Health authorities are currently looking into the death of an individual in Iowa, which is being treated as a potential case of Lassa fever, a viral disease that is seldom encountered in the United States. This investigation comes after the person returned to the U.S. from West Africa earlier this month, and it was noted that they did not exhibit any illness during their travels. According to officials from the Centers for Disease Control and Prevention (CDC), the likelihood of infection for other airline passengers is “extremely low,” since the virus is not transmitted through casual contact and individuals are not contagious before displaying symptoms.

The patient had been receiving care in isolation at the University of Iowa Health Care Medical Center. Initial tests conducted on Monday by the Nebraska Laboratory Response Network indicated a presumptive positive result for Lassa fever. Should these results be confirmed, this case would mark the ninth documented instance of Lassa fever in travelers returning to the U.S. from regions where the disease is prevalent since 1969.

In collaboration with Iowa health officials, the CDC is working to track down individuals who may have had contact with the patient once symptoms manifested. Typical symptoms of Lassa fever are mild, generally including fever, fatigue, and headaches, although some cases may escalate to more severe symptoms such as vomiting, trouble breathing, facial swelling, or pain in the back, chest, or abdomen.

Those classified as close contacts of the patient will be observed for a duration of 21 days. State and local health officials are investigating how the unnamed patient contracted the virus, with preliminary reports suggesting possible exposure to rodents in West Africa. The Lassa fever virus is primarily transmitted by rodents, with human infection occurring via contact with the urine or feces of infected animals. Transmission between humans is infrequent but can happen through direct contact with an infected person’s blood, bodily fluids, mucous membranes, or during sexual contact.

West Africa sees an estimated 100,000 to 300,000 cases of Lassa fever annually, which contributes to around 5,000 fatalities each year.