A man, right, working for a humanitarian group, throws water in a small bag to West Point residents behind the fence of a holding area, as they wait for a second consignment of food from the Liberian Government to be handed out, at the West Point area, near the central city area of Monrovia, Liberia, Friday, Aug. 22, 2014 during the height of the Ebola epidemic there. (AP Photo/Abbas Dulleh)

When a man returning to the United States from Liberia showed up at a New Jersey hospital earlier this week with symptoms of a viral hemorrhagic fever, public health officials feared the worst. The traveler was put in isolation and blood samples were rushed to a lab where they were tested for Ebola.

The Centers for Disease Control on Monday said the patient had died. He was not suffering from Ebola but another viral disease common to West Africa known as Lassa fever. While the disease can produce serious symptoms similar to Ebola in some patients, it's markedly different in a lot of important ways.

[In Liberia, Ebola outbreak is declared officially over]

Discovered in 1969 when two missionary nurses traveling in the region died, Lassa fever is endemic in parts of West Africa, where 100,000 to 300,000 people are estimated to be infected each year. Symptoms begin one to three weeks after the person becomes infected: fever, sore throat, vomiting, facial swelling, mucosal bleeding, possible neurological problems.

For many people, the disease is mild and there are even some people who are infected have no symptoms at all. But in about 20 percent of those infected, it can be severe and affect multiple systems in the body. The most common complication is deafness. It is fatal in 1 percent of cases.

In contrast, Ebola is fatal in 70 percent of cases without treatment.

Lassa fever is also much less contagious than Ebola. It's carried by rodents, and humans typically become infected from coming into contact with urine or droppings. The Centers for Disease Control says that the virus isn't transmitted through casual contact, although "in rare cases" it can be transmitted through direct contact with a sick person's bodily fluids or through sexual contact.

The CDC says there have been no cases of transmission in the United States and that the New Jersey incident is only the sixth case of Lassa fever in the United States. The latest one before that was in 2014 in Minnesota.

Ebola is highly contagious, transmitted through contact of bodily fluids including mucus, vomit, sweat and tears, and has led security officials in West African countries to quarantine whole towns infected with the virus.

There's an effective treatment for Lassa fever called Ribavirin. While scientists have discovered several promising vaccines and treatments for Ebola, they are still being tested.

The CDC said it's working with public health officials to track down people who may have been in contact with the man, who arrived in the United States on a flight that landed at John F. Kennedy International Airport and will monitor them for 21 days.