YuLin Zhen, Photography Editor

Last month, the Iowa Department of Health and Human Services confirmed the death of a middle-aged eastern Iowa resident from Lassa fever after he traveled to West Africa. The News spoke with three Yale experts on the science and history behind this virus and its potential impact on public health. 

Lassa fever, which was first isolated at Yale, is a rare virus that is mostly transmitted in West Africa. Those infected with the Lassa virus may experience nausea, vomiting, fever and fatigue. There are currently no treatments specifically for it, but it should not be a concern for Americans who have not traveled to Western Africa recently.

Dr. Albert Ko, Raj and Indra Nooyi Professor of Public Health at the Yale School of Public Health, told the News that Lassa fever is an infectious disease caused by a virus in the family Arenaviridae. According to Ko, its transmission is restricted to places in West Africa.

“We usually worry about viruses in this family because they can cause hemorrhagic fever,” Ko told the News. However, he specified that a majority of people who are infected are either asymptomatic or experience very mild disease.

“Around 20 percent of people infected come down with serious disease,” Ko said. “Symptoms include nausea, vomiting, high fever and fatigue. Patients can also get capillary leak syndrome, where they are leaking fluid into their lungs and other parts of their body. In some cases, people have respiratory failure or suffer from bleeding and die of shock.”

Ko noted that the degree of exposure, the type of strain that patients are infected with and other risk factors like pregnancy can lead to more severe outcomes. 

Lassa fever has a mortality rate of 1 percent, and according to the Africa Centres for Disease Control and Prevention, the mortality rate among hospitalized patients with severe infections is around 15 percent. 

Ko explained that the virus is harbored by rodents, specifically in the genus Mastomys, which is localized to West Africa. While infection arises from contact with infected rodents or their urine and feces, Ko told the News that person-to-person transmission is possible, especially within hospitals and households. 

“It is not as infections as viruses like the Omicron variant,” Ko told the News. “One of the things that mitigates the risk is that people really aren’t transmitting to other people until they develop symptoms, unlike COVID, where you can transmit before you show symptoms.”

Ko noted that this makes it easier for healthcare professionals to diagnose the virus based on travel history to West Africa in the early stages of infection and isolate the patient. 

“It’s not easy to identify because the symptoms can be very general, so you need a high clinical suspicion when someone is coming back from a place where Lassa fever is being transmitted,” said Ko. 

Dr. Ellen Foxman, an associate professor of laboratory medicine and immunobiology in the Yale School of Medicine, outlined the general mechanism that RNA viruses like Lassa use to infect patients. 

“The basic idea of a viral infection is that it’s usually genetic material — in this case RNA — surrounded by some sort of protective coat. The virus infects the cells of your body by hijacking them like a Trojan horse so that its RNA takes over the machinery of your cells to make more copies of itself,” Foxman explained. 

This makes cells into “virus producing factories,” which usually destroy the cell that is infected, causing the variety of symptoms that patients display. 

Dr. Michael Cappello, professor of epidemiology and pediatrics and department chair of the School of Public Health told the News that treatment options for Lassa fever are limited. 

“There really aren’t any particular medications or vaccines that are available. There are some antivirals that have been tried, but these are situations where there is relatively little research being done on this, and it’s very challenging to do clinical trials,” Cappello said. 

Instead, Cappello told the News that doctors focus on supportive care, which is meant to address symptoms of Lassa fever rather than the disease itself. Supportive care for severe symptoms can include mechanical ventilation or dialysis for renal failure. 

Both Ko and Cappello also noted that the School of Public Health was crucial in the discovery of Lassa fever. 

“Lassa fever was actually first isolated at the School of Public Health, five floors above me, in 

1969 by Jordi Casals-Ariet, a professor here at the time,” Ko told the News. 

The disease, after infecting three American missionary nurses in Nigeria, was sampled and sent to Yale labs. A lab technician, Juan Roman, later became infected and died in Thanksgiving of 1969, while Casals-Ariet came close to death but was injected with an antibody-containing plasma from a surviving missionary nurse. 

“With many of these unknown infectious diseases, particularly viruses, until someone figures out how to culture it, you really can’t study it particularly well,” Cappello told the News. “The work of Dr. Casals and others created the foundation upon which all of the subsequent work on Lassa fever virus has been done.”

All three experts stressed that the virus does not pose a public health risk to Americans who have not traveled to West Africa. “Cases in America are very rare. There have been less than eight travel-related Lassa virus cases in the United States in the past 55 years,” Ko said. 

Still, both Ko and Cappello identified Lassa fever as a neglected public health problem in West Africa that may be worsened with rising globalization. 

“This impacts hundreds of thousands of people in countries like Nigeria, Sierra, Leone and Liberia,” Cappello told the News. “The fact that there aren’t available vaccines, or even readily available effective medications, really puts poor countries at a particular disadvantage when it comes to managing patients who actually become severely ill.”

In general, all three experts recommended practicing general hygiene like frequent hand washing to reduce chances of sickness in general, especially during the upcoming winter season. 

The first documented case of Lassa fever occurred in 1969.