The number of farms confirmed to have been hit by the new strain of the parasite theileria has doubled in the last month - and it's now widely spread throughout the middle-and-upper North Island.
There are cattle infected with theileria orientalis ikeda in 213 farms.
The Ministry for Primary Industries says a third of cattle on an infected farm typically become anaemic and the fatality rate is 1.6%.
Affected cattle require blood transfusions and treatment with a powerful drug which means withholding periods of 35 days for milk and 140 days for meat apply.
And any bobby calves born to an infected animal or which drank milk from one cannot be sent to slaughter.
The new strain of theileria, which is spread by ticks and was first detected last year, is now widespread throughout Northland, Auckland and Waikato.
Cases have also been confirmed in Reporoa, Eketahuna, Taumarunui, Whanganui, Bay of Plenty and Gisborne.
The Ministry says it didn't expect theileria to spread so rapidly over winter.
It says this winter was the warmest on record - with 9 degrees Celsius higher than average temperature - and that this may have contributed to a high tick survival rate.
The new strain of theileria has been found as far south as Canterbury.
Steffan Browning, the Green Party's agriculture spokesperson, is worried the Ministry for Primary Industries doesn't have the resources to cope with theileria orientalis ikeda and isn't doing enough to try stop its spread.
He says bio-security incursions such as this need to be eradicated rather than the current strategy of treating the symptoms.
In a statement the Ministry says its testing laboratory is currently coping with the increased workload created by the theileria ikeda incursion - and denied it is overwhelmed.
