In-situ hybridization for the detection of Haemophilus parasuis in naturally infected pigs

Detection of Haemophilus parasuis in naturally infected pigs was studied by in-situ hybridization with a non-radioactive digoxigenin-labelled DNA probe. Twenty pigs were selected on the basis of bacterial isolation and histopathological lesions. An 821 base pair DNA probe from the 16S small subunit ribosomal RNA (rRNA) was generated by the polymerase chain reaction. Hybridization signals were detected in formalin-fixed, paraffin-wax-embedded tissues (lung, heart, spleen and liver). Identification of the cell types containing H. parasuis was occasionally difficult, but examination of adjacent sections stained with haematoxylin and eosin confirmed that positive cells resembled either macrophages (large oval nuclei and abundant cytoplasm) or neutrophils (bilobed nuclei). In-situ hybridization would appear to be a valuable tool for the diagnosis of H. parasuis infection.