Arizona health officials are warning that hantavirus, a virus transmitted from rodents to humans, is causing a rise in cases of a potentially deadly pulmonary syndrome. According to a recent health alert, there have been seven confirmed cases and three deaths in the past six months.
Most cases of hantavirus are reported in the western and southwestern United States. Most states, including California, typically report one to four cases per year. Two people in California have been infected with hantavirus this year.
There is no specific treatment or vaccine to protect against infection.
According to the Centers for Disease Control and Prevention, Arizona has one of the highest total number of reported hantavirus infections in the United States.
Between 2016 and 2022, there were 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 serious and sometimes 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, particularly the deer mouse, and can cause mild illness, but it causes fatal illness in a significant percentage of people who contract the disease,” he said.
Additionally, San Diego County is reporting increased activity in hantavirus-infected rodents this year, with 17 cases of harvest mice infected with hantavirus. Overall, hantavirus activity can fluctuate from year to year and does not appear to be higher than usual in the United States this year, the California Department of Public Health said.
Why are cases increasing in Arizona?
The CDC reported 850 cases from 1993 to 2021, or about 30 cases per year.
Trish Lees, public information officer for the Coconino County Department of Health and Human Services, said the increase in cases in Arizona could be due to changes in rodent populations, which can fluctuate seasonally and annually.
Although cases can occur at any time, they are more common in the summer due to increased rodent activity and people coming into contact with them more often because they are outdoors more often and entering enclosed spaces like a shed or barn, Lees said.
“Weather can influence hantavirus outbreaks in complex ways—for example, heavy spring rains can increase food supplies for deer mice, leading to increased rodent populations—but no link has been demonstrated between extreme heat and increased hantavirus activity,” the California Department of Public Health said.
Experts believe climate change, including extreme heat waves hitting the country, may be partly to blame.
According to Dr. Camilo Mora, a professor in the Department of Geography and Environment at the University of Hawaii at Manoa, humans aren’t the only ones seeking shelter when it’s raining or very hot outside. Other species also seek refuge from the elements, particularly mammals that carry pathogens.
His previous research found that more than half of infectious diseases that affect humans may be worsened by climate change.
“Many disease-carrying species are moving due to climate change. So while it is difficult to determine the role of climate change in each specific case, it has all the attributes to cause vector-borne disease outbreaks,” he said.
Dr. Scott Roberts, associate medical director for infection prevention at Yale School of Medicine in New Haven, Conn., added that fluctuating environmental conditions can lead to 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 said.
According to the CDC, about 94% of hantavirus infections occur west of the Mississippi River.
Symptoms of Hantavirus
Particles containing hantavirus enter the air when the urine, saliva or droppings of deer mice are stirred up, causing hantavirus pulmonary syndrome (HPS).
The syndrome was first identified in 1993 after a mysterious illness infected members of a Navajo tribe that lived on the New Mexico-Arizona border, according to an earlier report. About 80% of those infected died at the time.
Symptoms may appear one to eight weeks after exposure to an infected rodent.
The disease is divided into two phases.
At the onset 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, causing fluid to “leak” into the blood vessels, causing the airways to fill and causing shortness of breath, chest tightness and coughing, according to the American Lung Association.
About 38% of people who develop lung symptoms may die from the disease.
How to prevent hantavirus
“The best way to prevent infection with this disease is to thoroughly disinfect and clean up all rodent waste and not come into contact with them,” Glatt said.
The Wyoming Department of Health is recommending caution when spring cleaning. The department has not seen any unusual activity so far this year among state residents, a public information officer confirmed.
The risk may increase when opening or cleaning cabins, sheds, barns or storage buildings in rural areas that have been closed for the winter and where deer mice have entered, experts say.
In 2012, at least 10 people were sickened and three died during a hantavirus outbreak among visitors who spent the night in tent cabins in Yosemite National Park.
When entering a closed, unoccupied space, be sure to air the space for 30 minutes, the Wyoming Department of Health warns.
If the space is very dirty or full of mice, be extra careful by wearing gloves, shoe covers, coveralls, and N95 masks before cleaning.