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Lassa Fever Carries Little Risk to Public, Experts Say

A sample of the virus that causes Lassa fever as seen through a transmission electron microscope.Credit...Ami Images/Science Source

The report that a man who traveled from Liberia to New Jersey had died on Monday from the viral illness Lassa fever is another reminder that infectious diseases can hop continents and elude detection by health care workers who do not know a patient’s travel history.

Following is information about the disease:

WHAT IS LASSA? Lassa, like Ebola, is a viral hemorrhagic fever. But Lassa is from a different family, not as contagious and nowhere near as deadly as Ebola.

IS IT CONTAGIOUS? Lassa does not spread easily from person to person, and health officials say there is little or no risk to the public. Several Lassa cases have occurred in the United States, all in travelers from other countries. There has never been person-to-person transmission in the United States, according to the Centers for Disease Control and Prevention.

HOW DO PEOPLE GET IT? In West Africa, where Lassa is common, people usually contract it from rat droppings or urine, or from catching and preparing rats to eat. Person-to-person spread does not occur through casual contact, experts say; transmission requires direct contact with a sick person’s blood, bodily fluids or mucous membranes, or sexual contact.

Person-to-person transmission of Lassa is common in health care settings like some in West Africa, where proper personal protective equipment is lacking, the C.D.C says. The virus may be spread by contaminated medical equipment, such as reused needles.

WHAT ARE THE SYMPTOMS? The incubation period — the time it takes to get sick after being exposed to the virus — is one to three weeks. Most people, about 80 percent, have only a mild, flulike illness with a slight fever, headache and fatigue. But some people become severely ill, with hemorrhaging (in the gums, the eyes, the nose and other places), breathing trouble, vomiting, facial swelling, pain in the chest, back and abdomen, and shock. Some develop neurological problems, including hearing loss, tremors and encephalitis. The antiviral drug ribavirin can reduce the severity of the disease, especially if given early.

IS IT DEADLY? About 100,000 to 300,000 cases of Lassa fever, and 5,000 deaths related to the illness, occur in West Africa each year. Over all, about 1 percent of people with Lassa die from it. In pregnant women, the disease often kills the fetus. Women themselves are particularly vulnerable in the third trimester of pregnancy and have high death rates, according to the C.D.C.

A version of this article appears in print on  , Section A, Page 17 of the New York edition with the headline: Another Illness From Afar, but This One Isn’t as Serious . Order Reprints | Today’s Paper | Subscribe

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