'Even a well-managed and relatively small foot-and-mouth outbreak would take something like 10 billion (new Zealand) dollars (US$7.2 billion; euros 5.7 billion) off economic growth and basically wind back the economy for a year to 18 months.'

Officials Report No Sign of Foot-and-Mouth Disease on New Zealand Farms

More than 20,000 New Zealand farm animals continue to show no sign of foot-and-mouth disease -- nearly a week after a scare over the virus became public, officials said Sunday.

With no animals exhibiting any symptoms, officials believe an extortion letter claiming that feed hay had been infected with the disease on Waiheke Island was a hoax.

The nation's Agriculture ministry said foot-and-mouth -- which is highly contagious but seldom fatal to livestock -- had not been found anywhere in the country, including at a second location where a letter to Prime Minister Helen Clark last Monday threatened a further release.

Police, backed by Australian police threat assessment experts, believe the letter poses a "low level of threat," reinforcing the view that it is a hoax.

Authorities continue to take the threat seriously and will test the island's 18,000 sheep and 2,500 cattle every 48 hours till May 23, the director general of the Agriculture Ministry, Murray Sherwin, said.

A foot-and-mouth outbreak would devastate New Zealand's tourism and farming industries -- the main pillars of the economy and major earners of foreign exchange. International markets would probably ban mutton, beef, wool, cheese and other farm products from New Zealand, while travel restrictions imposed within the country would hurt tourism, analysts say.

"Even a well-managed and relatively small foot-and-mouth outbreak would take something like 10 billion (new Zealand) dollars (US$7.2 billion; €5.7 billion) off economic growth and basically wind back the economy for a year to 18 months," Sherwin said.

Vet Phillip Brown said the checks would go on every 48 hours.

"What we are doing now is a straight visual exam of everything," he said. Earlier all animals were temperature checked for first signs of the disease.

New Zealand has alerted some 50 trading partners to the scare, but so far none have severely curtailed the country's farm exports.

Mexico, which had held up dozens of containers of meat and dairy products in the wake of the scare, released the containers late Saturday.

The virus' incubation period is normally 4 to 7 days, but it can take up to two weeks for symptoms to appear.

Foot-and-mouth affects cloven-hoofed animals such as cattle, sheep and pigs, causing sores, blisters and fever, but it is rarely fatal in livestock and harmless to people.