By Doug Rich

There is some good news about bovine spongiform encephalopathy, according to Don Knowles with the U.S. Department of Agriculture ARS Animal Disease Research Unit. Knowles was part of a panel discussion on beef safety during the 2005 Cattle Industry Convention and Trade Show.

Knowles said there are three things we need to know about a contagious disease: how it is transmitted, how it is transmitted, and how it is transmitted. The good news is that BSE does not transmit from cow to cow. "This is not a communicable disease," Knowles said. "The main source of transmission is through feed stuffs. There has been some confusion about the means of transmission because of two other similar prion diseases, chronic wasting disease (CWD) found in elk, mule and white tailed deer and scrapie in sheep. CWD and scrapie can be transmitted from animal to animal within a herd or flock. "BSE does not go cow to cow in the absence of recycled protein. This means that BSE can be easily controlled."

He attributes the remaining low level incidence of BSE to contaminated feed that was distributed prior to understanding the path of transmission or to the possibility of spontaneous BSE. "There is a sporadic form of prion disease in humans called Creutzfeldt-Jakob disease (CJD)," said Knowles.

"With the ban on feeding recycled protein back to cattle and the lack of other routes of BSE transmission, the levels of BSE globally should continue to decline," Knowles said. "With this decline in BSE, the risk of BSE transmission to humans will decline also."

There has been some concern about new strains of BSE. When atypical BSE is discovered researchers look to see if it has developed a new path of transmission, if it is more efficient, or if it hampers their ability to diagnose the disease. So far none of the new strains have done any of those things. "What we need to continue to do is be vigilant, but to look for changes that alter our ability to control the disease," Knowles said.

To monitor the BSE in the U.S. beef herd and to gain an idea of the risk, an enhanced BSE surveillance plan was implemented on June 1, 2004. Terry McElwain, professor and executive director of the Washington Animal Disease Diagnostic Laboratory at Washington State University, provided a state laboratory perspective of the surveillance program.

"The goal of the surveillance plan is to test as many high risk animals as necessary to establish with 99 percent confidence whether BSE is present in the U.S. and if so at what level, and to meet OIE guidelines for ensuring open trade," said McElwain. The target population for these tests consists of animals that have some sort of disorder that would be compatible with clinical signs of BSE. This high risk group includes animals with central nervous system disorders, all non-ambulatory animals, and dead cattle above the age of 30 months. "The ability to pick up signs of BSE is enhanced 10 to 20 percent by using a target population," said McElwain.

There are approximately 466,500 cattle in this target population in the U.S. It was decided that 268,500 animals in this group should be tested to provide an accurate sample. "A target number for testing in each state was established to meet this national goal," said McElwain. Nearly 1,700 animals are tested every day at seven accredited state diagnostic laboratories around the country. Five other laboratories are now approved and waiting to be licensed through the USDA. As of Jan. 22, 203,122 tests had been completed and no cases of BSE had been identified. At this rate the surveillance program will be completed by June 1, 2005. "There are five infected animals or less in this country with BSE if we get negative results from this sample."

When to make a public announcement of a reactor, a sample in which the colorimetic value is above the cutoff for a negative test, has created some controversy since the surveillance program began in June 2004. At the present time if a single well test is identified as a reactor it is not reported to the public. The sample is rerun that same day using a two well test. "Samples are sent immediately to the National Veterinary Services Laboratory in Ames, Iowa," said McElwain. "If both of the two follow-up test wells are negative, the test is determined to be a true negative and no further action is taken. If either of the two wells in the follow-up test is a reactor the result is classified as inconclusive." At this point, according to USDA policy, public notification is made at this time. All tests have been negative so far.

E. coli progress

Although BSE gets all of the headlines, E. coli 0517 is still a threat to beef safety in this country. Much of the research on methods for controlling E. coli have been focussed at the packer level but new research has switched to the pre-harvest or feedlot stage of production. "Research shows that what happens pre-harvest impacts the likelihood of a carcass becoming contaminated," said Guy Loneragan, West Texas A&M University.

"The incidence of E. coli has dropped dramatically from a high of 2.7 reported cases per 100,000 people in 1996 to 1.1 cases per 100,000 people in 2003," said Loneragan. "Much of this improvement is a result of development of interventions targeted at packing plants. However, recent studies have highlighted the need for effective pre-harvest interventions to combat this organism." Direct fed microbials or probiotics have reduced the percentage of positive cattle going to harvest. These products contain strains of beneficial bacterium Lactobacillus. Probiotic products reduced the number of cattle that are positive and even reduced the amount of bacteria in cattle that are still positive. "These products have decreased the pathogen load quite dramatically."

"In addition to direct-fed microbials, prototype vaccines appear to be very efficacious too," said Guy Loneragan. "One such vaccine reduced the percentage of positive cattle by an average of 58 percent over two studies compared with controls." The combination of pre-harvest and harvest interventions should continue to improve the safety of beef products in this country.

Perception and reality often provide different views of the same picture. Beef safety research injects a dose of reality into the perception of beef products in this country and with our export customers.

Date: 3/1/05

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