Escherichia coli serotype O157:H7 causes illness in thousands of humans every year, and can be fatal. Results of a recent study published in the journal Vaccine now indicate that immunizing livestock against this bacterium could provide an effective method of minimizing its spread.

Although most people affected by E. coli O157:H7 experience only 'food poisoning' symptoms — such as diarrhoea — a proportion of cases result in potentially lethal kidney failure due to haemolytic-uremic syndrome, with ∼61 deaths per year resulting from O157:H7 infections in the United States alone. Most cases of human infection can be traced back to cattle through consumption of beef products or contaminated water, suggesting that vaccination of animals against the bacterium might decrease the number of people infected.

Brett Finlay and colleagues immunized eight calves with a vaccine containing the proteins EspA and Tir — part of a type III secretion system that is required for E. coli O157:H7 to colonize the host gut. Vaccinated animals showed a 45-fold increase in the production of specific antibodies against these proteins when an initial immunization was followed by a booster shot at 21 days. In addition, after experimental infection with the pathogen, the number of bacteria shed in faeces — a major route for the spread of infection between animals — was significantly lower in vaccinated calves than in animals that were given a placebo vaccine.

On the basis of these promising results, a second trial was carried out on yearling cattle. Finlay and co-workers found that the numbers of vaccinated cattle shedding O157:H7 fell to zero 6 days after infection, whereas ∼70% of animals that were administered a placebo were still shedding the bacterium at the same time-point. In addition, the number of bacteria present in faeces was markedly lower in the vaccinated animals.

Finally, the authors tested the effects of vaccination of a cattle population that were exposed to E. coli O157:H7 infection by natural means under typical agricultural conditions. A significant reduction in the shedding of the pathogen was seen among vaccinated cattle, with 8.8% of these animals releasing the bacterium in their faeces as compared with 21.3% of unvaccinated animals.

The study also suggested that just two rounds of immunization are likely to provide a sufficient level of protection to significantly reduce the spread of the bacterium, although further tests are required to confirm this. Together with the fact that the vaccine used is simple and cheap to produce, this highlights the immunization of cattle as a promising, economically viable method for curbing the number of animals infected with E. coli O157:H7 and lowering the risk of spread to the human population.