Rats carry several dangerous viruses, including hantaviruses (most notably Seoul virus), lymphocytic choriomeningitis virus (LCMV), and, in parts of West Africa, Lassa fever virus. These viruses typically spread to humans not through bites but through contact with rat urine, droppings, and saliva, especially when dried waste becomes airborne dust.
How Rat Viruses Spread to Humans
The most common route of infection is inhaling virus particles that have become airborne. When rat urine, droppings, or nesting materials dry out and are later disturbed (by sweeping, moving boxes, or entering a shed), tiny contaminated particles float into the air. Breathing these in is the primary way people get infected. Direct contact with rat waste or contaminated surfaces, and less commonly a bite or scratch, can also transmit viruses.
This is why cleaning up rat-infested spaces is itself a risk. The CDC recommends never sweeping or vacuuming rodent droppings, which kicks particles into the air. Instead, soak the area first with a disinfectant or a bleach solution of 1 part bleach to 9 parts water. Wear rubber or plastic gloves for light cleanups. For heavy infestations, full protective gear is recommended, including coveralls, goggles, and a respirator with a HEPA filter.
Seoul Virus: The Global Hantavirus in Rats
Seoul virus is the most widespread rat-borne hantavirus in the world, carried by both brown rats and black rats, the two species most commonly found near humans. It was first isolated from a wharf rat in Philadelphia in 1984 and has since been identified on every inhabited continent. Unlike other hantaviruses that are tied to specific wild rodent species in limited regions, Seoul virus travels wherever rats go.
What makes Seoul virus particularly notable is its presence in pet rats. A distinct genetic lineage of the virus circulates in domesticated rat populations, likely from a single introduction that then spread internationally through the pet trade. The exposure risk from pet rats may actually exceed that from wild rodents. A 2014 study in the United Kingdom found that 34.1% of pet rat owners had antibodies against Seoul virus, compared to just 3.3% of healthy blood donors and 1.7% of farmers.
Seoul virus causes hemorrhagic fever with renal syndrome (HFRS), a disease that primarily affects the kidneys. The illness typically moves through five stages. It starts with a febrile phase lasting 3 to 7 days, with facial flushing, bloodshot eyes, and the early signs of kidney injury. This can progress to a hypotensive stage (dropping blood pressure lasting hours to two days), then an oliguric stage where the kidneys produce very little urine for 3 to 7 days. If the patient recovers through these dangerous phases, a diuretic stage follows with excessive urination for two to three weeks, and then a slow convalescent period that can stretch 3 to 6 months with lingering fatigue and muscle aches.
The hypotensive and oliguric stages carry the highest risk of death, accounting for roughly one-third and one-half of HFRS fatalities respectively. Bleeding complications, including bruising, blood in urine, and in severe cases intracranial hemorrhage, can occur. That said, the course of HFRS is usually self-limiting. Most patients fully recover, and kidney function typically returns to normal.
Hantavirus Pulmonary Syndrome
While Seoul virus targets the kidneys, hantaviruses found in the Americas (such as Sin Nombre virus) cause a different illness: hantavirus pulmonary syndrome, or HPS, which attacks the lungs. These viruses are carried primarily by deer mice rather than common rats, but the distinction matters because the diseases look very different. HPS begins with fever, fatigue, and muscle aches, then rapidly progresses to severe breathing difficulty as the lungs fill with fluid.
HPS is rare but serious. Since surveillance began in 1993, 864 total cases of hantavirus disease had been reported in the United States through the end of 2022, with 834 of those being the pulmonary form. The case fatality rate is high, making prevention through rodent control especially important in rural areas of the western United States where deer mice are common.
Lymphocytic Choriomeningitis Virus (LCMV)
LCMV is carried by house mice and, to a lesser extent, by rats. In healthy adults, infection typically causes a flu-like illness or a form of viral meningitis that resolves on its own. Many infections produce no symptoms at all.
The real danger is during pregnancy. LCMV can cross the placenta and infect a developing fetus, with devastating consequences. Infection raises the risk of miscarriage, fetal death, and severe birth defects affecting the brain and eyes. In one documented case, a woman who experienced a brief flu-like illness during her 16th week of pregnancy was later found to be carrying a fetus with severe microcephaly, abnormal brain folds, and calcifications throughout the brain tissue. Because LCMV symptoms in the mother are so mild and nonspecific, infections during pregnancy can easily go unrecognized until fetal damage is already done. Pregnant women should avoid contact with rodents and their waste.
Lassa Fever Virus
Lassa fever is caused by a virus carried by the multimammate rat, a species found throughout Sub-Saharan Africa. Currently, only populations in West Africa, specifically in Sierra Leone, Liberia, Guinea, and Nigeria, are known to carry the virus. People in neighboring countries are also at risk because the rat’s range extends across the region.
Lassa fever ranges from mild to fatal. Most infections cause mild symptoms or none at all, but severe cases can involve bleeding, organ failure, and death. For travelers or people living in endemic areas, the primary prevention strategy is the same as with other rat-borne viruses: keeping rodents out of living spaces and avoiding contact with their waste.
Reducing Your Risk
The common thread across all rat-borne viruses is that prevention comes down to limiting contact with rats and their waste. Seal gaps in your home’s foundation and walls, since rats can squeeze through openings as small as half an inch. Store food in sealed containers, and don’t leave pet food out overnight. Keep outdoor areas clear of debris that provides nesting material.
If you find evidence of rats in your home, the cleanup itself requires caution. Ventilate the space for at least 30 minutes before entering. Spray droppings and nesting material with your bleach solution (1.5 cups of household bleach per gallon of water) and let it soak for at least five minutes before wiping up with paper towels. Double-bag everything and dispose of it in a sealed trash container. Wash your hands thoroughly afterward, even if you wore gloves the entire time.
Pet rat owners face a unique concern with Seoul virus. Infected rats often show no visible signs of illness, so there’s no way to tell by looking whether a pet rat carries the virus. If you own pet rats and develop unexplained fever, muscle aches, or signs of kidney problems, mention your rat exposure to your doctor, since Seoul virus is underdiagnosed partly because clinicians don’t think to test for it.