Francisella tularensis and tularemia: Morphology and Identification, Pathogenesis and Clinical Findings, Diagnostic Laboratory Tests, Treatment, Prevention and Control.

Question 1

Francisella tularensis: morphology and identification

Answer 1

Francisella tularensis is a very small, pleomorphic, Gram-negative coccobacillus. It is nonmotile, non–spore-forming, and encapsulated. It is an obligate aerobe and fastidious, requiring cysteine-enriched media such as buffered charcoal yeast extract (BCYE) or chocolate agar. It stains poorly with Gram stain and is a facultative intracellular pathogen.

Question 2

Francisella tularensis: pathogenesis

Answer 2

F. tularensis enters the body through skin, mucous membranes, or lungs. It is phagocytosed by macrophages but escapes phagosomes and replicates intracellularly. It spreads to lymph nodes, liver, spleen, lungs, and bone marrow. It causes granulomatous inflammation and necrosis. Very low infectious dose (as few as 10 organisms) makes it highly virulent and a potential bioterror agent.

Question 3

Francisella tularensis: clinical findings

Answer 3

Tularemia presents in several forms based on route of entry: 1) Ulceroglandular (most common) – skin ulcer with regional lymphadenopathy; 2) Glandular – lymphadenopathy without ulcer; 3) Oculoglandular – conjunctivitis with lymphadenopathy; 4) Oropharyngeal – sore throat, mouth ulcers, GI symptoms from ingestion; 5) Pneumonic – cough, chest pain, high mortality; 6) Typhoidal – systemic illness without clear local signs. Fever, chills, and malaise are common in all forms.

Question 4

Francisella tularensis: diagnostic laboratory tests

Answer 4

Diagnosis is primarily clinical and supported by serology (antibody detection), which shows a fourfold rise or high titer. Culture is difficult and hazardous (requires BSL-3 facilities) but can be performed on cysteine-rich media. PCR and direct fluorescent antibody (DFA) tests are also available. Lymphocytosis and elevated liver enzymes may be seen in blood tests.

Question 5

Francisella tularensis: treatment

Answer 5

The drug of choice is streptomycin. Gentamicin is an effective alternative. Doxycycline or ciprofloxacin can be used for mild to moderate disease or as post-exposure prophylaxis. Early treatment shortens illness duration. Relapses may occur with inadequate treatment.

Question 6

Francisella tularensis: prevention and control

Answer 6

Avoidance of exposure to wild animals (especially rabbits), ticks, and deer flies is key. Use protective clothing and insect repellents in endemic areas. Handle animal carcasses with care. No licensed vaccine is available to the general public, but a live attenuated vaccine exists for laboratory workers. F. tularensis is a potential bioterrorism agent (Category A) and must be reported to public health authorities.