"Suspicious" test results for the highly contagious cattle disease Mycoplasma bovis have been detected on two new farms in the Waimate district.

The Ministry for Primary Industries (MPI) has placed a Restricted Place Notice over the properties to stop movement of livestock. They both border farms owned by Aad and Wilma van Leeuwen, on whose properties the disease was first detected in July.

The Van Leeuwens, who are estimated to be worth about $60 million, own 16 dairy farms.

This brings to nine the number of properties infected with the disease, eight of them in South Canterbury/North Otago and one in Rangiora.

Last month MPI said about 4000 Van Leeuwen cattle worth up to $8 million would be slaughtered to halt the spread of the disease. Already a small number of cows have been culled off two properties including the lifestyle block in Rangiora.

READ MORE: MPI to slaughter 4000 cattle to stop spread of disease Mycoplasma

MPI's director of response, Geoff Gwyn said further tests to confirm the presence of Mycoplasma would be available later this week.

"We do not believe the new suspect properties represent a game changer. These farms are in the same geographical area to all known infected properties and neighbour Van Leeuwen Dairy Group farms.

The disease, which is found in most dairy producing countries, was detected for the first time in New Zealand in July.

M. bovis is highly contagious within herds but does not travel from farm to farm through airborne means. It does not infect humans and presents no food safety risk. There is no concern about consuming milk and milk products.

It causes untreatable mastitis in dairy and beef cows, pneumonia in up to 30 per cent of infected calves, ear infections in calves, abortions and swollen joints and lameness.

Gwyn said the properties had been identified through testing more than 40,000 samples of milk, blood and swabs.

"Our investigators are still building a picture of how animals on the farms could have been infected, if indeed they are, and what stock movements may have taken place onto the farms."

He said Mycoplasma was spread through close and prolonged contact between animals and through the direct movement of stock.

"The discovery of the new potentially positive properties has not changed our position on this. We do not believe there is a significant risk of disease spread across fences," Gwyn said.