11 April 2012

4 minute read

Escherichia coli (E.coli) O157:H7 is commonly found in the intestines of animals and humans. According to the Centers for Disease Control (CDC) in Atlanta, Georgia, 73,000 people get sick and 61 people die from E. coli-related infections every year in the United States.

Cattle are considered to be one of the primary sources of E.coli. Numerous studies have shown that E. coli O157:H7 prevalence is widespread in dairy and beef animals and can be found in, on and around cattle in most parts of the world.

The E.coli is shed via cattle manure. The immediate source of most bacteria on carcases after slaughter is the contaminated hide. Through the Hazard Analysis Critical Control Points (HACCP) system, different controls have been put in place at slaughter to reduce contamination, including hide washing, careful hide and entrail removal and carcase steaming.

However, meat contamination by E. coli O157:H7 has not been eliminated and continues to be a persistent and costly problem for the industry.

How the vaccine works?

Mr Culbert explains that the vaccine works by stimulating cattle to mount an immune response against specific proteins of the E.coli O157 bacteria that are responsible for colonisation or adhesion in the intestine. If cattle have antibodies that block these adhesion proteins, then this specific bacteria is not able to become established and replicate in the intestine, which will reduce bacteria shed into the environment.

The vaccine consists of specific (Type 3 secretory) proteins that are required for colonisation. There are no live bacteria or whole cells in the vaccine – it is a bacterial extract (ie. secretory protein) vaccine, he explains.

While the vaccine doesn't kill the E.coli, it does stimulate an immune response to prevent that specific germ from causing an infection. The Econiche vaccine helps livestock to resist or overcome the E.coli O157. Asked why the government should pay, Mr Culbert says that this vaccine works specifically for E.coli O157.

"There are proteins in this vaccine that are similar to proteins in other variants of verotoxigenic E.coli, however we have not yet determined if this vaccine would cross protect against those other variants."

Controlled experiments have shown that cattle vaccinated shed significantly less E.coli than non-vaccinated cattle. Reduction in E.coli shed is typically around 65 per cent less, Mr Culbert says. However, another way to measure the efficacy of vaccine is to look at the reduction in colonisation. This, he says, shows a 98.2 per cent drop in colonisation.

Practical use of the vaccine

Mr Culbert says that Canada was the first country to licence the new vaccine in October 2008. "The Canadian regulators were clear about the type of data they needed. It was practical and possible to generate such data and, hence, the requirements were fulfilled."

Uptake of the vaccine in Canada is voluntary and at the moment stands at less than five per cent. Mr Culbert explains that vaccine users fall into two categories. Those whose farms have been associated with human illness due to E. coli O157, and those who participate in an integrated marketing programme whereby their cattle are linked to a particular “brand” of beef. In the latter scenario, it is the brand manager – not the feedlot operator - that makes the decision to further protect the brand by adding the value of a pre-harvest risk reduction step, he explains.

Cattle as young as three months can be vaccinated, although the vaccine has been used on younger calves. Mr Culbert says that cattle should be vaccinated twice in the first year, and once every year after.

Mr Culbert says that the vaccine sells at around C$3 per dose. Based on this, vaccinating cattle would cost producers C$6 per head in the first year, followed by an annual cost of C$3 per head thereafter.

There has been suggestions in Canada that the government should pay or donate towards a cattle vaccination programme. Mr Culbert says that the benefit of vaccinating cattle is purely a "public health" benefit.

Infection in cattle with E. coli O157 is asymptomatic. There are no clinical signs of illness in the cattle. There is no reduction in productivity or any animal health reason to vaccinate.

Reducing the amount of E. coli O157 shed by cattle and entering the environment reduces the risk of human exposure through contaminated drinking water, produce, beef, or via direct contact. The public health care costs associated with both primary and secondary illness due to E. coli O157 outweigh the cost of vaccinating the cattle, he explains.

There are no immediate benefits to the producers of vaccinating the cattle. The long-term benefit of vaccinating cattle against this human pathogen would be enhanced consumer confidence in beef safety, better acceptance of cattle rearing in proximity to rural neighbours, and the image of cattle farmers as responsible, caring members of society.

Talking about the approval process in the US, Mr Culbert says it is unknown whether the US Department of Agriculture will grant approval for the vaccine. In February 2008 the company was advised that the vaccine qualifies for a conditional licence in the US - however as yet this has not been granted.

Charlotte Johnston - Editor

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