RB51 developer discusses challenges, potential vaccine advances in the future

Washington, D.C. – In February 1996, USDA’s Animal and Plant Health Inspection Service (APHIS) licensed the Brucella abortus strain RB51 vaccine for use in cattle to reduce the prevalence of brucellosis, eventually replacing the use of the Brucella abortus strain 19 vaccine in the United States.

“Strain 19 is not a bad vaccine. It gave very good protection, but it produces antibodies that screw up the virology and, long-term, makes it very hard to eradicate the disease,” noted Gerhardt Schurig.

Shurig, an immunology professor in the Department of Biomedical Sciences and Pathobiology at Virginia-Maryland College of Veterinary Medicine, presented some of the challenges of developing the RB51 vaccine on Nov. 11 in Washington, D.C. at the Revisiting Brucellosis in the Greater Yellowstone Area meeting, hosted by the National Academy of Sciences.

Different strains

“When I started the research, I wanted to find out what characteristics would make a better vaccine,” he explained.

There are two basic morphological forms of Brucella bacteria, a smooth form and a rough form. Strain 19 is composed of a smooth strain, which creates challenges related to antibody production and diagnostic testing for brucellosis.

“This point is important because we immediately began to think about using rough organisms, but how to select those rough organisms is where things became complicated,” he said.

The strain that is chosen must be attenuated, or weakened, so that it can be potentially administered to animals of any age.

“We don’t want to expose people to a disease if they are using a vaccine, and we certainly don’t want animals spreading the disease,” Schruig noted.

The Brucella strain also has to be stable and suitable for booster vaccines.

“It needs to be inexpensive and easy to administer as well,” he added.

Research

In 1979, Schurig and his team began developing tools to select for desired Brucella strains, and in 1982, they presented positive findings for a potential vaccine at a conference in Baton Rouge, La.

“From 1980 to 1996, there were basically 16 years between having the strain and applying it. It takes a long time to have something approved,” he commented.

Now, scientists are trying to improve the efficacy of the vaccine by modifying how antigen qualities are expressed by the RB51 Brucella strain.

“There are many antigens that have been described as having protective qualities against Brucella, but are they the correct ones to use in a particular species? I think that is a very important question,” Schruig said.

Ongoing exploration

In mice, scientists are seeing positive results, but cattle or bison may exhibit different responses to the same vaccine.

“We have to run those experiments, and that is where we get into trouble. It is now so expensive, and the regulatory things are so complicated, one kind of throws their arms up,” Schruig remarked.

Scientists are also interested in how RB51 impacts tuberculosis (TB). Along with modifying for increased protection against Brucella, Schruig and his team are hoping to create a strain that protects against TB as well.

“I think the concept is really valid,” he stated. “We believe we have the strain to protect against both, and now we have to test it.”

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be contacted at natasha@wylr.net.