AgResearch scientists are searching for on-farm sources of an infection that can be deadly in children and stop exports of raw ground beef from New Zealand to the United States which are worth $1.6 billion a year.

A recent New Zealand Food Safety, Science and Research Centre (NZFSSRC) report highlighted a marked increase in hospitalisation rates for campylobacteriosis, yersiniosis and STEC infections, the latter associated with the serious sequelae haemolytic uraemic syndrome (the leading cause of acute renal failure in children).

The illness often requires an extended stay in hospital and occasionally involves intensive care. While the specific reasons for the increase in hospitalisation rates were unknown, the report authors highlighted a need for more research to understand the link between rural communities and STEC, particularly in rural communities in Taranaki, where health officials in the region have published warnings and started an awareness campaign after a spike in infections.

In response, the Food System Integrity Team at AgResearch conducted experiments on two New Zealand dairy farms to better understand of the ecology of the Shiga toxin-producing Escherichia coli (known as Top 7 STEC). AgResearch scientist Delphine Rapp said: “By finding the source of STEC infection on-farm, and understanding where and how the contamination is happening in the first place, we could limit the number of animals becoming infected, and that will reduce the risk of illness in humans.

“It will also help protect export access to the all-important US. The United States Department of Agriculture classifies seven particular STEC as food adulterants for which there is a zero-tolerance policy. That means whole shipments are deemed unfit for human consumption.”

The team at AgResearch conducted a raft of tests on two commercial dairy farms and have published their findings in the academic journal, Microbial Ecology.

The study evaluated environmental reservoirs, intermediate hosts and key transmission pathways that could drive the presence of STEC on pasture-based dairy herds. A total of 235 composite environmental samples (including soil, bedding, pasture, stock drinking water, bird droppings, flies and faecal samples of dairy animals) were collected from two dairy farms over two years. Molecular detection revealed a widespread dispersion of STEC key virulence genes (stx), with the greatest occurrence (> 80%) in dairy animal faeces or on surfaces of animal housing facilities. These virulence genes were also detected in approximately half of the wildlife samples analysed, at the bottom of the water troughs (13%) and in the soil of paddocks to be grazed (35%).

The team gained whole genome sequence data confirming the existence of more than one possible route for transmission to dairy animals and a high rate of transmission of STEC between dairy animals and wildlife attracted to supplementary feed. They also showed the existence of environmental reservoirs contributing to long-term persistence of STEC virulence genes.

Delphine said the findings from the paper do not offer one silver bullet solution to eradicate the infection. However, the research does provide insights into how farmers can mitigate risk. “One of the main source of transmission is by wildlife (possums, rodents and birds) so good pest control and supplementary feed managements limiting cross-contamination of feed will help. Ensuring that sediments don’t build up in the water trough over time and abiding by stand down periods after spreading from holding pond onto pastures are also viable options, both of them encouraging voluntary intake of pasture and water by animals”.

The paper abstract says: “Overall, the findings improved the understanding of the ecology of the Top 7 STEC in open farm environments, which is required to develop on-farm intervention strategies controlling these zoonoses.” The identification of the animal factors contributing to transmission among animals will be a key aspect that will need more research.

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