Three people died of rabies (search) after receiving infected organs from the same donor in what the government says are the first documented cases of the disease being spread through organ transplants.

Federal agencies are now looking into whether transplant (search) organs should be screened for the rabies virus.

The lungs, kidneys and liver of an Arkansas man who died in May were donated to four patients in Texas, Oklahoma and Alabama, the Centers for Disease Control and Prevention (search) said Thursday. Three of them died of rabies; the fourth died of complications during surgery, the CDC said.

The donor had shown no symptoms of rabies before his death from a brain hemorrhage, said Dr. Mitchell Cohen, director of the CDC coordinating center for infectious diseases.

"We are learning as we go — this has never happened before," Cohen said.

While these are the first known cases of rabies being spread through donated organs, at least eight people have contracted the virus through cornea transplants, the CDC said.

Rabies testing is not routinely done on U.S. organ donors, although there are routine screenings for other diseases, including hepatitis B and C, HIV and syphilis. Rabies has not been found in donated blood.

The CDC said it is working with health officials in the four states to determine whether other people who had contact with the organ recipients or the donor need treatment for rabies.

Rabies cases in humans are extremely rare in the United States. On average, only one or two people die from the disease each year, according to the CDC. There were no human cases in 2001, the latest year for which figures are available.

The few people who contract rabies usually get it after being bitten or scratched by an infected bat.

In the transplant-patient deaths, the virus could have been in the nerves of the transplanted organs, Cohen said.

Symptoms of rabies can include fever or headache, and later, confusion, sleepiness or agitation. People usually start to show signs up to three months after being infected.

Last fall, scientists discovered the West Nile virus could spread through blood transfusions and organ transplants. That led to the screening of blood donations for the mosquito-borne virus.