Overview

Infectious diseases are a cause of concern for us worldwide. While some may be as simple as a common cold, some can be more severe and require immediate treatment. In this article, we will discuss an illness known as tularaemia, its basics, and how it compares to other infections like the plague or Lyme disease.

So, let us start with tularaemia. It is a highly infectious disease of zoonotic origin.¹ It is caused by a bacteria known as Francisella tularensis.¹ This infection is important to keep in mind as it has varying degrees of symptoms where the symptoms change based on the route of infection.¹ Tularaemia is highly infectious and can be acquired through inhalation, direct contact with the organism through cuts and wounds, ingestion, or through a tick bite, fly vector, or small animals (e.g., rabbits).¹ Tularaemia has other names associated with it, such as rabbit fever, deer fly fever, Phavant Valley plague, or Ohara’s fever.²

This bacteria is divided into different subspecies – type A (tularensis), B (holarctica), mediaasiatica, and novicida.² Type A is associated with terrestrial beings, while type B is more linked to aquatic terrains.² This bacteria is found in different areas of the world, mostly the northern hemisphere, and affects different animals; however, type A is found to be more virulent for humans than type B.²

Once infected, tularaemia can lead to multiple presentations–for example, it can lead to ulceroglandular, oculoglandular, oropharyngeal, or respiratory diseases, as well as digestive problems and typhoid illness.¹

How Does Tularaemia Compare to Other Infections?

Now that we have discussed tularaemia, we can move on to other bacterial infections and point out their differences to this infection, which can help in the diagnosis and treatment of each properly. So, let us now discuss plague and Lyme disease below.

Plague is another infection caused by bacteria.³ This bacterium is known as Yersinia pestis and has previously caused a deadly epidemic.³ This disease is known to be transmitted by fleas but also through eating contaminated food or inhaling the bacteria in the air.⁴ Once infected, the bacteria is capable of causing bubonic plague or pneumonic and septicaemic plagues.⁴ Like tularaemia, the plague is considered a zoonotic disease that is carried by rodents globally.⁴ The plague was first reported in Egypt in 541, where it later varied on to northern Europe and England and later further spread to Asia.⁴ This disease is quite rapid, and symptoms emerge very quickly after infection, making treatment essential within 24-36 hours as this can result in death within a few days if not administered.⁵

Another illness to discuss is Lyme disease. What does it mean? It is, like the other two illnesses mentioned, a zoonotic disease that is transmitted via a tick vector.⁶ Similarly to the mentioned diseases, it is also a bacterial infection due to the bacteria Borrelia burgdorferi (mostly in the U.S.) and other species of this bacteria in Europe/Asia (e.g., Borrelia afzelii or Borrelia garinii).⁷

Lyme disease can be separated into 3 stages: early, disseminated, and late stage.⁷ Sometimes, Lyme disease is referred to as Lyme borreliosis and can start as mild symptoms but can lead to serious complications if left untreated.⁷

Transmission

Tularaemia

Transmission of tularaemia is through multiple pathways; for example, it can be through eating contaminated food or through touching contaminated animals and their products.¹ It is not likely to spread from human to human, but it is worth noting that it can be spread via bites of insects or mosquitoes, which play a major role as the main insect vector.¹ This bacteria is immune to extreme temperatures (hot or cold) and can continue to live even in animal cadavers; hence, the inhalation of this bacteria from the cadaver can be possible.¹

This bacteria is highly infectious, and some people tend to be more at risk than others, for example: veterinarians or lab workers that can come in contact with the bacteria, farmers or people who work with animals, and butchers or people that handle meat.¹

Plague

Plague can be a life-threatening infection if not treated promptly; hence, it is important to understand its transmission. Yersinia pestis is generally found in the domestic black rats and brown sewer rats, while the oriental rat flea is the most common vector.⁸ Once this flea gets infected from the rats, it then transmits the bacteria to humans through bites.⁸ However, this is not the only way of acquiring the plague, as it can be ingested, inhaled, and transmitted through physical contact, especially if there are open cuts and wounds on the skin.⁸ Human-to-human transmission has also been seen. ⁸

Lyme Disease

As mentioned previously, Lyme disease is transmitted through ticks, mainly Ixodes tick species being the biggest vector.⁷ Usually, these infections happen at higher rates during late spring, summer, or early autumn.⁷ Additionally, the tick requires to be attached to the human for more than 15 hours for the infection to occur.⁷

