A resident from eastern Iowa died on Monday from a viral illness that resembles Ebola, which was likely contracted during a recent visit to West Africa.

This person is thought to be the ninth reported case of Lassa fever in the United States in the last 50 years, according to the Centers for Disease Control and Prevention (CDC). Lassa fever is commonly spread through the excreta of rodents infected with the virus, which are prevalent in West Africa. The middle-aged resident returned from the region in early October, as stated by Iowa public health officials in a news announcement.

The CDC is currently conducting final laboratory tests after initial tests on Monday showed a presumptive positive result. The individual succumbed on Monday afternoon while receiving treatment in isolation at the University of Iowa Health Care Medical Center. Although Lassa fever presents symptoms similar to those of Ebola, experts indicate that it is far less lethal.

Officials at both the state and federal levels have stated that the risk of transmission is minimal.

“We are actively investigating and monitoring this case and implementing essential public health measures,” said Dr. Robert Kruse, the state medical director at the Iowa Department of Health and Human Services, in a statement.

Lassa fever is primarily spread through the urine or feces of infected rats. The multimammate rat, found in West Africa, is the sole known carrier of the virus. The disease has been reported in countries like Sierra Leone, Liberia, Guinea, and Nigeria. Humans can also transmit Lassa fever through blood or bodily fluids when showing symptoms.

According to officials from the CDC, initial information suggests the patient may have interacted with rodents during their trip to West Africa. Although specific details about the individual have not been disclosed, officials are working to identify others who may have been in contact with them around the onset of symptoms.

Individuals who had close contact with the infected person will be monitored for a period of three weeks, according to the CDC. The virus has an incubation period ranging from two to 21 days.

Prior to this incident, eight Lassa fever cases had been reported in the U.S. following travel to areas where the disease is endemic. According to the African Centres for Disease Control and Prevention, approximately 5,000 people die from Lassa fever annually in West Africa, with total annual cases ranging from 100,000 to 300,000. Most individuals experience mild symptoms or none at all, making fatalities quite rare, experts say.

What are the symptoms of Lassa fever?

The symptoms of Lassa fever typically develop gradually. It is considered much less deadly than Ebola or the Marburg virus, another severe hemorrhagic fever. Treatments include the antiviral medication ribavirin.

Symptoms may include fever, general weakness and discomfort, followed by headaches, sore throat, muscle or chest pain, nausea, vomiting, diarrhea, cough, and abdominal pain, as noted by the African health surveillance office. Severe cases may lead to facial swelling, fluid accumulation in the lungs, bleeding from the mouth, nose, genitals, or gastrointestinal tract, and low blood pressure.

25% of survivors experience hearing loss, although most regain their hearing in the months following infection. Death typically occurs within two weeks after the appearance of symptoms, according to the African health monitoring agency.

The first recognized cases of Lassa fever in the United States were documented in 1969. The disease derives its name from the Nigerian town where it was first identified following the deaths of two missionary nurses, as reported by the U.K. Health Security Agency.

Cases tend to occur during the dry season from December to April, coinciding with the breeding cycle of the multimammate rat during the wet season, as per the World Health Organization.