After the first rabbits died, they threw away the rabbit food and switched to organic greens as well as switching from tap water to bottled.
The sick rabbits were isolated but the virus still spread, eventually killing all but one adult and six baby rabbits, which were still immune to the virus due to their young age.
The rabbits displayed few symptoms and died very quickly, mostly overnight, Mrs Brown said.
"They were healthy one minute and dead the next.
"I never imagined that this would happen, and in such a short time. We went from having oodles to just these guys."
The park is a memorial to Alexis Still and Chrisjan Jordaan, who died jumping from the burning basket during the Carterton balloon crash, landing in the Browns' paddock.
It is home to a variety of animals, including pigs, chickens, parrots, bearded dragons, blue-tongued skinks and ponies.
With their 5-month-old grandson in Wellington Hospital with an undiagnosed ailment, the loss of the rabbits felt like a double blow, Mrs Brown said.
The couple did not know what killed the rabbits until they paid for an autopsy, which confirmed it was rabbit calicivirus disease (RCD), a highly infectious, often fatal viral disease that was introduced illegally into New Zealand in 1997 in an attempt to curb wild rabbit infestations.
Mrs Brown urged owners to be aware of the virus and get their rabbits vaccinated.
"I think it's about $36 but even the cost of replacing one rabbit, and the heartache - you can't really replace them - it's not the same."
Veterinarian at South Wairarapa Veterinary Services Richard Kirton said he was aware of another owner who had lost three or four rabbits to the disease this week, and the clinic's laboratory had advised there had been other cases in the Hutt and Taranaki.
While the virus is generally thought to be spread by direct contact with infected rabbits, it could also be spread through contact with infected bedding, water bowls and hutches, Mr Kirton said. "It can be windborne as well, but generally it's thought to be rabbit-to-rabbit or infected urine or faeces."
The disease has a mortality rate approaching 100 per cent.
Rabbits were an increasingly popular pet and it was better to vaccinate than to have an awkward conversation with the children, he said. "Outbreaks like these are a good warning to owners that even if they just have one, they still need to take precautions. It's better than having to explain to the children why the rabbit has died. Most parents don't want to have to go through that."
Rabbits in urban areas could be infected. "Even if you are living in urban Masterton, there's parks and they could still be in contact with it. If there's rabbits around, the risk is there."
