Non-suppurative myocarditis in piglets associated with porcine parvovirus infection

The involvement of porcine parvovirus (PPV) in the aetiology of non-suppurative myocarditis in sucking piglets was investigated by a polymerase chain reaction (PCR), designed to assess the presence of viral genome in formalin-fixed paraffin wax-embedded tissue of diseased animals. Myocardium and lung of stillborn piglets with a confirmed PPV infection were used to set up the PCR amplification method. Subsequently, 20 myocardia with inflammatory lesions were examined in parallel with 20 myocardia without lesions, from age-matched control piglets. Tissues were first tested for the presence and the integrity of porcine DNA by amplifying a sequence encoding the highly conserved nuclear protein histone H4. Tissue from 15 out of 20 animals with myocarditis contained amplifiable histone H4 DNA and in 12 of the 15 histone H4-positive samples, PPV DNA was detected. It proved possible to amplify histone H4 DNA in all 20 negative controls (without myocarditis), and PPV DNA was detected in three cases. In-situ hybridization with a digoxigenin-labelled probe homologous to PPV was performed in four PCR-positive cases of non-suppurative myocarditis. In two animals several positively stained nuclei were observed in the myocardium, within or close to the mild inflammatory cellular infiltrates. These results strongly suggest that PPV can cause non-suppurative myocarditis in sucking piglets.