Cases of a bacterial infection called “rabbit fever” have been increasing during the past decade.

Cases of tularemia increased by 56% during the 2010s compared to the previous decade, researchers report in the CDC’s Morbidity and Mortality Weekly Report.

Half of all the nearly 2,500 reported cases between 2011 and 2022 came from four states: Arkansas, Missouri, Kansas and Oklahoma. However, cases have been reported in 47 states.

“The case fatality rate of tularemia is typically less than 2% but can be as high as 24%,” the research team led by CDC epidemiologist Kiersten Kugeler noted.

The disease is caused by the bacterium Francisella tularensis, “an organism that has been designated a tier-1 select agent based on its potential for misuse as a bioweapon,” the researchers wrote.

People can become infected by tick or deer fly bites, drinking water contaminated with the bacteria, or coming into contact with infected animals like rabbits or rodents, the CDC says.

Tularemia is treatable with antibiotics, but can develop into pneumonia if not addressed, researchers said.

Symptoms can include skin ulcers, eye infections, sore throat, cough, difficulty breathing, and swollen lymph glands, depending how the bacteria passed into a person’s body.

American Indian/Alaskan Native people are particularly at risk, with a tularemia infection rate about five times that among whites, researchers said.

Incidence was highest among children 5 to 9 years old, as well as senior men 65 and older.

Researchers noted that the findings might reflect an actual increase in human infections, or improved detection of new cases thanks to better lab tests.

People can protect themselves against tularemia by using insect repellant and wearing long pants, long sleeves and long socks to ward off ticks and deer flies, the CDC says.

They also should avoid sick animals, not mow over dead animals, and wear gloves when handling wild animals, the CDC said.