There is a warning that the cattle disease, Theilaria, could be here to stay, as the number of reported cases on the rise. It causes anaemia in cows and is spread by ticks.
Signs in cattle include lethargy, low appetite and reduced milk production.
The Veterinary Association's Dairy Cattle Society president says 45 new farms have reported Theilaria in recent weeks, joining about 500 others already with it.
Jenny Weston said because Theilaria is not a notifiable disease, it is hard to track actual numbers because vets and farmers are becoming more confident in spotting the disease without having blood samples taken.
"We are expecting it to become an endemic disease in New Zealand which means it will be always here at a certain level.
"We have had what you would categorise in the past an epidemic because we didn't use to have the disease and suddenly seeing a lot more of it but we think this is something farmers are going to have to live with for the rest of New Zealand's farming history."
Dr Weston said the tick that spreads the disease probably arrived in New Zealand about five years ago.
"Animals are always treated for ticks before they are imported but the parasite would have been in the animal's blood stream when it came to New Zealand and then that has lead to our tick population becoming infected.
"This particular strain of Theilaria which is causing all the disease we think probably came in about four or five years ago. We have had a different strain of Theilaria for 20 or 30 years in New Zealand which hasn't caused many significant animal health problems up until now and was predominantly seen only in Northland."
Ms Weston said vets have learned much about Theileria over the past couple of years since significant outbreaks of the disease started to occur.