Some 970 dairy and beef farms have been affected by the blood-borne parasite theileria ikeda - and the number of affected herds in the North Island has risen by 12 percent the past month alone.
The latest Ministry for Primary Industries update shows that 116 new herds have been affected in the last month - on average, 29 new herds per week.
The parasite was first detected in Northland in 2012, and some people believe the parasite arrived in New Zealand through imports of Australian cattle.
New cases traditionally spike in spring, when the pasture ticks which spread the parasite thrive.
Theileria ikeda makes cattle anaemic and lethargic and kills about 1 percent of the animals it infects. However, on the hardest hit farms up to 15 percent of cattle have died.
The ministry said most of the new cases since September have been on dairy farms and concentrated around the Waikato and Auckland regions, although the outbreak has been moving into Bay of Plenty, East Cape, Manawatu and Taranaki.
A veterinarian says the agricultural sector is getting better at managing the parasite. Franklin Vets managing director Mark Hosking said theileria ikeda was rampant in South Auckland and Waikato last year, but now herds there are building up immunity.
"Most of the infection we've seen this year in our region from Hamilton through to Auckland and across the Hauraki Plains is new herds entering the regions, so naive (unexposed) animals haven't come across the disease before moving into our area and getting hit then," he said.
"Outside of our area, we are seeing progression of the disease cross over into the Bay of Plenty and further down towards Taranaki, as it moves through in an infection spread. But we've probably seen only about 20 percent of the cases that we saw last year in our region."