Introduction 

Tularemia, also known as ‘rabbit fever’ or ‘deer fly fever’, is a rare but potentially severe disease caused by the bacterium Francisella tularensis. It does not occur naturally in humans but is contracted from animals such as rabbits, hares, rodents, sheep, birds and arthropods, such as ticks, through various modes of transmission. House pets, like dogs and cats, can contract tularemia too. Understanding the risk factors for contracting the disease is important, particularly for individuals with frequent exposure to animals and the environment where the bacterium may be present. 

Who is at higher risk of contracting tularemia?

Tularemia can affect anyone who comes in contact with the carrier of the bacteria, but certain groups of people are more prone to it, based on their occupation, hobbies and proximity to the environment or animals that might harbour these bacteria. Early identification of high-risk groups can lead to timely intervention, diagnosis and appropriate treatment. Below are the primary vulnerable groups of people: 

Hunters and trappers

Individuals who hunt, trap or handle carcasses of wild animals, particularly rabbits, hares, and rodents, are at a higher risk of contracting tularemia. They are exposed to animal tissue and fluids, which harbour these bacteria. For example, during skinning or butchering, there is direct skin contact, which leads to infections, particularly through cuts or abrasions on the skin. Additionally, consumption of raw or undercooked meat from infected animals also poses significant risks for gastrointestinal tularemia. 

Veterinarians and wildlife workers

Veterinarians, wildlife rehabilitation workers, and other animal care professionals frequently come into contact with sick or dead animals. Proper use of personal protective equipment (PPE) is necessary in preventing transmission while treating animals, handling carcasses, or cleaning contaminated environments. 

Agricultural workers, landscapers and farmers

People working in agriculture, landscaping, and farming often operate in environments where they are exposed to the bacterium. Tularemia can be contracted by inhaling dust contaminated by animal faeces or by being bitten by an infected insect. These workers may unknowingly come in contact with contaminated hay, soil, or vegetation. Inhalation of airborne particles is a major concern for farmers and landscapers as it can lead to pneumonic tularemia, a particularly severe form of the disease. 

Outdoor enthusiasts (Hikers, gardeners, and campers): 

People who spend a considerable amount of time in the wilderness or in rural environments are also at risk. Hikers, campers, and gardeners might encounter ticks, flies, or mosquitoes that carry Francisella tularensis. In areas with known outbreaks, these individuals should be extra protective, using insect repellents and wearing appropriate clothing to minimise the risk of insect bites.

Laboratory workers

Researchers and laboratory personnel who handle Francisella tularensis bacteria for study purposes are also at risk of contracting tularemia, especially if the lab protocols aren’t strictly followed. Laboratory-acquired tularemia can occur through accidental exposure to the bacterium during specimen handling, culturing, or aerosol inhalation. This makes it essential for the laboratory workers to follow safety measures, including the use of containment equipment, PPE, and proper disinfection practices.

Transmission methods

Tularemia can be transmitted in different ways. The most common transmission methods include: 

Direct animal contact

Touching or handling infected animals during hunting, trapping, skinning, or butchering activities is one of the primary routes of transmission. It particularly occurs during hunting or skinning infected animals. 

Insect bites

Ticks, deer flies, and mosquitoes act as vectors for tularemia. A single bite from an infected tick can transmit the bacteria, posing a threat to individuals who spend time outdoors, especially in rural areas, which are more prone to tularemia infections.

Aerosol exposure

Inhalation of dust or aerosols containing Francisella tularensis is another mode of transmission. This is particularly concerning for farmers, landscapers, and laboratory workers who may come into contact with contaminated soil, plant material, or research samples. Although rare, tularemia acquired this way tends to result in pneumonic tularemia, which can lead to severe respiratory symptoms.

Contaminated food and water

Tularemia can be contracted by consuming contaminated food or water. In some cases, water sources may become contaminated with the bacterium through animal waste or carcasses. Ingesting undercooked meat from infected animals can also lead to the gastrointestinal form of tularemia.

Types of tularemia and symptoms 

The type of tularemia one develops depends on the mode of transmission, which influences the types of symptoms and the severity of the disease. Symptoms usually start showing within 3-to-5 days of being infected, but it can take up to two weeks as well. There are different types of Tularemia that have different symptoms associated. 

