Cattle in a dairy herd in the Awanui area north of Kaitaia have been found to be infected with bovine tuberculosis.
The infection - a major blip in the region's long TB-free status - has brought a quick response from the Animal Health Board (AHB), which has clamped movement controls on animals in the herd and is testing neighbouring herds.
Cows identified with TB in the infected herd have been withdrawn from milking. While drinking raw milk from the rest of the herd could contain an element of risk for humans, the pasteurisation milk goes through in commercial processing eliminates danger of infection.
The AHB has also started annual TB testing for cattle and deer herds within 10km of the infected property. They were formerly tested every three years.
Two dairy herds in the same area were diagnosed with TB in 2009, but AHB Northern North Island co-ordinator Frank Pavitt said yesterday diseased animals had been slaughtered and those herds had since tested clear of infection.
For privacy reasons, he declined to identify the owners of infected herds or the number of animals infected, saying there were several possible sources of the latest outbreak.
Checks on wild animals, especially possums and pigs, were under way to see if bovine TB was present in the surrounding area.
A significant number of possums and pigs had been caught around Awanui when the same process was followed after the 2009 TB outbreak, Mr Pavitt said.
While possums were the main source of TB infection in farmed cattle and deer in New Zealand, they had never been identified as a cause in Northland.
Other possible causes of infection included buying in infected cattle, or hunters introducing deer or pigs from infected areas to provide sport in the North.
The AHB together with the Northland Regional Council and Department of Conservation, fund a Northland deer recovery programme. Its hunters may help locals look for infected feral animals around Awanui.
TBfree Northland Committee chairman Neil MacMillan said while the latest Awanui infection was not good news, with the assistance of the Animal Health Board and local herd owners, the issue could be dealt with effectively.
Beef and dairy cattle farming are the mainstays of the Northland economy. The region had 275,070 dairy cows in 930 herds and 465,000 beef cattle in 2011.