Waikato beef and dry stock farmers have higher rates of leptospirosis, a potentially fatal bacterial disease passed to humans through animals and infected water, according to a study in the New Zealand Medical Journal.
The farmers were probably more at risk because beef and dry stock cattle were less frequently immunised against the deadly disease, according to the report by Waikato District Health Board medical officer of health Dr Anita Bell and health population officer George Cowie.
The study, done over seven years, found the Waikato has one of the country's highest annual rates of notified cases of the infectious disease, with the majority coming from the Waitomo district.
In the study 97 cases of leptospirosis, which can also cause life-threatening complications such as meningitis or kidney failure, were notified in the Waikato District Health Board region between January 1, 2004 and December 31, 2010.
Of those, 90 had direct exposure to animals and 19 to water, with 85 of the cases exposed through occupation and five through overseas travel.
The cases were more likely to be associated with working age, European males who had close contact with animals in their working environment, and the three largest represented occupational groups effected were dairy farmer, farmer or farm manager, or meat processor.
Those listed as farmer or farm manager, the largest group at risk, included livestock and mixed livestock farmers, beef farmers, and sheep farmers.
New Zealand dairy herds had been immunised against three types of the disease since the 1980s, resulting in a major reduction in the incidence of leptospirosis in dairy farmers, but dry stock herds were typically not immunised, the report said.
Of the 11 districts covered in the study, Waitomo had the highest average annual rate of 30 cases per 100,000, followed by Ruapehu with 23 per 100,000.
The lowest effected area was Hamilton.
There was a higher ratio of dry stock herds to dairy herds within the Waitomo and Ruapehu districts according to data from the Animal Health Board.
Dr Bell said the cases were "the tip of the iceberg" and sufferers were often fit men who ended up in hospital requiring an extended recovery time.
A Te Puke meatworker died after he caught the disease at work in February 2005 and former British rowing champion Andy Holmes, who won Olympic gold medals with in 1984 and 1988, died in October 2010 from leptospirosis.
Also known as Weil's syndrome, leptospirosis can also be caught through water or soil that contains the urine of infected animals.
Symptoms range from a mild flu-like illness to complications such as meningitis, liver damage causing jaundice, and renal failure.