Ulceroglandular tularemia

The most common form, ulceroglandular tularemia, presents with cutaneous ulcerations and marked lymphadenopathy. Its symptoms include an ulcer on the skin caused by the bite from an infected animal or insect, swollen lymph glands, fever with chills, severe headaches, and fatigue.

Oculoglandular tularemia

This type of tularemia presents with preauricular lymphadenopathy and conjunctivitis. It particularly affects the eyes and its symptoms include red eyes, sensitivity towards light, and intense pain, swelling, or discharge in the eye. It can also lead to ulcers inside the eyelids and tender lymph glands around the ear, neck, and jaw. 

Oropharyngeal tularemia

Oropharyngeal Tularemia presents with pharyngitis, stomatitis, and cervical lymphadenopathy. It affects the mouth, throat, and digestive system. It is caused by consuming undercooked meat from an infected animal or drinking water that’s contaminated. Its symptoms include throat pain, vomiting, diarrhoea, swollen tonsils or lymph nodes in the neck, ulcers in the mouth, and fever.

Pneumonic tularemia 

This is a respiratory disease that presents as pneumonia or pleurisy. It can cause symptoms that are often associated with pneumonia, including trouble with breathing, pain in the chest, and a dry cough.

Typhoidal tularemia 

A rare but very serious form of the disease, it can lead to an enlarged spleen or liver, diarrhoea, vomiting, fatigue, and fever.

Prevention strategies 

Reducing exposure to Francisella tularensis is important in preventing tularemia. Here are several ways to reduce exposure to the bacterium:

Use insect repellent

When spending time outdoors, particularly in areas known for ticks, flies, or mosquitoes, use insect repellents containing DEET, picaridin, IR3535, oil or lemon eucalyptus, para-menthane-diol, or 2-undecanone to reduce the risk of bites.

Wear protective clothing

Cover exposed skin by wearing long sleeves, long pants, and gloves, especially when handling wild animals or working in rural areas where the bacteria may be present. Use of masks during mowing may also reduce the risk of inhaling the bacterium. 

Handle animals with care

Hunters and trappers should wear gloves when handling animals and ensure that any game meat is thoroughly cooked before consumption. Also, avoid touching or mowing over dead or sick animals. 

Practice laboratory safety

Laboratory workers must follow strict biosafety protocols, including wearing protective gear, using proper containment equipment, and handling bacterial cultures with care.

Avoid contaminated water

Drink only treated or purified water in areas where tularemia is known to occur, and avoid swimming in or consuming water from sources that may be contaminated with animal waste.

Diagnosis and treatment 

Tularemia is diagnosed through a thorough clinical evaluation that isolates the bacteria from the blood, through serologic tests that measure the body’s immune system response against the bacterium. 

The disease can be treated with the use of antibiotics prescribed by the healthcare provider. Streptomycin or gentamicin are highly effective if started at an early stage. Doxycycline and ciprofloxacin may also be prescribed in milder cases. Untreated tularemia can be fatal, particularly in its pneumonic form, so prompt medical intervention is essential. 

Summary

Tularemia, though rare, poses a significant health risk to individuals who come into contact with infected animals or environments where the bacterium Francisella tularensis thrives. Identifying those at higher risk, such as hunters, agricultural workers, and outdoor enthusiasts, is essential for targeted prevention. While the disease manifests in various clinical forms, prompt diagnosis and treatment with antibiotics can effectively reduce complications. By employing protective measures, such as using insect repellents, wearing protective clothing, and handling animals safely, individuals can minimize their chances of contracting tularemia and ensure better health outcomes.

FAQs

Q: Is tularemia contagious from person to person?

A: No, tularemia is not contagious among humans. It is usually contracted through direct contact with infected animals, insect bites, or contaminated environments.

Q: Which animals are commonly associated with tularemia?

A: Rabbits, rodents, and hares are the most common carriers of tularemia, but the disease can also infect other animals like beavers, squirrels, and birds.

Q: How can I protect myself when spending time outdoors?

A: Use insect repellent, wear clothes that cover your entire body, avoid drinking untreated water, and avoid handling dead animals without protection.

Q: Can tularemia recur after initial infection? 

A: While individuals who recover from tularemia typically develop immunity, it is possible, though rare, to contract the disease more than once.