Serum cross-reaction among virulence-associated trimeric autotransporters (VtaA) of Haemophilus parasuis.

Glässer's disease is a fibrinous polyserositis and polyarthritis of swine caused by the bacterium Haemophilus parasuis. Control by vaccination has been limited for years due to lack of cross-protection among strains. However, 6 trimeric autotransporters (VtaA) of the Nagasaki strain were shown to be antigenic and gave partial protection to a lethal challenge. The antigenic relationship among the VtaAs was examined by immunizing mice with individual VtaA showing that they cross-reacted by ELISA mainly with VtaA from the same group. When sera from protected and non-protected vaccinated piglets were examined no differences in VtaA cross-reactivity profiles were found. In addition, sera from commercial pigs immunized with a single VtaA (VtaA9) showed a wider range of VtaA cross-reaction, probably due to the previous colonization by H. parasuis. These results can help the development of new vaccine formulations against H. parasuis by allowing a rational VtaA selection.