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A cure for livestock respiratory disease has long eluded researchers. This ailment costs U.S. and Canadian cattle producers more than $1 billion annually. But now a new live vaccine developed by Agricultural Research Service (ARS) researchers promises to substantially reduce these losses. Shipping fever affects calves about one week after they are transported from the cow/calf operations to the feedlots. The culprits are three different bacteria-Pasteurella haemolytica, P. multocida, and Haemonphilus somnus. The stresses of handling and shipping cause a weakened immune system which allows the bacteria to cause pneumonia. Animals that look healthy when purchased may arrive with symptoms such as decreased appetite, fever and nasal discharge. 
ARS veterinarian Robert E. Briggs and microbiologist Fred M. Tatum created a live vaccine by deleting a large piece of gene called aroA from each of the three bacteria. Without this gene, the bacteria do not cause infection.These are the first genetically engineered vaccine strains for shipping fever that have been made without using foreign DNA or a marker for antibiotic resistance, says Tatum. Most shipping fever vaccines are made from bacterins--suspensions of killed bacteria-or from specific bacterial proteins. A live vaccine is more effective because it gives disease resistance much like convalescent immunity to the animal, says Briggs. Similar to what happens when someone recovers from mumps or measles, this type of immunity is typically stronger and longer lasting than that conferred by killed vaccines. Several patents on the vaccine technology have been issued jointly to ARS and the Biotechnology Research and Development Corporation (BRDC). BRDC is a public/private organization formed to speed commercialization of government-funded research discoveries. Schering Plough, a member company, has licensed the technology to make multivalent injectable vaccines and is in the process of getting approval to market the new product. Briggs and Tatum are also working on an oral vaccine that can be given to animal as part of their feed ration. Recently, 100head of cattle were shipped from Tennessee to Texas. Come of the calves received the oral vaccine four days before shipping and others didn't. All of the calves fed the oral vaccine were protected. If proven effective, producers might find feeding the vaccine is easier and less time consuming than intramuscular injections. |
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