The heartbreak remains.

Three months after her Labrador retriever, Tandy, died from a rare illness that strikes dozens of Minnesota dogs yearly, Jane Heinks covets the memories of her first hunting dog and family companion.

"She was just a wonderful dog," said the 48-year-old from New Brighton, still choked up with emotion. "She was lightning in a bottle. Everyone loved her. Her death absolutely broke my heart."

With thousands of hunting dogs heading afield this fall, how and why Tandy died is a lesson for others to be aware of the little-known disease that struck down the healthy 7-year-old dog in her prime.

Tandy died of blastomycosis, caused by a naturally occurring fungus in moist soil. It has sickened or killed about 900 Minnesota dogs during the past 13 years. Of the 644 cases that state officials were able to investigate, 354 dogs recovered and 290 died or were euthanized.

Blastomycosis also infects about 30 humans a year in Minnesota, killing an average of three. It does not spread from dog to dog or dog to human.

"If it's caught early before the disease has become widespread, the prognosis is good for both dogs and humans," said Dr. Joni Scheftel, public health veterinarian with the Minnesota Department of Health.

Mystery surrounds the disease. Many dogs and people likely come in contact with the fungus without suffering serious symptoms. Officials don't know why it seems to strike some dogs but not others.

The fungus tends to grow in rich organic soil along waterways, and most of the state's cases have occurred in the north, especially in Itasca and St. Louis counties.

"You know how many dogs are sniffing around the waterways of northern Minnesota," Scheftel said. "The vast majority that are exposed have no symptoms.

"We really don't know what factors trigger it. We see clusters of cases in one area one year, and then won't see any cases in that area. It's almost as if the stars have to line up."

It's not known if drought or wet cycles are factors. So far this year, dog and human incidences are down, Scheftel said.

Unlike Lyme disease, heartworm or rabies, there is no vaccination to prevent canine blastomycosis.

"There is no prevention," said Dr. Jane Armstrong, professor at the University of Minnesota College of Veterinary Medicine.

Dog owners should be aware of the symptoms, which usually don't appear until two or three weeks after exposure, sometimes making it difficult to know where animals contracted the disease.

"The usual signs are fever, coughing or difficulty breathing, lack of appetite and skin lesions that drain and don't heal," Armstrong said. Lethargy is another sign. The disease also can cause blindness and lameness.

When it progresses, it attacks lung tissue and, in the advanced stage, is difficult to treat.

"They die of an overwhelming infection," Scheftel said.

Antifungal medication also is expensive, often $1,000 or more. Of the 290 dogs that died from blastomycosis, 180 were euthanized because of a poor prognosis and/or the cost of the therapy, according to the Health Department.

"The cost has come down in the last five years," Scheftel said.

For Heinks and her husband, Mike, and three kids, blastomycosis was a nightmare.

"I'd never heard of it," she said. "And Tandy didn't exhibit normal symptoms."

The family went to their farm in Otter Tail County last April, where Heinks believes the dog might have picked up the fungus. Tandy suffered a grand mal seizure last April. "She didn't have open sores or a cough; our vets thought she might be developing epilepsy or a brain tumor," Heinks said.

Then Tandy went lame and developed sores in her mouth and loose teeth. In early June, an X-ray showed her lungs badly infected, and she was diagnosed with blastomycosis. She was given antifungal medication, but it was too late.

"The next day she walked outside to her favorite spot in the yard, laid down and died," Heinks said. "She had a great life, but she was robbed. It still breaks my heart."

Tandy was buried on a hill overlooking a duck pond at the family farm.

"She lived to go duck hunting," Heinks said. "We were blessed for seven years. She was everything you could want -- good-looking and a beautiful temperament. She was a great dog.

"She showed us how good having a dog can be."

Heinks said the family eventually will get a puppy, another Lab.

With luck, a dog like Tandy.

Doug Smith •; Twitter: @dougsmithstrib