UA researchers are finding a new way to reduce food-borne illness in humans
Oct 28, 2008 10:08 AM,
By Susan McGinley
University of Arizona College of Agriculture and Life Sciences
Most people are familiar with Salmonella and its potential to make people ill. But fewer know about Campylobacter jejuni – even though it makes more people sick. Raw chicken is one of the most common carriers of the bacteria, often encountered when cooked meat is placed on unwashed cutting boards previously used for trimming raw chicken, or when chicken is not cooked to 165 degrees Fahrenheit.
"Campylobacter is now the No. 1 food-borne pathogen in the United States and the world, surpassing Salmonella," said Lynn Joens, a professor at the University of Arizona (UA) Department of Veterinary Science and Microbiology. "In the United States alone, 2.4 million cases are reported annually, with costs exceeding $1 billion."
A new poultry vaccine in development at UA offers a unique approach in controlling Campylobacter jejuni infection in chickens before it reaches the dinner table. In research trials the vaccine has significantly reduced the pathogen's ability to colonize young chickens' intestines, where the infection begins. The goal is to halt the contamination before it spreads and survives on raw chicken sold in stores.
"Yet chickens don't actually cause the disease (nor does it make them ill). It's the organism they carry that makes people sick," Joens said. "Right now you can go to any grocery store, get a raw chicken, test it in a laboratory and find Campylobacter jejuni. Twenty percent to 80 percent of all broiler houses become contaminated with Campylobacter."
The most common symptoms of human Campylobacter poisoning, which mimic those of Salmonella and other gastrointestinal pathogens, include fever, cramps, watery diarrhea and sometimes dysentery. More severe infections can lead to peritonitis, autoimmune disease or death.
Funded by the U.S. Department of Agriculture, Joens and UA graduate students started analyzing Campylobacter's infection process about four years ago, looking for a way to interrupt it. The laboratory team, which included James Theoret, graduate research associate, and Bibiana Law, assistant research professor, eventually discovered that the pathogen first attached itself to the surface of the chick's intestines and then began to multiply. Attacking the "sticking" mechanism seemed to be the key.
When UA researchers sequenced the intestinal surface protein they identified the gene responsible for producing Campylobacter’s adherence protein. Then they built a trial vaccine around it using Salmonella bacteria as a vector, with the assistance of Roy Curtiss, professor and director of the Center for Infectious Diseases and Vaccinology at Arizona State University.
Curtiss’ group inserted the adherence gene into Salmonella bacteria, which is nonpathogenic for poultry. The resulting live vaccine – containing Salmonella programmed to make the Campylobacter adhering protein – was fed to young chickens to protect them.
“Once the Salmonella in the vaccine produced the Campylobacter protein, the chicks made antibodies against it in their intestines,” Joens says. "In our first study of 15 birds we got a very significant reduction – 98 percent – in Campylobacter infection, compared with a control group. We're now repeating the trial on a larger scale."
The vaccination process is simple, easy to produce and protective to the chick, according to Joens. The Salmonella lives four to five days, enough time to stimulate antibody production, and dies. Chickens need to be vaccinated early because they become infected at just two to three weeks of age.
Joens' preliminary figures show that 270 million Campylobacter organisms were present in non-vaccinated birds, compared with 67,000 organisms in the vaccinated birds.
"You need at least 500 organisms to produce disease in humans," he explained. "The chlorine in the packinghouse chillers usually reduces numbers of bacteria by 1,000 to 100,000 organisms, so the chickens should be free of Campylobacter after processing."
The UA group was the first to discover the adherence protein, which is only produced when Campylobacter jejuni colonizes certain surfaces, like chicken intestine and skin. They have a patent pending in both the United States and the European Union for the gene that produces it.
"If everything goes right we could have a commercial vaccine in three to five years," Joens said.
The vaccine's effect could be significant: About 8.9 billion broilers go to market annually in the U.S., with a value of $21.5 billion. Europe has similar broiler production figures. Americans consumed 86 pounds of chicken per person in 2006, the most recent numbers available.
"The vaccine would be a great intervention method for Campylobacter when the USDA and FDA (Food and Drug Administration) mandate reduced numbers of food-borne pathogens in chicken – probably in two to three years," Joens said. "Once it becomes available, the vaccine should cost about a penny per chick. More importantly, it should greatly reduce the number of cases of human Campylobacter gastroenteritis."
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