The U.S. Centers for Disease Control (CDC) announced Friday morning that a Maryland patient who died of rabies caught the disease by way of a 2011 organ transplant, not by an animal bite. According to CBS News, the Maryland Department of Health and Mental Hygiene began investigating the case after the patient died earlier this month of what proved to be transplant-related rabies.

Situations like this are "extremely rare," the CDC said in a statement, but the patient was one of four people who received organs from a donor who passed away last year at a health care facility in Florida. Organs that are being transplanted are checked for common blood-borne diseases like HIV and hepatitis, but if rabies is not suspected as a cause of death, doctors don't check for it.

"If rabies is not clinically suspected, laboratory testing for rabies is not routinely performed, as it is difficult for doctors to confirm results in the short window of time they have to keep the organs viable for the recipient," said the CDC's release.

"Organ screening is designed to ensure safe and successful transplantations," the organization said. "The benefits from transplanted organs generally outweigh the risk for transmission of infectious diseases from screened donors."

The other three recipients of organs from the infected patient have been contacted by health officials and started on rabies vaccines. The CDC is working with health officials in each of the states affected, as well as with those who have had close contact with the transplant recipients.

Rabies is rare in humans. The disease poses the most risk to household pets. Some 40,000 people in the U.S. who work with animals or otherwise risk infection are immunized against the disease every year. Typically rabies has an incubation period of one to three months, but the transplant cases are consistent with sore reports of longer incubations.

According to the CDC's rabies information page, "The first symptoms of rabies may be very similar to those of the flu including general weakness or discomfort, fever, or headache." The disease then progresses into symptoms of brain malfunction, anxiety, confusion and agitation followed by insomnia, delirium, hallucinations and abnormal behavior.

Once the disease has progressed into it the second stage of symptoms, it is nearly always fatal.

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