Rabbit Fever Outbreak: CDC Reports Alarming Surge in Human Cases Over the Last Decade

Surge in 'Rabbit Fever' Cases: CDC Report Links Rising Tularemia Incidence to Multiple Risk Factors

Tularemia, a bacterial infection more commonly known as "rabbit fever," has seen a startling rise in cases across the United States over the past decade. According to a recent report from the U.S. Centers for Disease Control and Prevention (CDC), the disease caused by the bacterium Francisella tularensis is on the upswing. Once considered relatively rare, tularemia now presents a growing concern for public health, particularly due to its varied transmission methods and its potential for severe outcomes if not treated promptly.

Tularemia is not a new disease, but its surge in human cases and the evolving landscape of how it is contracted have brought it back into the spotlight. Historically, F. tularensis has been transmitted through direct contact with infected animals, such as rabbits, hares, and rodents, or via bites from infected ticks or deer flies. However, more alarming routes of transmission have surfaced in recent years, prompting concern from public health experts.

What is Tularemia and How Does It Spread?

Tularemia is a zoonotic disease, meaning it is primarily found in animals, but can be transmitted to humans. The primary vector for the disease is Francisella tularensis, a highly infectious bacterium capable of surviving in the environment for long periods. While F. tularensis is notorious for causing widespread outbreaks in wildlife populations, it has the potential to infect humans in various ways, including:

1. Direct Contact with Infected Animals: The most common route for human infection is handling or skinning infected rabbits, hares, and rodents. These animals are particularly susceptible to the bacteria.
2. Vector-Borne Transmission: Ticks and deer flies, which feed on the blood of infected animals, can transfer the bacteria to humans during their bite. This route is more common in rural and forested areas where ticks are abundant.
3. Aerosolization from Infected Animal Nests: Perhaps the most unexpected route is when the bacteria becomes airborne. This can occur when people mow lawns or disturb animal nests that contain the bacteria, causing it to become aerosolized. This route of transmission was first observed in Massachusetts in 2000, and subsequent cases in Colorado have been linked to similar incidents, underscoring the unpredictable nature of the disease.
4. Consumption of Contaminated Water or Meat: Though rare, tularemia can also be contracted by drinking contaminated water or eating undercooked meat from infected animals.

The varied transmission routes complicate efforts to control and diagnose tularemia, making it a disease of growing concern for both individuals and public health authorities. As the CDC report highlights, the increasing number of cases over the past decade may be linked to environmental and social changes that increase the risk of exposure.

A Decade of Rising Tularemia Cases

According to the CDC’s report, there were 2,462 confirmed cases of tularemia between 2011 and 2022 across 47 U.S. states, marking a significant uptick compared to the previous decade. While this is still a relatively low incidence when compared to other infectious diseases like Salmonella (which affects millions of Americans annually), the 56% increase in reported cases from 2001-2010 to 2011-2022 is significant enough to warrant attention.

One possible factor contributing to the rise in tularemia cases is improved diagnostic practices. In 2017, the CDC began including "probable" cases—those where F. tularensis was detected via polymerase chain reaction (PCR) but not cultured—alongside confirmed cases. This change in reporting methodology has likely inflated the numbers to some extent, but it also reflects a heightened awareness of the disease and more advanced methods of detection.

Nevertheless, it seems that both actual infection rates and reporting accuracy are contributing to the surge in tularemia cases. The risk of contracting tularemia remains highest among individuals living in rural areas, particularly in regions where wildlife interactions are more common. For instance, people who work in agriculture or outdoor fields, such as hunters, landscapers, and farmers, are at a higher risk of coming into contact with infected animals or arthropods.

Why Has Tularemia Become a Public Health Concern?

While tularemia itself is relatively rare, it poses a serious health threat due to its potential to cause severe illness or even death without prompt treatment. The case fatality rate (CFR) for tularemia is typically under 2%, but this rate can be much higher depending on how the disease manifests and the infecting strain of F. tularensis. Some forms of tularemia, especially those involving pulmonary or septicemic symptoms, can lead to organ failure and death if untreated.

The bacteria can cause a variety of symptoms, depending on how the infection is contracted. In many cases, tularemia presents with flu-like symptoms, such as fever, chills, headache, and fatigue. However, it can also lead to more severe forms, including:

• Ulceroglandular Tularemia: The most common form, typically marked by skin ulcers at the site of infection and swollen lymph nodes.
• Pneumonic Tularemia: This form affects the lungs and is the most dangerous. If untreated, it can progress rapidly and lead to respiratory failure.
• Oculoglandular Tularemia: Affects the eyes, causing symptoms such as conjunctivitis, eye pain, and light sensitivity.
• Septicemic Tularemia: This severe form occurs when the bacteria spreads through the bloodstream and can lead to septic shock.

Given the disease’s potential to mimic other common infections, tularemia is often misdiagnosed in its early stages, further complicating treatment. Early diagnosis and antibiotic treatment are crucial for preventing complications, but timely recognition can be a challenge due to the variety of symptoms and the rarity of the disease.

Tularemia in At-Risk Populations

Certain populations appear to be more vulnerable to tularemia than others. The CDC’s report indicates that Indigenous populations, specifically American Indian and Alaska Native individuals, experience tularemia incidence rates approximately five times higher than the general population. Factors contributing to this disparity may include increased interaction with wildlife, as well as socio-economic and environmental factors.

Children aged 5 to 9 years and elderly men aged 65 to 84 are also at higher risk of contracting tularemia, according to the CDC data. Children may be more likely to interact with infected animals or play outdoors in environments where the bacteria are present, while older adults may have compromised immune systems that increase their susceptibility to the disease.

Preventing and Treating Tularemia

While tularemia is dangerous, it is also preventable and treatable. Key steps in preventing infection include:

• Avoiding Contact with Infected Wildlife: People who live in or visit rural areas should avoid handling sick or dead animals, especially rodents and rabbits.
• Using Insect Repellents: Wearing insect repellent and protective clothing while working outdoors can reduce the risk of tick and deer fly bites.
• Proper Hygiene: Anyone working in outdoor settings should wash their hands thoroughly and take precautions when mowing lawns or disturbing wildlife habitats.
• Antibiotics: Tularemia is highly treatable with antibiotics, particularly aminoglycosides like streptomycin or gentamicin. Early treatment can reduce the severity of the disease and prevent complications.
• Awareness and Early Diagnosis: Healthcare professionals should be aware of tularemia’s varied symptoms and routes of transmission, ensuring prompt diagnosis and treatment for at-risk individuals.

Conclusion

Tularemia may be rare, but its recent rise in cases demands attention. With the increasing recognition of environmental and socio-economic factors that elevate risk, it is more important than ever to remain vigilant about this potentially deadly disease. As scientists and public health officials continue to track the rise in cases, it is vital that individuals who live in at-risk areas take preventive measures to avoid infection. Early diagnosis and timely antibiotic treatment remain the best defense against this potentially lethal illness.