Louisiana Already Has Its Own Hantavirus. Here’s How to Protect Yourself.

LAFAYETTE, La. — The hantavirus outbreak aboard the cruise ship MV Hondius has put the virus on the front page for the first time in years, and with it has come a straightforward question from people in Louisiana: is this something we need to worry about here?

The Andes virus strain on that ship is not a local threat. Its rodent host does not exist in North America. But Louisiana has its own hantavirus, and it has been circulating in this state for decades.

It is called Bayou virus. It was first identified in Louisiana in 1993, the same year the better-known Sin Nombre virus triggered a national outbreak in the Southwest. It lives in the marsh rice rat, a semiaquatic rodent common throughout the coastal wetlands, bayous, and freshwater marshes of the Gulf South. Research published in February 2025 in the CDC’s Emerging Infectious Diseases journal confirmed two new Louisiana cases from 2022 and 2023, with genetic sequencing indicating the virus is broadly distributed in rodents across the state.

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What Bayou Virus Is

According to the Louisiana Department of Health, Bayou virus causes hantavirus pulmonary syndrome with an unusual clinical profile. In addition to the severe respiratory distress typical of HPS, Bayou virus infections are also marked by renal insufficiency and intra-alveolar hemorrhage. Those features are more commonly associated with the hemorrhagic fever strains found in Europe and Asia, making Bayou virus one of the more clinically unusual hantavirus strains in North America.

It is also one of the deadliest. Wikipedia’s entry on Bayou virus, drawing on peer-reviewed sourcing, notes that HPS caused by Bayou virus carries a case fatality rate of almost 50%. The Andes virus strain generating international headlines right now has a confirmed case fatality rate of 38% in this outbreak.

Bayou virus now represents the second most common hantavirus in the United States, behind only Sin Nombre virus. Its natural range extends into Texas, Georgia, and other southeastern states, but Louisiana is where it was first identified and where it has been most closely studied.

Where the Virus Lives in Louisiana

The marsh rice rat, known scientifically as Oryzomys palustris, is the primary reservoir for Bayou virus. It is a medium-sized, gray-brown rodent that lives in saltwater and freshwater marshes, swamps, and wetland areas throughout the southeastern United States. Louisiana’s coastal geography places it at the center of the animal’s range.

The marsh rice rat is a common resident of the wetlands that define the Louisiana landscape, from the Atchafalaya Basin to the coastal marshes of Terrebonne and Lafourche parishes, and throughout the interior bayous of Acadiana. Infected animals carry the virus in their urine, feces, and saliva. The virus becomes a human health hazard when it is disturbed and becomes airborne, typically during cleaning, demolition, or any activity that stirs up dried rodent waste in an enclosed or poorly ventilated space.

The marsh rice rat is not the only carrier. The LDH annual report notes that most confirmed Louisiana cases have been linked to rat or mouse-infested buildings, not direct outdoor exposure to marsh species. Common house rats and mice are the more frequent point of contact for residents.

Recent Cases and What They Tell Us

In 2022 and 2023, two Louisiana residents were diagnosed with hantavirus cardiopulmonary syndrome caused by Bayou virus. The study documenting those cases, published in February 2025 by researchers from the Louisiana Department of Health, the CDC, and Louisiana State University, produced two findings with direct implications for residents.

First, genetic sequencing of the virus from both patients showed they were separate spillover events from different rodent populations, not a connected transmission chain. The two people did not infect each other. Each contracted Bayou virus independently, from different rodents in different locations.

Second, the researchers concluded that this pattern of separate spillovers points to a probable wide distribution of Bayou hantavirus in rodents across Louisiana. The virus is not confined to a single area of the state. Human cases reflect isolated contacts with a broadly distributed rodent reservoir.

One of the two 2022-2023 patients died. The other required intensive care.

Prior to those cases, the LDH reports seven confirmed hantavirus cases in Louisiana since 2006. Four of those seven had exposure outside the state, meaning three were contracted right here. The numbers are small, but hantavirus is rare everywhere. Small case counts do not mean low risk when exposure occurs.

Who Is Most at Risk in Louisiana

The CDC identifies rodent infestation in and around the home as the primary risk factor for hantavirus exposure in the United States, and the LDH data confirm that pattern holds in Louisiana.

The highest-risk activities are those that disturb enclosed, poorly ventilated spaces where rodents have been active: cleaning out a shed, camp house, or storage building that has sat unused; opening up a camp or hunting cabin at the start of the season; moving stored materials that have been undisturbed for months; or renovating older structures with evidence of long-term rodent activity.

Outdoor exposures do occur, particularly for people who work or spend time in or near wetland environments. But the majority of Louisiana cases have come from indoor exposure to infested structures, not from direct contact with marsh wildlife.

How to Protect Yourself

Because there is no licensed vaccine for hantavirus and no specific antiviral treatment, avoiding exposure is the only reliable defense. The CDC’s guidance on rodent control and safe cleanup is the authoritative resource, and several steps apply directly to Louisiana conditions.

Keeping rodents out:

Seal gaps and holes in the exterior of your home, including around pipes, utility lines, and the foundation. Mice can enter through openings as small as a quarter inch. Steel wool, wire mesh, and cement are effective sealants. Store food, including pet food, in rodent-proof containers. Keep garbage in cans with tight-fitting lids. Clear brush, woodpiles, and debris away from the foundation of the house, as these provide nesting habitat. Move woodpiles and compost bins away from the structure.

Before entering an unused space with rodent activity:

Open doors and windows and allow the space to ventilate for at least 30 minutes before entering. Do not begin cleaning immediately upon arrival. Wear rubber or nitrile gloves. For spaces with heavy infestation, respiratory protection is appropriate, at minimum an N95 respirator.

Cleaning up rodent droppings and nesting materials:

Do not sweep or vacuum droppings or nesting materials. Dry sweeping or vacuuming can aerosolize the virus and put it directly into the air you breathe. Instead, spray droppings, nesting materials, and any dead rodents thoroughly with a 10% bleach solution (one part bleach, nine parts water) or an EPA-registered disinfectant. Let it soak for at least five minutes. Then wipe up the material with paper towels and dispose of it in a sealed garbage bag. Mop or sponge the area with additional disinfectant. Wash gloved hands before removing gloves, then wash hands with soap and water after.

For structures with extensive, long-term infestation, contact a licensed pest control professional before attempting any cleanup. Some situations warrant professional remediation.

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Symptoms and When to Call a Doctor

Early symptoms of hantavirus pulmonary syndrome resemble the flu: fever, fatigue, and muscle aches, particularly in the thighs, hips, back, and shoulders. Nausea, vomiting, and diarrhea can also occur. These symptoms typically appear one to eight weeks after exposure.

The symptom that requires immediate medical attention is respiratory distress. Four to ten days after the initial symptoms, some patients develop a cough, shortness of breath, and a tightening sensation in the chest as fluid accumulates in the lungs. That progression can be rapid.

If you have had contact with rodents or rodent-infested spaces and develop any of these symptoms, contact a physician immediately and tell them about the potential exposure. Do not wait for the respiratory phase to seek care. According to the CDC, patients with suspected HPS can deteriorate rapidly and delayed care reduces the chance of survival. Testing done in the first 72 hours of symptoms may return a negative result before the virus is detectable; repeat testing after 72 hours of symptom onset is often required to confirm the diagnosis.

The Louisiana Department of Health is the primary contact for reporting potential exposures and for guidance on clinical testing.

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