Pathogenesis:
- Infection of alveolar macrophages is followed by an interstitial pneumonitis which may be complicated by secondary bacteria.
- Infection of (blood) monocytes which may persist in the presence of circulating antibody for up to 40 days. It is associated with immunosuppression.
- In sows viraemia may lead to transplacental infection then abortion or mummified foetuses or a return to service.
- Weak piglets with leucopoenia and thrombocytopoenia.
- Blue ear is rarely seen, but is a cyanotic appearance due to vascular lesions.