Vaccinating Cows Could Sharply Reduce E. Coli Infections

Widespread vaccination of cattle against Escherichia coli O157 could vastly decrease the human incidence of disease associated with this pathogen, according to a new study.

Researchers at the University of Glasgow (United Kingdom) analyzed data from Health Protection Scotland, identifying 237 human E. Coli cases that occurred between 2002 and 2004, and tested almost 13,000 cattle fecal samples, finding that 4% that were positive for E. coli O157. The most common phage types (PTs) of the pathogen found were PT 21/28, which is a supershedding strain. They also calculated that the most accurate model for predicting the presence of supershedding strains in human cases involved a threshold shedding level of 1,300 colony forming units per gram (cfu/g) of feces.

Further analysis determined that the Shiga toxin (stx2) variant is found much more frequently in the supershedding strain. Examination of transmission risk across the cattle-human species boundary showed that only these relatively rare super-shedding events contribute significantly to human risk. The researchers calculated that eliminating only the 12% of highest shedding densities through cattle vaccination would result in a 50% reduction in E. Coli in cattle and an 83% decline in human cases. The study was published online on September 10, 2013, in the Proceedings of the National Academy of Science of the United States of America (PNAS).

“Because the currently available vaccines reduce high-concentration shedding of the pathogen by cattle, which we show to heavily influence transmission across the species boundary, they should be especially effective at reducing the number of human illnesses,” concluded lead author Louise Matthews, PhD, and colleagues. “Uptake, however, is poor, with the vaccine reaching less than 5% of the market—a likely consequence of the fact that currently farmers would bear the cost of vaccination but receive no direct perceived benefit, because the cattle harbor the organism without succumbing to clinical disease.”

E. coli O157 is an uncommon but serious cause of gastroenteritis, and is also noteworthy because a few, but significant, number of infected people develop hemolytic uremic syndrome, which is the most frequent cause of acute renal failure in children in the Americas and Europe. Prevention of E. coli O157 is especially important since once an infection has been established, no therapeutic interventions are available to lessen the risk of hemolytic uremic syndrome developing. Costs associated with E. coli O157 in the US alone have been estimated to be USD 600 million annually.

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