A middle-aged Iowa resident who recently traveled to West Africa has died from Lassa fever, Monday.

"I want to assure Iowans that the risk of transmission is incredibly low in our state," Dr. Robert Kruse, state medical director of the Iowa Department of Health and Human Services, said in a news release. "We continue to investigate and monitor this situation and are implementing the necessary public health protocols."

The Centers for Disease Control and Prevention and local public health partners are working to identify anyone "who may have been in close contact with the patient, out of an abundance of caution, for monitoring," the release added.

What is Lassa fever?

Lassa fever is a virus that is mostly found throughout Sub-Saharan Africa. It is spread by West African multimammate rats, which are currently the only type known to carry Lassa virus, health officials say.

The viral illness can come on quickly once someone is infected, with an incubation period of between two to 21 days, the .

In the past 55 years, there have been only eight travel-associated cases of Lassa fever reported in the U.S.  In 2015, a New Jersey man died after being diagnosed with the virus. 

About 100,000 to 300,000 cases of Lassa fever occur in West Africa each year, and about 5,000 people die from it, according to the CDC. 

How is Lassa fever spread?

People can get Lassa fever by having contact with infected rats or their saliva, urine or droppings, which may happen through contaminated food or household items.

Infection can also spread between people after contact with body fluids of an infected person. It is not spread through casual contact, such as hugging, shaking hands or sitting near someone.

"People with Lassa fever are not contagious until after their symptoms begin," the CDC notes.

The  system, where the resident was treated, said the patient was cared for in its Special Pathogen Unit, which is a contained unit designed to safely handle infectious diseases, and assured the public that the hospital "remains a safe place to receive care."

The CDC said the person was "not sick while traveling so the risk to fellow airline passengers is extremely low."

While person-to-person transmission has not been previously reported in the U.S., the CDC does urge  for viral hemorrhagic fevers like Lassa virus.

Lassa fever symptoms

While Lassa fever can be deadly, most people experience only mild symptoms, including slight fever, feeling tired and weak and headaches. Those general symptoms are similar to many other conditions, and health officials say most people with mild cases are never diagnosed.

About 1 in 5 people infected will develop a severe case of the disease, WHO says.

Some people may develop bleeding, vomiting, difficulty breathing, facial swelling and pain in the back, chest or stomach. 

The overall case fatality rate for the disease is about 1%, "but can reach 15% or more among patients hospitalized with severe presentation," according to WHO.

Health officials say treatment options may include an antiviral drug called ribavirin, which is most effective if given early on, and supportive therapy like painkillers and rehydration to help relieve symptoms.