'Rabbit fever' cases rising in US as CDC warns of zoonotic bacterial disease

Cases of tularemia, also known as "rabbit fever," are on the rise in the U.S., according to a new report from the Centers for Disease Control and Prevention (CDC).

Caused by the bacteria Francisella tularensis, the disease commonly infects rabbits, hares and rodents. However, it is zoonotic, which means it can spread from animals to humans.

The bacteria is a "tier-1 select agent," a classification given to agents and toxins that "present the greatest risk of deliberate misuse with significant potential for mass casualties or devastating effects to the economy, critical infrastructure or public confidence, and pose a severe threat to public health and safety," per the CDC. 

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Although tularemia is relatively rare, with only 2,462 diagnoses between 2011 and 2022, cases have risen 56% compared to the prior decade (2001 to 2010), as reported in the CDC's Morbidity and Mortality Weekly Report.

"Increased reporting of probable cases might be associated with an actual increase in human infection, improved tularemia detection or both," the report states.

Daniel Ruderfer, M.D., chief of the Division of Pediatric Infectious Diseases at Hackensack Meridian K. Hovnanian Children's Hospital in New Jersey, believes that the increase in cases is mostly due to improved microbiology detection methods.

"The traditional method of confirming cases has historically been via growth in culture and antibody testing," he told Fox News Digital. 

"However, newer detection methods, such as PCR testing, are likely a major contributor to the increase in reported cases."

Humans can contract the disease through bites from deer flies or ticks, contact with infected animals, or exposure to contaminated water or aerosols, the same source stated.

Symptoms of tularemia can vary depending on the type of disease.

General symptoms include chills, headache, malaise, fatigue, anorexia, myalgia, chest discomfort, cough, severe sore throat, vomiting, diarrhea, and abdominal pain, according to Ruderfer.

"Depending on the location of the infected bit or scratch, people can develop localized lymphadenopathy (enlarged lymph nodes) and a cutaneous ulcer at the infection site," he said. 

"Other manifestations include conjuctivitis, pneumonia and potentially even bloodstream infections."

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The death rate from the disease is typically low, less than 2%, but the CDC noted that it can be as high as 24% in rare, severe cases.

Tularemia can be treated with antibiotics, but no vaccine is currently available.

"The infection is absolutely dangerous and potentially life-threatening if not treated with appropriate antibiotics," said Ruderfer.

Those most at risk include children between 5 and 9 years of age, older men, American Indian and Alaskan Native people, and those living in central U.S. states, according to the report.

The general population is not at an "obvious" risk for infection unless they come into physical contact with an infected rabbit, tick or deer fly, the expert noted. 

Those who hunt or interact routinely with rabbits should see a doctor if they develop any concerning symptoms, he advised.

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"Many factors might contribute to the higher risk for tularemia in this population, including the concentration of Native American reservations in central states and sociocultural or occupational activities that might increase contact with infected wildlife or arthropods," the CDC wrote.