Introduction   

Tularemia is a zoonotic disease (a disease that spreads from animals to humans or vice-a-versa, but humans cannot transmit the disease to other humans) caused by a gram negative bacteria called ‘Francisella tularensis’. The bacteria is transmitted mainly through direct animal contact or through a carrier, e.g. a tick. Tularemia impacts children, adults and elderly but it is common in young males aged 5 to 9 years and the elderly over 75 years of age.⁵

Tularemia is known by many different names such as “Rabbit fever”,”Deer-fly fever”,”Francis disease” and “Ohara’s disease”. 

It is a highly infectious disease that can cause serious illness even with a small number of bacteria and can enter the body through a variety of routes. 

The risk of Tularemia is highest in¹

• Farmers
• Landscapers
• Those who regularly work with animals like sheep, rabbits
• Those who routinely handle meat (butchers, meat cutters, etc.)
• Veterinarians

It is important to understand the spread of the disease, its symptoms, treatments, how it impacts different age groups and those with comorbidities.

Subspecies of Tularemia

Tularemia bacteria have multiple subspecies that determine their prevalence in different geographical areas. These subspecies are divided into 2 categories:

Type A: Tularensis

The most virulent subspecies, found in North America, it infects humans through rabbit ticks.

It is considered a biological weapon by the US Centres for Disease Control and Prevention (CDC).²

Type B: Holarctica

This subspecies is found in the Northern Hemisphere, including Europe and Asia. It spreads in humans through direct contact, inhalation, ingestion or insect bites from infected rodents and hares.

Mediasciatica

Novicida

Prevalence and statistics of the disease

Cases of the disease have been reported all over the USA except for Hawaii.³ Most of the cases are reported from May through September. It is more prevalent in males as compared to females.³

Types of Tularemia and its symptoms

Tularemia is classified into different types based on its route of entry into the human body and the area of the body that it affects the most. Tularemia is a febrile disease with an incubation period that can range from one day to three weeks, but symptoms begin to present themselves between 2 to 5 days.

Tularemia presents itself in the following types:

Diagnosis

Tularemia is diagnosed by the clinician using clinical evaluation supported by confirmatory diagnostic tests.

The diagnostic tests include:

• Blood tests: serological tests to check presence of antibodies to Tularemia bacteria in the blood sample (ideally taken after 14 days after the onset of illness)
• Clinical specimens:
• Ulcer scrapings
• Nasal or throat swabs
• Conjunctival swabs
• Lymph node aspirates
• Pleural fluid
• Confirmatory tests:
• Polymerase Chain Reaction (PCR)
• Immunohistochemistry (IHC)
• Cultures

Treatment and Prognosis

Depending on the severity of the disease and the type of Tularemia infection, broad spectrum antibiotics are prescribed either through oral or injection route. The infection is extremely virulent which necessitates prompt treatment and management of symptoms. Antibiotics used for treatment of Tularemia are:

• Streptomycin
• Gentamicin
• Doxycycline 
• Azithromycin
• Ciprofloxacin or Levofloxacin

The prognosis of Tularemia with treatment is excellent while untreated cases result in 10-50% mortality.¹

Tularemia impact on different age groups

In general, tularemia impacts very young and the elderly as compared to adults because of their developing or debilitating immunities respectively. 

Impact of Tularemia on children

Generally, children have a stronger immune response to infections than the elderly but may still be vulnerable due to their developing immune systems.

Studies have shown that Tularemia affects children differently than adults. 

Infants and young children (up to 5 years)

• Infants and young children are more susceptible and at a higher risk of suffering from severe forms of Tularemia, causing pneumonia, meningitis or septicemia which can be life threatening if not treated promptly
• They may present with fever, irritability along with other symptoms

Children and adolescents (up to 17 years)

• The ulceroglandular and glandular types of Tularemia are commonly seen in this age group
• The symptoms include fever, weakness, skin ulcers and swollen painful or painless lymph nodes near the entry point of infection.

The presence of an entry point lesion with anatomically corresponding lymph node swelling must indicate a Tularemia infection and must be treated with Ciprofloxacin or Doxycycline as first line of treatment in children.⁵

A detailed examination, including examination of the scalp for entry point lesions and diagnosis of Tularemia must be considered for children with severe swollen lymph nodes and infection of the tonsils (tonsillitis) who show no response to beta lactam antibiotics like penicillin and cephalosporins.⁴

It is important to detect and start the treatment early as tularemia in children requires longer duration of antibiotic treatment along with surgery to remove the infected area.⁶

Impact of Tularemia on adults

Adults generally have a stronger immune system to fight the infection. The ulceroglandular or glandular types are common, but inhalational exposure can cause pneumonic type of Tularemia.

The symptoms depend on the type and the entry point of the infection in the body. Prompt treatment can result in faster recovery from the infection. Individuals with comorbidities like diabetes, hypertension, heart or kidney disease are at a risk of longer recovery times than healthy individuals.

Chances of adults working in high risk occupations are more likely to catch the infection.

Impact of Tularemia on the elderly

Declining immune function in the elderly makes them vulnerable to infections and increases their risk of complications (sepsis, pneumonia, organ failure) from Tularemia, particularly the pneumonic or typhoidal types. Similarly, existing comorbidities further weaken the immune system and a delayed diagnosis of the infection can do severe damage if not treated promptly. 

Another challenge with antibiotic treatment in elderly is the drug interactions and contraindications of certain drugs, which may affect the treatment efficiency. The dosage has to be adjusted or limited to avoid any side effects due to declining liver and kidney function. This prolongs the treatment further and requires close monitoring.

Impact of Tularemia on the immunocompromised

Immunocompromised patients, suffering from cancer, HIV/AIDS, organ transplant patients or those receiving immunosuppressive drug therapies are at an increased risk of suffering from complications if infected by Tularemia bacteria. Their weakened immune systems make it difficult to mount a response to the infection leading to an increased likelihood of severe forms of the infection which can progress rapidly and cause septic shock or multi-organ failure. These individuals are also at a higher risk of relapse or secondary infection and prolonged treatment. Careful and supervised management is crucial to treat the infection in such individuals, though the overall prognosis remains poor as compared to healthy individuals.

Preventive measures such as avoiding exposure to vectors or infected animals are important in such high risk populations.

Summary

Tularemia, an infection caused by bacterium ‘Francisella tularensis”’ affects individuals across all age groups, including the elderly, but its impact varies significantly. In infants and young children, tularemia can present in severe forms like pneumonia or septicemia and can cause devastating outcomes, if not treated promptly. Adolescents and adults with  healthy immune systems often present with localised infections and less severe symptoms, however, those in high risk occupations or immunocompromised conditions face significant risks. The elderly, are particularly vulnerable as age related or comorbidity related immune decline increases the chances of severe outcomes, leading to respiratory distress or multi-organ failure.

The prognosis of tularemia improves with early detection and antibiotic therapy. Delayed symptom presentation, comorbidities like diabetes and weak immune status influence the severity as well as recovery of the disease.

The only way to combat tularemia is by:

• Preventive measures like avoiding or minimising exposure are the most important until immunity against the infection is developed
• Vaccination: several clinical trials for vaccine against tularemia are ongoing but none have been licensed for use as of today