The risk to humans of salmonella brandenburg has increased as the disease spreads in South Island sheep flocks and dairy herds.
The disease has rapidly taken hold in Southland dairy herds and dairy farmers have a nervous wait to see if the epidemic will extend to Taranaki and Waikato this winter.
Salmonella brandenburg aborts lambs and kills sheep.
Its human victims can be laid low for up to six weeks with severe diarrhoea, stomach cramps and fever.
Veterinary adviser Roger Marchant said that even after recovery, sufferers could have relapses for several months.
"It's not a pleasant illness ... The infection rate in humans has been climbing rapidly."
Children, the elderly and people with immune-system problems were the most vulnerable.
Even veterinarians, who took careful precautions, had been infected.
"In one practice, three out of six veterinarians were struck," Mr Marchant said.
The vets were working with aborting cows and despite scrupulous attention to hygiene, the large number of disease organisms proved overwhelming.
Mr Marchant said the disease would persist in soil.
Sheep yards were a common source of infection, along with farm families who picked up the infection from handling aborted lambs and sick ewes.
The epidemic's spread into cattle had coincided with a surge in dairying in Canterbury, Otago and Southland.
Southland, where salmonella brandenburg had spread most rapidly among animals, also accounted for nearly 40 per cent of human cases last year.
Other veterinarians said farmers and farm workers should pay closer attention to hygiene when salmonella brandenburg was detected in their animals.
That was even more important for dairy workers who came into daily contact with the animals.
Safety measures could include using disposable gloves when dealing with infected animals, burning or burying aborted foetuses and placenta, culling aborting ewes and killing scavengers, such as dogs and black-backed gulls.
For personal hygiene, farmers were advised to use an effective disinfectant where an abortion had occurred.
They should clean and disinfect vehicle tyres and footwear, carefully wash hands before eating or smoking and remove contaminated clothing before entering the house or children's play areas.
There were fears that the disease could erupt in the North Island after an animal health laboratory isolated the salmonella strain from samples taken from calves at three North Island dairy farms.
Until 1999, the disease had been confined to sheep properties from mid-Canterbury south.
But last year, the number of cases on dairy farms started to climb dramatically.
In dairy herds, the disease causes diarrhoea and abortions in cows and diarrhoea, dysentery and deaths among young calves.
Veterinary pathologist Gary Clark, who works at Mosgiel, near Dunedin, said the dairy farm cases were probably caused by increased environmental contamination as the disease spread among sheep properties.
It had also cropped up in young calves in Central Otago, brought in from areas where the disease was endemic.
"This illustrates the dangers of introducing the disease into new areas with infected stock," Mr Clark said.
More than 60,000 dairy cattle were expected to be moved around the South Island over the next two months. The upsurge in stock movement would come as farmers prepared for the new dairy season starting in June.
Mr Marchant works for an animal remedy company that manufactures a vaccine partially effective against salmonella brandenburg in sheep.
But Mr Marchant said there was little information on the performance of the vaccine in protecting cattle.
A survey done by his company had shown that on farms where the disease had not occurred in the previous year, the disease rate in unvaccinated ewes had averaged 7 per cent.
In flocks with previous exposure it was 4.82 per cent, said Mr Marchant.
"The most vulnerable flocks are those with no previous exposure."
- NZPA
Farmers at risk as salmonella strain spreads
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