Molecular aspects of some virulence factors of Haemophilus somnus.

Several virulence factors of Haemophilus somnus have been investigated, but to a varying extent. It is known that some isolates are more virulent than others. Factors associated with virulence include attachment to vaginal epithelial cells, turbinate cells or embryos; serum resistance; growth stimulation by normal flora; interference with phagocyte function; Fc receptors; and toxicity for several bovine cell types. Lipooligosaccharide and Fc receptors have been investigated at the molecular level and studies are in progress to relate their molecular structure to virulence.