A New Jersey man died Monday evening after been diagnosed with Lassa fever — a frightening infectious disease from West Africa that is rarely seen in the United States, a federal health official said.

The man recently returned from Liberia, arriving at New York City's JFK International Airport on May 17. He grew critically ill after his return, suffering from multiple organ failure, said Dr. Tom Frieden, director of the U.S. Centers for Disease Control and Prevention in Atlanta.

Health officials said they don't think the case is cause for public alarm. Lassa fever is not spread through casual contact. About a half dozen other cases have been diagnosed in travelers from West Africa in the past, and none of them ever spread the illness person-to-person, Frieden said.

But as a precaution, the CDC and New Jersey health officials are trying to track down and monitor anyone the man was in contact with during the past week, including health workers at two New Jersey hospitals and people who sat close to him on his recent flight from Morocco to New York.

The illness is commonly seen in West Africa, in some of the same countries struck by the recent Ebola epidemic. This last confirmed case of Lassa fever seen in a traveler returning to the United States was in Minnesota last year. The one before that was in Pennsylvania in 2010.

Generally speaking, Lassa fever is far less likely to be fatal than Ebola and less likely to be spread from person to person. About 80 percent of cases are mild. But in severe cases, patients can suffer fever, vomiting, organ failure, shock and even bleeding from the eyes, nose and gums. It's fatal in about 1 percent of cases. Sometimes, those who survive are deaf for the rest of their lives.

Like Ebola, it can spread through contact with blood, feces or vomit of an infected person. In West Africa, Lassa virus is carried by rodents and transmitted to humans through contact with urine or droppings of infected rodents.

CDC officials declined to give the name or identifying information about the man, other than to say he frequently traveled to Liberia on business and had worked in the mining industry. CDC officials on Monday also declined to name the New Jersey hospital where the man first went for care, or to a second New Jersey hospital where he was to have been treated with ribavirin, an antiviral medication given intravenously. But officials say the patient died before he could receive the ribavirin, noting the hospital was securing the medication at the time of the man's death.

The patient had no symptoms during the flight, but a day later went to a New Jersey hospital suffering from a sore throat and lethargy.

Hospital officials said they had asked the man about his travel history and that he did not say he had recently been to West Africa, CDC officials said.

Three days later he had returned to the hospital with more severe symptoms. He was transferred to the second hospital Saturday. On Monday, CDC lab tests of the patient's blood confirmed Lassa fever.

The CDC plans to send a special response team including a Lassa fever expert and specialists in occupational safety and waste management to the second hospital Tuesday.

Health officials regularly note that exotic illnesses are only a plane ride away.

"We expect to see Lassa fever and other infections like this. Because of Ebola, we're now better prepared to deal with it," Frieden said.

Lassa fever was named after a Nigerian town where Western-trained doctors first noted it in 1969. An estimated 100,000 to 300,000 infections occur in West Africa each year, including about 5,000 deaths. In some areas of Sierra Leone and Liberia, 10 to 15 percent of people admitted to hospitals every year have Lassa fever.