What Is Tularemia?

Tularemia is an infectious disease caused by the bacterium, Francisella tularensis (F. tularensis). This illness is characterized by painful swelling of the lymph nodes and can lead to various other symptoms that affect the lungs, eyes, throat, and intestines, depending on the site of bacterial infection within the body.

Tularemia is categorized as a zoonotic disease, indicating that it can be transmitted between animals and humans. It is often referred to informally as "rabbit fever" or "deer fly fever" because people contract tularemia through exposure to deer flies and ticks that carry F. tularensis infections. The infection occurs through contact with animals, primarily rabbits, hares, and rodents, or by consuming contaminated food and water sources carrying the bacterium.¹

Types of tularemia

Tularemia presents itself in several distinct forms, each dependent on the mode of F. tularensis infection and the location of the associated symptoms. The various types of tularemia include:

1. Ulceroglandular Tularemia: this is the most common form and is typically contracted through tick bites or contact with infected animals. It primarily affects the skin and lymph nodes.
2. Glandular Tularemia: this type also affects the lymph nodes predominantly and is typically acquired through tick bites or direct contact with infected animals
3. Oculoglandular Tularemia: this form occurs when contaminated water or bodily fluids come into contact with the eye. It manifests symptoms in and around the affected eye, usually not affecting both eyes simultaneously.
4. Oropharyngeal Tularemia: this type is contracted through the consumption of contaminated food or water or by touching the mouth with unwashed hands. It leads to a sore throat and occasionally gastrointestinal symptoms.
5. Pneumonic Tularemia: pneumonic tularemia is the most severe form, resembling pneumonia in symptoms. It can be acquired through inhalation of F. tularensis or when the bacterium spreads to the lungs from another part of the body.
6. Typhoidal Tularemia: typhoidal tularemia results in high fever and affects multiple body systems. It can be contracted through the same means as other forms of tularemia¹

Symptoms and causes

Symptoms

Tularemia symptoms generally begin to manifest between 2 to 5 days after infection, although the incubation period can range from as short as one day to as long as three weeks. Natural infection with the bacterium F. tularensis can result in various symptoms:

1. Ulcers: these are quite common and typically develop at the site of an infected insect bite or, in some cases, on the surface of the eye following exposure to airborne bacteria. These ulcers may be accompanied by swollen lymph nodes, general discomfort, and fevers
2. Sore throat, pharyngitis, or tonsillitis: these symptoms may arise after the consumption of contaminated food or water
3. Acute flu-like illness: this presentation is less frequent but can occur, often accompanied by symptoms such as diarrhoea and vomiting. It typically follows the inhalation or ingestion of the bacteria.
4. Pneumonia and blood poisoning: these are the most severe and least common natural forms of the disease. They are more likely to occur following the deliberate airborne release of the bacteria. Symptoms may include a sudden onset of high fever, chills, muscle aches, dry cough, and weakness.

In terms of physical signs, around 20% of patients may develop a blotchy, macular, maculopapular, or pustular rash. Additionally, patients often present with fever and may have tender hepatosplenomegaly (enlarged liver and spleen). The specific physical findings can vary depending on the clinical form of the disease presentation.²  

Causes

As mentioned previously, tularemia is caused by the bacterium Francisella tularensis (F. tularensis). This bacterium resides in animals, which serve as reservoirs for the disease. Commonly, these animals include rabbits, hares, rodents, and cats. Additionally, ticks and other biting insects mayact as carriers for F. tularensis.

There are two distinct types of F. tularensis: type A and type B. Type A is associated with more severe forms of the illness and is primarily found in the United States. Type B, on the other hand, leads to milder symptoms and is also prevalent in North America and most other regions across the world. Type B F. tularensis typically leads to a milder form of tularemia, and in some cases, individuals infected with this type may remain asymptomatic (showing no symptoms). In contrast, Type A F. tularensis is associated with more severe illness, with the potential to cause death in a small percentage of untreated patients, typically ranging from 5-7%.¹

Diagnosis and tests

To diagnose tularemia, healthcare providers follow a comprehensive process that involves physical examination, symptom assessment, and laboratory testing of various body fluids and tissues. The specific tests and assessments conducted to diagnose tularemia include:

1. Physical Examination: The healthcare provider will perform a physical examination to assess  the patient’s overall condition and look for any physical signs, such as lymph node swelling, throat or eye symptoms, and skin ulcers, bumps, or rashes
2. Blood tests: A blood sample is taken and sent to a laboratory for analysis. The lab will examine the blood for indicators of tularemia and may attempt to cultivate F. tularensis bacteria from the sample. It's worth noting that initial blood tests may appear normal because F. tularensis can have slow growth rates. Therefore, you may need to repeat blood tests after a few weeks.
3. Biopsy: If you have significant lymph node enlargement or skin ulcers, your healthcare provider may perform a tissue biopsy. That is, a sample of tissue is collected and sent to a lab for testing, aiming to detect the presence of F. tularensis or its growth.
4. Nasal or throat swab: a swab with a soft tip is used to collect mucus samples from your nose or throat. These samples are then sent to a lab to be tested for the presence of F. tularensis or its growth.
5. Pleural fluid test (thoracentesis): In cases where fluid accumulation is present around the lungs, a procedure called thoracentesis may be performed to extract a sample of this pleural fluid. The fluid sample is sent to a lab for testing, aiming to detect the presence of F. tularensis or its growth.

