NBC News
Arizona health officials are warning that hantavirus, a virus transmitted to humans by rodents, is causing an increase in a potentially deadly lung syndrome. According to a recent health alert, seven cases and three deaths have been confirmed in the past six months.
Most cases of hantavirus occur in the western and southwestern United States. Most states, including California, typically report between one and four cases per year. Two people in California have been infected with hantavirus in 2024.
There is no specific treatment or vaccine to protect against infection.
Arizona has one of the highest total numbers of reported hantavirus infections in the United States, according to the Centers for Disease Control and Prevention (CDC).
Between 2016 and 2022, there have been 11 cases of hantavirus in Arizona: four in 2016, two in 2017, four in 2020 and one in 2022, according to the Arizona Department of Health Services.
“Hantavirus is a rare but important cause of severe, even fatal, respiratory infection,” said Dr. Aaron Glatt, chief of infectious diseases at Mount Sinai South Nassau Hospital on Long Island, New York.
“It is transmitted by various rodents, especially the deer mouse, and can cause a mild illness, but it causes a fatal condition in a significant percentage of people who contract the disease,” he said.
Additionally, San Diego County is reporting increased activity of hantavirus-infected rodents this year, with 17 cases of infected mice. In general, hantavirus activity can fluctuate from year to year and does not appear to be higher than usual in the United States in 2024, according to the California Department of Public Health.
Why are cases increasing in Arizona?
The CDC has reported 850 cases from 1993 to 2021, or about 30 cases per year.
Trish Lees, public information officer at Coconino County Health and Human Services, said the rise in Arizona cases may be due to changes in rodent populations, which can fluctuate seasonally and annually.
Although cases can occur at any time, they are more prevalent in the summer because of increased rodent activity as people come into contact with them more often, as they spend more time outdoors and enter enclosed spaces such as a shed or barn, Lees said.
“Climate can influence hantavirus emergence in complicated ways — for example, heavy spring rains may increase deer mouse food resources, leading to increased rodent populations — but no link has been shown between extreme heat and increased hantavirus activity,” the California Department of Public Health said.
Experts speculate that the climate crisis, such as the extreme heat waves that are sweeping the region, may be partly to blame.
Dr. Camilo Mora, a professor in the Department of Geography and Environment at the University of Hawaii at Mānoa, says people aren’t the only ones who seek shelter when it’s too hot or too wet. Other species also seek respite from bad weather, particularly pathogen-carrying mammals.
According to their previous research, more than half of infectious diseases affecting humans may be exacerbated by the climate crisis.
“Many disease-carrying species are set in motion by the climate crisis, so while it is difficult to pinpoint the role of this context in a specific case, it does have all the hallmarks of causing disease outbreaks,” he says.
Dr. Scott Roberts, associate medical director of infection prevention at Yale School of Medicine in New Haven, Connecticut, added that fluctuating environmental conditions can cause changes in animal populations, so increasing the rodent population, where hantavirus circulates, will inevitably increase the risk of human exposure.
Hot weather may also have worsened illnesses after people became infected due to dehydration or other factors, Glatt added.
According to the CDC, about 94% of hantavirus infections occur west of the Mississippi River.
Symptoms of hantavirus
Particles containing hantavirus become airborne when deer mouse urine, saliva, or feces are stirred up, causing hantavirus pulmonary syndrome (HPS).
The syndrome was first recognized in 1993, after a mysterious illness infected members of a Navajo tribe living on the border of New Mexico and Arizona, according to an earlier report. About 80 percent of those infected died at the time.
Symptoms may appear between one and eight weeks after exposure to an infected rodent.
The disease is divided into two phases.
In the early stages of the disease, people may suddenly start complaining of non-specific symptoms:
- Fever
- Fatigue
- Muscle pain, especially in the thighs, back and shoulders
- Nausea, vomiting and abdominal pain
If left untreated, the disease can worsen and infect the lungs, where it causes fluid to “leak” through blood vessels, causing fluid to fill the airways and cause shortness of breath, chest tightness and coughing, according to the American Lung Association.
Approximately 38% of people who develop lung symptoms may die from the disease.
How to prevent hantavirus
“The best way to prevent the spread of this disease is to carefully disinfect and clean rodent waste and not come into contact with them,” Glatt said.
The Wyoming Department of Health is warning that caution is needed during spring cleanup. The department has not observed any unusual activity so far this year among its residents in the state, an official confirmed.
The risk may be increased by opening or cleaning cabins, sheds, barns or storage buildings in rural areas that have been closed during the winter and where deer mice have entered, experts said.
In 2012, at least 10 people became ill and three died during a hantavirus outbreak among visitors staying overnight in tent cabins at Yosemite National Park.
When entering a place that has been closed and unoccupied for a long time, try to air out the space for 30 minutes, warns the Wyoming Department of Health.
If the space is very dirty or infested with mice, take extra precautions by wearing gloves, shoe covers, and N95 masks before cleaning.