Francisella tularensis

Introduction

Untreated, tularemia has a mortality rate of 5-15%; this rate is even higher with the typhoidal form. Appropriate antibiotics lower this rate to about 1% (Medscape)

Hosts

Human and animal

Transmission / Exposure Route

Tularemia is a zoonotic disease that can be transmitted through cutaneous, ingestion and inhalation routes. There are four subtypes of F. tularensis with varying origination and virulence. Only two are clinically and epidemiologically important. F. tularensis subsp. tularensisis most virulent and comes from rabbits and ticks predominantly in North America. F. tularensis subsp. holarcitca is found in Asia and Europe and is a milder form that is responsible for waterborne outbreaks. ^[1]

Case Fatality Ratio

Untreated, tularemia has a mortality rate of 5-15%; this rate is even higher with the typhoidal form. Appropriate antibiotics lower this rate to about 1%. ^[2]

Incubation Period

Incubation period is typically 3-6 days.^[3]

Burden of Disease

The incidence of Tularemia from the 1950's has decreased from >5 to 0.5 cases per 1 million U.S. inhabitants^[4]

Duration of infectiousness and disease

Symptomology

Symptoms may vary depending on how the bacteria have entered the body. Swelling of regional lymph glands accompany most forms of infection. Ulcers form on the skin if the infection has been transmitted through a tick or deer fly bite to the skin. Eye irritation can be caused by the bacteria entering through the eye. More serious forms of infection occur when the bacteria are ingested through the mouth, either with food and water or by inhalation. Symptoms may then include cough, chest pain, sore throat, difficulty breathing, mouth ulcers, and tonsillitis.^[5]

Excretion Rates (see Exposure)

Immunity

Natural in vivo immunities include an increase in IgM, IgG, and IgA serum antibodies directed against Francisella Lipopolysaccharide which can be detected 6-10 days after symptom onset. Antibody levels peak 1-2 months after infection and persist for approximately 10 years before reducing in numbers. ^[6] No effective vaccine is currently available^[4]

Microbiology

Pathogenic species of gram-negative bacteria and the causative agent of tularemia or rabbit fever. It is a facultative intracellular bacterium

Enviromental Survival

Capable of surviving outside of a mammalian host for weeks