Pathogenesis

Tularaemia

When infection with Francisella tularensis occurs, multiple cells get affected, and they can be immune cells or other types of cells.¹ This infection can lead to necrosis and micro-abscess formation.¹ Additionally, the bacteria can lower the host’s immune response, making it capable of avoiding elimination by our immunity.¹

The infection can occur through multiple routes, and if the initial infection location was close to the lymph nodes, then the residing macrophages are seen to transport the infection to other sites of the body in the early stages.¹ The incubation period will take 2 to 9 days, and some people may be asymptomatic.¹ However, most people end up getting an acute septic reaction that is then followed by death.¹

If the infection is inhaled, then sometimes this bacteria is mistaken for tuberculosis due to the formation of granuloma, which causes the confusion.¹

Plague

Plague is transmitted from rodents to fleas that then end up transmitting it to humans.⁸ When fleas get infected, they end up having a blocked gastrointestinal tract, which then leads them to feed more.⁸ During this, the fleas will regurgitate the bacteria in each bite into the human body causing infection.⁸ Similarly to tularaemia, the bacteria will go to the lymph nodes while avoiding the immune system, and the residing macrophages will carry the infection to the rest of the body.⁸

Around 80 to 95% of Yersinia pestis are related to the lymph nodes and lead to the bubonic plague (also known as the black death).⁸ If the infection goes to the blood, then it is referred to as septicaemic plague, and if it reaches the lungs, then it is known as pneumonic plague.⁸

Lyme Disease

The bacteria for Lyme disease reside within the midgut of the tick.⁷ Once the tick feeds and gets blood, this stimulates the bacteria to grow and start expressing proteins that allow it to move from the midgut to the salivary glands of the tick and closer to the mouth.⁷ Since this process requires time, ticks need to be attached to the host (humans) for at least 15 hours or more before infection can occur.⁷

Once in the body, the bacteria has mechanisms to avoid the immune system, although at times it can be caught and cleared out by our immunity.⁷ However, the bacteria can persist and eventually develop a symptomatic illness.⁷

Symptoms

Tularaemia

Symptoms for tularaemia include:^9,10

• Fever
• Headache
• Fatigue
• Inflamed lymph nodes
• Skin ulcer
• Sore throat
• Diarrhoea
• Pneumonia 

Plague

There are 3 primary forms of the plague and their symptoms:^8,11

• Bubonic: this form includes swollen and painful lymph nodes, referred to as bubo. Along with fever, body aches and chills
• Septicaemic: once the bacteria reach the blood, it can lead to septicaemic plague along with low blood pressure and shock
• Pneumonic: bubonic plague can spread and reach the lungs, leading to pneumonic plague. This is the most virulent and severe form of the plague. In this form, infected individuals can infect others through respiratory droplets and require immediate attention to treat the illness. This is because the incubation period is as short as 24 hours; hence, if not treated promptly, the results can be fatal

Lyme Disease

Signs and symptoms associated with Lyme disease include:¹²

• Early-stage symptoms such as muscle pain, fatigue, fever, headaches and a characteristic rash known as erythema migrans rash
• Later signs that appear days to months after a tick bite include:
  • facial palsy
  • arthritis
  • heart palpitations
  • nerve pain
  • inflammation in the brain and spinal cord
  • numbness in the hands or feet
  • stiff neck and more rashes in other areas of the body

Treatment

Tularaemia

Currently, there is no optimal antibiotic to treat tularaemia; however, the usual treatment given is an intravenous injection of gentamicin for 7–14 days.¹ Other drugs like ciprofloxacin can be used in mild cases.¹

Plague

Treatment of the plague is done with antibiotics such as gentamicin or streptomycin for 7 to 10 days.⁸ Currently, 17 vaccines are in production for further protection.⁸

Lyme Disease

Similarly to the other two diseases, Lyme disease is treated with antibiotics; for the early stages, supportive care and doxycycline are used for treatment, while more later and severe stages can be treated with intravenous injection for a duration of 14 days.⁷

Summary

Infections can be tricky to identify and treat if the root cause is not identified. In this article, we talked about tularaemia, the plague, and lyme disease. Tularaemia is known as rabbit fever and can lead to serious infections. It is spread through different animals and routes, such as handling meat. The plague, on the other hand, is transmitted to humans through infected fleas (from rodents) or even from one person to another and can lead to high mortality in a very short time. Meanwhile, lyme disease is spread through tick vectors and can progress to severe illness if not treated appropriately. Hence, all these infections can have detrimental results on our health, and it is important for us to see the signs and get the help needed for each case quickly.