinically healthy but are latent carriers of the virus or are in the incubation phase. The spread of the disease is promoted by intensive animal movements, e.g. by livestock traders and livestock markets, and is mainly spread in the herd through direct contact with animals, e.g. via tear and nose secretion containing the pathogen (droplet infection), via the mucous membranes of the genital tract, but also via faeces. Indirect transmission through persons and contaminated clothing, through insufficiently cleaned, contaminated transport vehicles, equipment (stable utensils) and instruments (e.g. hypodermic needles) is also possible. Infected animals remain carriers of the virus for life. The virus can be shed again in phases after a stressful situation (e.g. change of feed, birth, transport, stress). Nasal virus shedding lasts up to 2 weeks. Male animals play an important role in the spread of IBR/IPV/IBP (sending of infected semen). The affected cattle show serologically detectable antibodies 7-14 days after infection. Maternal antibodies are transmitted to the calves via colostrum, which provides them with biological protection against clinical disease. In most cases they are detectable up to 9 months, in a few cases even longer. Small ruminants can become infected, shed the virus, but do not show any symptoms of the disease. Wild ruminants form a virus reservoir in BHV-1 areas.
From the clinical picture, infection with BHV-1 appears in two forms, the symptoms of the disease vary depending on the age of the infected animals:
IBR = respiratory form: Fatigue, anorexia, fever (up to 42 °C), nasal discharge, hyperemia of the nasal and floppy mucosa ("red nose symptom"), conjunctivitis, cough, dyspnoea, miscarriage, fattening animals show reduced fattening performance. Lactating animals show a strong decrease in milk yield already at the beginning of the disease. In calves, IBR occurs mainly as a febrile general disease with a predominance of respiratory symptoms and often diarrhoea. The mortality rate is significantly higher than in adult animals.
IPV / IBP = genital form (usually restricted to the vaginal and preputial mucosa): fatigue, inability to eat, fever (up to 42 °C), swollen and oedematous labia, hyperemic mucosa (atrium, vagina, penis), vesicles on the mucosa, abortion, orchitis, endometritis.