NAVLE® QOD

Most of a litter of European wild boar at a zoological park have died. The surviving piglets are in lateral recumbency with a frothy nasal discharge.

Necropsy of the piglets reveals pulmonary edema and copious fluid in the trachea and bronchi along with grayish-white necrotic foci on the myocardium.

Which one of the following diseases is the most likely diagnosis?