FREEPORT – Dr. Meryl Nass’ phone has been ringing like crazy since a rare case of respiratory anthrax was confirmed in Florida.

Nass, an internist with a private practice, is an expert on the disease and has been swamped by calls and e-mail messages from people concerned about it. She’s also been a favorite target of media seeking information on anthrax.

And what has been her most important message?

“This is a very rare disease. Yes, it’s often a deadly disease, but you have to breathe in an enormous number of spores,” Nass said.

Ingesting the spores can cause illness, but the most serious form – fatal in 90 percent of cases when not treated quickly – occurs through inhalation, she said.

While it’s not known just how many spores must be inhaled to contract anthrax, it is more than 50,000, Nass said. She said that people have had exposure to spores every day without getting inhalation anthrax.

Only 66 people of the 1 million residents of Sverdlovsk, in the former Soviet Union, died after a large release of anthrax from a bioweapons factory in 1979, she said. No one in the town received any treatment.

But there still are a lot of unknowns about the anthrax bacteria. It’s not known how many strains of anthrax exist or whether the vaccine would be effective if it were widely available to the general public, Nass said.

“The science is sort of in the dark ages,” she said. “Only in the last three to five years has modern science been applied to its study.”

Nass believes the vaccine offers a modest level of protection and depends on factors such as the strain and the level of exposure.

The most recent vaccine was 95 percent effective for monkeys, but hasn’t been tested in humans. An earlier version was found to be about 70 percent effective in humans.

Part of the difficulty with developing a vaccine, she said, is that a strain can be made resistant to it or to antibiotics – though that is not a simple task.

“Vaccines can’t keep up. That’s the number one message,” she said. “For biological weapons, you have to prevent them from happening.”

The manufacture of large quantities of anthrax is difficult, she said. And if someone were able to create a weapon with anthrax, the disease would still be difficult to contract, she said.

“Once the spores hit the ground, they pretty much stay there,” said Nass.

If exposure occurs, antibiotics can be effective – before symptoms develop – in keeping the disease from spreading to more people, she said.

But despite the low risk of contracting anthrax – particularly in a sparsely populated place such as Maine – Nass has become increasingly concerned about the threat of biological weapons.

“I’m more worried than I was two weeks ago,” she said. “I don’t expect it [here], but then I never expect anything.”