The combination of these assessments and tests helps healthcare providers establish a conclusive diagnosis of tularemia.¹

Management and treatment

The treatment of tularemia involves the administration of broad-spectrum antibiotics, which can be delivered through injections or oral pills, depending on the severity and type of infection. In cases with serious complications, additional treatments may be necessary.

It is crucial to initiate tularemia treatment promptly, and sometimes, healthcare providers may start antibiotic treatment before test results are available to prevent the illness from progressing.

Tularemia is indeed curable in humans, and antibiotics are effective in eliminating the bacteria responsible for the infection. The medications commonly employed in the treatment of tularemia include:

1. Streptomycin
2. Gentamicin*
3. Doxycycline
4. Azithromycin
5. Ciprofloxacin or levofloxacin

Patients should adhere to their prescribed antibiotic regimen until completion unless otherwise directed by their healthcare provider. Premature discontinuation of antibiotics may allow residual bacteria to persist in the body and potentially lead to a recurrence of the infection.

In addition to prescribed antibiotics, some symptoms of tularemia may be managed at home. Patients can inquire with their healthcare provider about the appropriateness of over-the-counter (OTC) medications or other therapies for symptom relief while under treatment.¹

FAQs

How to prevent Tularemia?

Preventing naturally occurring tularemia primarily relies on the following measures:

1. Avoiding tick bites: To reduce the risk of tick bites, wear long trousers and shirts with long sleeves, use tick repellents, and frequently inspect their bodies for any evidence of ticks. If ticks are found, they should be removed promptly, taking care not to squeeze the tick's body, as tick secretions may carry the infection.
2. Take precautions when handling wildlife: it is advisable to wear gloves as a precautionary measure when engaging in activities that involve handling dead or wild animals, such as skinning or eviscerating a rabbit carcass.
3. Thorough cooking of wild animal meats: if consuming wild animal meats, it is essential to cook them thoroughly before eating, as cooking can help eliminate any potential bacteria or pathogens.
4. Frequent and thorough hand washing: maintaining good hygiene practices, particularly frequent and thorough hand washing, can help reduce the risk of infection.
5. Post-exposure prophylaxis: in cases of potential exposure to tularemia, post-exposure prophylaxis with antibiotics such as streptomycin, gentamicin, doxycycline, or ciprofloxacin is recommended. These antibiotics should be taken for a minimum of 14 days.

It is important to note that while the development of a vaccine could be an effective means of preventing tularemia, an officially approved vaccine with both proven efficacy and safety has not yet been developed, particularly for addressing potential bioterrorism threats.

Who is more at risk of tularemia?

Individuals at higher risk for tularemia include:

1. Hunting or handling game: those who engage in hunting or handling uncooked game meat may be at elevated risk due to potential contact with infected animals.
2. Occupational exposure: people in professions such as veterinarians, animal control officers, or anyone who regularly handles animals as part of their job are at a higher risk.
3. Exposure to biting insects: being in areas where biting insects are prevalent can increase the risk of tularemia, as these insects can carry F. tularensis.
4. Weakened immune system: individuals with a weakened immune system due to conditions like HIV, cancer, or immunosuppressive medications may be more susceptible to tularemia
5. Specific occupational risks: certain professions, such as farm workers, sheep shearers, or laboratory workers who handle F. tularensis, are at risk for pneumonic tularemia
6. Geographic location: tularemia is more common in specific regions of the United States, including the south-central states, the Great Plains region, and parts of Massachusetts. Most reported cases of tularemia in the U.S. come from states like Arkansas, Oklahoma, Missouri, Nebraska, South Dakota, and Kansas.

What is the prognosis of tularemia?

The expected recovery prognosis for most individuals with tularemia is generally favourable, and they typically make a full recuperate recovery with appropriate antibiotic treatment. The duration of antibiotic treatment typically ranges from 10 to 21 days, although the time it takes to fully recover and feel completely better may vary from person to person. It's important to complete the full course of antibiotics as prescribed by your healthcare provider to ensure the infection is thoroughly eradicated.

Depending on the severity of symptoms and the timing of treatment initiation, healthcare providers may closely monitor patients during the initial days of treatment. Delayed initiation of treatment, especially if symptoms have been present for an extended period before antibiotic administration, can increase the risk of serious complications.

In some cases, individuals may experience a relapse of symptoms after initially feeling better. If a relapse occurs, it may necessitate another course of antibiotics to address the resurgence of the infection. Additionally, it's worth noting that some individuals may experience skin rashes as a symptom of tularemia, and in some cases, these rashes can result in permanent scars on the skin.¹

Summary

Tularemia is brought on by infection with the zootonic bacterium,  Francisella tularensis (F. tularensis). The most common symptom is painful swollen lymph nodes, but it can also present with others that target multiple areas of the body, such as the eyes and lungs. The different types of tularemia relate to the mode of infection and predict the associated physical signs and symptoms. These symptoms usually show a few days after infection, but there is a varying incubation period to be mindful of. Importantly, multiple diagnostic tests are used to detect the infection, and it is normally managed using broad-spectrum antibiotics in conjunction with pre-approved over-the-counter (OTC) medications or home remedies. Tularemia can affect anyone, but certain occupational or lifestyle factors may increase the risk of exposure to F. tularensis however, some precautions can be taken to protect yourself. While tularemia symptoms can persist for several weeks, most patients who receive timely and appropriate treatment tend to recover completely from the infection. Early diagnosis and treatment play a crucial role in improving the prognosis and reducing the severity of the illness.