Because New Zealand does not have the ticks that typically spread the disease it is thought to be very low risk that the mare has transferred it to another horse, but because New Zealand cannot be certified as now being free of piroplasmosis Australia has suspended flights of New Zealand horses to Australia.
Any long-term ban on horses crossing the Tasman for both racing and breeding purposes would be a disaster but that seems extremely unlikely.
However, until the Ministry of Primary Industries has investigated the positive and reported back to Australian authorities, the flights will remain grounded.
"At this stage it is really a trade issue more than a health issue that MPI are trying to get to the bottom of," said Dr Ivan Bridge, chairman of the New Zealand Equine Health Association.
"Australia requires us to have no piroplasmosis in the country for at least three years.
"MPI can't sign off on that at present.
"We have not had any clinical piroplasmosis in New Zealand and we don't believe that the tick that we have in New Zealand is capable of transmitting it.
"So what might look like a problem now because we can't fly horses right at the moment might be a two out of 10 problem next week and not an issue heading forward.
"Basically horses get tested for this and a range of other diseases before they fly anyway, which is how this mare was diagnosed. So we can't and won't be sending any horses to Australia or anywhere else with any issues because it would show up in those tests.
"But that is if it even spread from this one mare, which would seem extremely unlikely."
With no major racing carnivals on in Australia at the moment and the breeding season still months from starting it would be surprising if a short-term ban had any great detrimental effect on the racing industry which has been hit hard by racing being shut down for over two months.
Horse racing in New Zealand returns, albeit closed to the public, next Friday for harness racing, with thoroughbred racing due back on July 3.