Introduction 

Tularemia is an infectious disease caused by the bacteria Francisella tularensis. It is transferred through the contact of infected rabbits, rodents, tick bites and other animal bites. The risk factors for this disease are veterinarians, farmers and hunters. You can also be infected by eating uncooked/undercooked wild meat. Tularemia can affect various regions of the body which include lymph nodes, eyes, skin, lungs and throat. As it is a bacterial infection it can be treated with antibiotics.

What is tularemia?

Tularemia is a zoonotic disease which means it spreads by contact between animals and humans. It is caused by highly infectious bacteria Francisella F.tularensis which is a gram-negative bacteria. Other names for this disease are Francis’ disease, rabbit fever, and deer-fly fever. It is a rare disease and people living in the rural areas have a high risk of being infected by this disease as the people have more contact with animals than the urban areas.

A study says that about 200 cases of tularemia are reported each year in the United States,¹ mostly caused by the bites of the infected ticks, rabbits etc, in some cases, the person can also be infected by inhaling the infected airborne particles. The signs and symptoms depend on the route of the infections, ranging from asymptomatic to severe.

What does tularemia look like?

Tularemia causes the lymph nodes in the body to become swollen and inflamed, and they can be seen as scary red bumps on the affected area or the whole body.

Causes of tularemia

Tularemia occurs when a person is exposed to the infectious bacteria through various means, including:

• Insect bites
• Direct contact with infected animals
• Ingestion of contaminated food or water
• Inhalation of contaminated aerosols
• Laboratory exposure
• Animal bites

Bacteria responsible: F.tularensis

F.tularensis is the bacterium that causes this rare and highly infectious disease. It is highly infectious due to the fact that a small number of bacteria is enough to cause the disease and harm the health of the animals and humans. This makes it more infectious than the other bacteria, which need a large number of bacteria to show the signs and symptoms of the disease. Once inside the body, F.tularensis invades the cells and replicate frequently resulting in the spreading of the disease.

F.tularensis is considered as a Category A Bioterrorism agent by Centers for Disease Control and Prevention (CDC)² because it is easily spreadable by aerosols which causes a serious threat to human lives, resulting in high mortality rates and panic. The inhalation of the bacterium can cause pneumonic tularemia, which is the most severe form of the disease.

Pathophysiology of tularemia

The bacteria enters the host cells and infects the macrophages. Macrophages are white blood cells which provide us immunity by safeguarding our body against the microbes. Now, F.tularensis bacteria infects these macrophages and further replicates inside of them, which leads to lysis of the cell release of the bacteria to more regions in the body.

Transmission from animals

Rabbits, ticks and other wild animals such as rodents are the animals affected by this bacteria. The animals get affected by Tularemia by consuming contaminated food/uncooked food. 

They can also inhale the bacteria, which affects the lungs and causes pneumonia. The bacteria invade the cells of the animals and replicate quickly, weakening the immunity of the animals. The animal's symptoms don't show until it's been 10 days, after being infected they may show symptoms such as fever, chills, distress and tiredness. 

Now, when these infected animals come in contact with humans, they transmit the disease to them. It can be through direct contact with the animals, inhalation of the air particles contaminated with the bacteria. Human-to-human transmission of the disease is not reported.³

Modes of transmission

Tick and insect bites (ticks, deer flies)

It is the most common source of transmission of the disease, so if any tick or insect infected with the bacteria bites you, then you are at high risk of developing the disease.

Direct contact with infected animals (handling, skinning)

People who handle, skin, or butcher infected animals, particularly wild rabbits, hares, and rodents, are at risk. The bacteria can enter the body through small cuts on the skin or through mucous membranes in the eyes, nose, or mouth. 

Other people at risk of developing this disease are Hunters, trappers, veterinarians, and laboratory workers due to increased exposure to potentially infected animals.

Inhalation of contaminated dust or aerosols

Inhalation of dust or aerosols containing F.tularensis can occur during activities such as farming, or construction work in areas where the bacteria is present. This can lead to pneumonic tularemia, the most severe form, characterized by fever, cough, and chest pain.

