A middle-aged woman in South Carolina has contracted the state's first case of human rabies in more than 50 years, health officials said on Friday.

"There are only about one to three cases of human rabies each year in this country," said Dr. Eric Brenner, epidemiologist with the state Department of Health and Environmental Control's Bureau of Disease Control.

"Tragically, rabies almost always ends in death," he said in a statement.

Brenner said health officials believe the woman likely was bitten by a bat that entered her home a few months ago.

"The rabies virus travels slowly through the body until it reaches the brain and central nervous system and produces serious initial symptoms including headache, difficulty swallowing, seizures, anxiety, agitation and confusion," he said. "Most patients die within a few weeks after the onset of these symptoms."

Federal medical privacy laws prevent the department from releasing any more information about the patient or her condition, said Health and Environmental Control spokesman Jim Beasley.

The woman lives in Sumter County, in the middle of the state, officials said.

Bites from rabies-infected bats are one of the most common way humans are exposed, Brenner said. Raccoons, foxes, skunks and other wild animals, as well as unvaccinated dogs and cats, can transmit rabies through their saliva into a bite wound.

South Carolina law requires all dogs, cats and ferrets to be vaccinated against the rabies virus.

The agency said it will investigate to determine if anyone else might have been exposed to the virus. Person-to-person transmission of rabies has not been documented, with the exception of special circumstances in medical settings, Brenner said.

The last cases of human rabies in South Carolina were in December 1959, when an elderly Florence County man was bitten by a dog, and in March 1958 when an elderly Clarendon County woman was bitten by a fox, Beasley told Reuters.