Humoral immunity in experimental thromboembolic meningoencephalitis in cattle caused by Haemophilus somnus.

Of 23 cattle inoculated IV with Haemophilus somnus, 16 (70%) died of thromboembolic meningoencephalitis. The inoculum was prepared from a minimally subcultured isolate of H somnus that was passaged through a calf by intracisternal inoculation immediately before use. Serum antibody titers, as measured by 7 serologic tests, were not correlated with the animal's susceptibility to infection. All cattle that died had a mean 4-fold increase in agglutination titer during the acute phase of the disease, 2 to 4 days after inoculation. Similarly, high acute-phase titers were demonstrated in 15 cattle with naturally occurring disease. Haemophilus somnus was isolated more frequently and in greater numbers from the CNS and urinary tract than from other organs of cattle that died.