Research is under way at the ARS Animal Disease Research Unit in Pullman, Wash., to develop a vaccine that protects cattle against anaplasmosis, a tick-transmitted disease that threatens the health, wellbeing and production of cattle in many parts of the world.
At this time, there is no widely accepted vaccine for anaplasmosis. The disease, which is caused by the microbe Anaplasma marginale, can result in severe anemia, fever, weight loss and death in cattle.
ARS molecular biologist Susan Noh collaborated with scientists at Washington State University to identify significant proteins to include in a potential vaccine that is being tested on animals. They found that small groups of the outer surface proteins of A. marginale induce an immune response that reduces symptoms and also prevents A. marginale infection in some animals.
Among the vaccines being tested, some of those with the most potential have protected 80 to 90% of the animals from clinical disease and have prevented infection in up to 40% of the animals, Noh says.
"This is significant because infected animals may have no clinical evidence of infection, yet serve as sources of infection for others," Noh says. "No vaccine has ever prevented infection from A. marginale in cattle."
In other countries, an attenuated (weakened) strain (A. centrale) has been used as a vaccine that protects against clinical disease, but not infection, Noh says. Attenuated vaccines are prepared from live microorganisms or viruses that are cultured in the lab in such a way that they lose their virulence, but still confer disease immunity.
So far, scientists have only tested the vaccine against one strain of Anaplasma, whereas many strains coexist in the field. Their next step is to determine whether this particular group of proteins will protect cattle from various strains of Anaplasma.
This research is part of ARS National Program Number 103, Animal Health.