The pathology and pathogenesis of bluetongue.

Bluetongue (BT) is an insect-transmitted viral disease of wild and domestic ruminants and, occasionally, other species. Amongst domestic livestock, BT is most common in certain breeds of sheep whereas asymptomatic BT virus (BTV) infection of cattle is typical in enzootic regions. BT in cattle can be a feature of specific outbreaks, notably the current epizootic in Europe caused by BTV serotype 8. BTV replicates within mononuclear phagocytic and endothelial cells, lymphocytes and possibly other cell types in lymphoid tissues, the lungs, skin and other tissues. Infected ruminants may exhibit a prolonged but not persistent viraemia and BTV is associated with erythrocytes during the late stages of this prolonged viraemia. The pathogenesis of BT involves injury to small blood vessels in target tissues, but the relative contributions of direct virus-induced cytolysis and virus-induced vasoactive mediators in causing endothelial injury and dysfunction are presently unclear. The lesions of BT are characteristic and include: haemorrhage and ulcers in the oral cavity and upper gastrointestinal tract; necrosis of skeletal and cardiac muscle; coronitis; subintimal haemorrhage in the pulmonary artery; oedema of the lungs, ventral subcutis, and fascia of the muscles of the neck and abdominal wall; and pericardial, pleural and abdominal effusions. Transplacental transmission of BTV in ruminants, with subsequent fetal infection, is a property of specific virus strains, especially those propagated in embryonated eggs or cell culture. The outcome of BTV infection of fetal ruminants is age-dependent, with distinctive cavitating lesions of the central nervous system in animals that survive infection in early gestation. Immune competence to BTV arises by mid-gestation, and animals infected in late gestation can be born viraemic and without significant brain malformations.

[Bluetongue disease in Swiss sheep breeds: clinical signs after experimental infection with bluetongue virus serotype 8]. / Blauzungenkrankheit bei Schweizer Schafrassen: Klinische Symptome nach experimenteller Infektion mit dem BTV-Serotyp 8.

Clinical disease of bluetongue (BT) in sheep may differ depending on breed, age and immunity of infected sheep and may also vary between serotype and strain of BT virus (BTV). Since there are no data available on the susceptibility of Swiss sheep breeds for BT, we performed experimental infection of the 4 most common Swiss sheep breeds and the highly susceptible Poll Dorset sheep with the BTV serotype 8 (BTV-8) circulating in Northern Europe since 2006. Clinical signs were assessed regarding severity, localisation, progression and time point of their appearance. The results clearly show that the Swiss sheep breeds investigated were susceptible to BTV-8 infection. They developed moderate, BT-characteristic symptoms, which were similar to those observed in Poll Dorset sheep. Regardless of breed, the majority of infected animals showed fever, swelling of the head as well as erosions of the mouth and subcutaneous haemorrhages.