by Lucas Habib

A new vaccination technique used to reduce cattle stress and labour costs associated with traditional vaccination is being researched at the University of Guelph and at the Veterinary Infectious Disease Organization (VIDO) in Saskatoon. The work involves genetic engineering technology to develop a new generation of oral vaccines.

At the University of Guelph, Profs. Reggie Lo, Department of Microbiology, Patricia Shewen, Department of Pathobiology and Judith Strommer, Plant Agriculture are leading a team that’s developing an edible vaccine for shipping fever (pneumonic pasteurellosis) in cattle.

Vaccination by injection can be a really stressful experience for the cattle, and the producer, says Shewen. "That’s why it’s important to have a vaccine available that the cattle can be easily exposed to."

Traditional vaccines contain dead viruses or bacteria. But oral vaccines use a live form of the disease-causing agent (called a pathogen) that’s been modified to make it harmless. Modified-live vaccines induce much stronger and longer lasting immune responses, and help producers boost vaccine efficiency by administering them when the disease risk is greatest.

Shipping fever is the most common and problematic disease North American beef farmers have to contend with. The disease is caused by Mannheimia haemolytica, a bacterium which is normally found in the nasal pharynx of cattle. This bacterium is often inhaled, but is then cleared by the immune system.

However, when animals are under increased stress - such as when they’re shipped from one place to another - they often pick up viruses, which impair their ability to clear these bacteria, which then infect their lungs. Once in the lungs, the bacteria secrete a leukotoxin, a substance that kills white blood cells.

Current vaccines inject some leukotoxin into the cattle, which then produce antibodies to it. However, the vaccination process can be stressful for the animal and actually contribute to infection. For this reason, the research team has set out to explore possibilities of a genetically engineered edible vaccine.

Here’s how it works. The bacterial genes that produce the leukotoxin are inserted into a fibrous plant, such as clover or alfalfa, but with one important difference: the part of the gene that produces the toxic part of the leukotoxin is removed, meaning the plant produces harmless leukotoxins. Still, as the cattle chew the plants, the tonsils - which are organs in the immune system - are exposed to the leukotoxins, and antibodies are produced.

So far, laboratory animals have been introduced to the non-toxic leukotoxin, with the desired response. The next step is to start tests with cattle -- by painting the non-toxic leukotoxin on their tonsils -- and start feeding experiments in calves, in 2002.

"The unique thing about ruminants such as cattle, is that they regurgitate their food to chew again and again," says Shewen. "So, our vaccine exploits this physiological quirk to expose the tonsils to the toxin, to the animal’s ultimate advantage."

At VIDO, Dr. Philip Griebel has been working with bovine adenovirus, a virus that infects the respiratory and gastrointestinal tracts, but doesn’t cause disease. His research involves splicing certain genes from harmful viruses or bacteria into the adenoviruses, so that cattle infected with the adenovirus will develop immunity to the other pathogen. The vaccine is then fed to the cow in alginate, a common food additive. Research into the effectiveness of the method is ongoing, but if it performs well in the tests it will be another new weapon for the farmer’s arsenal in the struggle against disease.

Funding for the University of Guelph research is provided by the Natural Sciences and Engineering Research Council, the Ontario Cattlemen’s Association, and the Ontario Ministry of Agriculture, Food, and Rural Affairs.