Contaminated water or food sources

F.tularensis can survive in water for prolonged time. Drinking contaminated water can lead to symptoms such as sore throat, mouth ulcers, and swelling of the lymph glands (oropharyngeal tularemia).

It can also be present in uncooked meat or unclean vegetables. Upon the ingestion, it can upset the stomach and cause symptoms such as Diarrhea, abdominal pain and vomiting. 

Sign and symptoms

The symptoms for the disease occur abruptly, after an incubation period of 3-15 days⁴ in humans. The symptoms include fever, chill, malaise and fatigue. The signs and symptoms are further differentiated according to the type of the Tularemia.

Types of tularemia⁵

Ulceroglandular tularemia

It is the most common form caused by skin contact with infected animals. The person infected will present with skin lesions, swollen lymph nodes and fever. The lymph nodes get tender, inflamed and painful causing skin ulcers.

Glandular tularemia

It is the second most common form and it causes enlarged swollen lymph nodes, without an ulcer formation.

Oculoglandular tularemia

There is an infection of the conjunctiva of eyes due to rubbing of the eyes with unwashed hands (e.g., rubbing the eye after handling infected animals). It usually affects one eye and you may see symptoms such as pain, swelling, red and runny eyes. It may also cause photophobia i.e. fear of light. The glands in the jaw, neck or around the ear are also swollen.

Oropharyngeal tularemia

It is caused by direct ingestion of contaminated food or water. The mouth and throat are affected and it shows symptoms such as fever, sore throat, tonsillitis and gastrointestinal symptoms such as stomach pain, diarrhoea and vomiting.

Pneumonic tularemia

This is caused by inhaling bacteria, leading to respiratory issues (the most serious form). You may feel symptoms such as fever, cough, malaise, difficulty in breathing and chest pain.

Diagnostic tests

Diagnosis is based on the symptoms and risk factors. Some tests performed are as follows 

Serology test

It is a diagnostic test which checks the blood and serum to look for antibodies against the bacteria. If the antibodies are present in the bodies then it means you are infected by the F.tularensis bacteria.

Culture media

This is an alternative to the serology test, basically the sample of the infected region is taken and it is cultured in a suitable medium to look for the growth of the bacteria. For F.tularensis bacteria bacteria growth is more seen in McCoy and sulfhydryl medium. 

Treatment

Tularemia can be treated with antibiotics since it is a bacterial infection. The drugs used for the treatment of Tularemia are:

Streptomycin

It is the drug of choice for the treatment for most forms of tularemia. It is administered intramuscularly and is very effective in treating the infection.

Gentamicin

Gentamicin is an effective alternative option to streptomycin. It is specifically useful for patients with mild to moderate disease. Gentamicin can be administered Intramuscularly or intravenously.

Doxycycline and ciprofloxacin

Oral antibiotics are effective for milder cases and can be used in outpatient settings. They are also suitable for patients who cannot tolerate aminoglycosides.

The duration period is 14 days for the full recovery of the Tularemia. Your doctor will inform you about the importance of strictly following the course of 2 weeks for complete removal of the bacteria from the body, ensuring fast recovery.

Importance of early diagnosis and treatment of tularemia

Early diagnosis and treatment of tularemia are important to prevent serious complications such as respiratory failure, sepsis, and multiorgan failure The disease can progress rapidly, and specific antibiotics such as streptomycin, doxycycline, and ciprofloxacin are most effective.

Timely treatment also reduces the risk of chronic health issues, reduces the chances of infectious disease, and reduces the overall healthcare burden through the need for referral the length of hospitalization.

Summary

Tularemia is a bacterial infection caused by the F.tularensis bacteria. Another name for this disease is rabbit fever. This disease is transmitted by the infected animals to the humans via direct contact, inhaling the airborne particles or by eating the uncooked/undercooked meat. The bacteria attack the white blood cells of the host, decreasing the immunity of the person. The people at risk factors are farmers, vets and butchers. Tularemia signs and symptoms vary depending on the route of the infection but mostly all of them cause fever, tiredness and fatigue. The most common form of the tularemia is ulceroglandular. The first-line drug for the treatment is streptomycin because it is the most effective against the bacteria. Early diagnosis and treatment prevent any serious issues such as respiratory failure and reduce the disease from further progression.