Q fever pathophysiology

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

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Overview

Q fever is a disease caused by C.burnetii, an intracellular gram-negative proteobacterium. The disease can have a wide range of clinical presentations and affect many organ systems due to the unique virulence factors of the organism.

Pathophysiology

Transmission

The organism is transmitted through:

• Aerosoloes: Inhalation of contaminated aerosoles is the main mode of transmission.
• Ingestion of raw dairy products
• Vertical (mother to fetus) transmission has been reported
• Parentral
• Through tick bites

Pathogenesis

C. burnetii has the ability to exist in 2 forms:

Small cell form

Often described as the spore form of C. burnetii Resists the external environmental factors as heat, pressure and disinfectants for long periods.

Large cell form

The active form of the organism large cell form persists in the macrophages inside acidic vacuoles.

• Small and large cell forms are antigenically different and this plays a role in the virulence of the organism.
• The genome of C. burnetii has been analyzed in 1995. Multiple genes encoding for Na/ ion proton exchanger have been discovered and this explains the ability of the organism to survive in low PH.
• The infection has 2 phases that correlate with changes in the lipopolysaccharide of C. burnetii:
  • Phase I: characterized by smooth lipopolysaccharide capsule. Despite being less efficient in the invasion of host cells, antibodies against phase I is always isolated from acute Q fever patients.
  • Phase II: characterized by rough lipopolysaccharide capsule and antibodies against phase II have been isolated from chronic Q fever patients.

Q fever as a biological weapon

• Because of its route of infection it can be used as a biological warfare agent.
• Q-fever is category "B" agent. It is highly contagious and very stable in aerosols in a wide range of temperatures.
• Just 1-2 particles are enough to infect an individual.
• Q-fever microorganisms may survive on surfaces up to 60 days (like sporulating bacteria).
• According to WHO estimates, an amount of 50 kg of C. burnetii if spread in an area of 2 square kilometers is capable of:

• Infecting 500,000 humans
• Killing 150 individuals
• Causing acute illness in 125,000 individuals
• Causing chronic illness in 9,000 individuals

Microscopic pathology

• C. burnetii is a gram negative polymorphic intracellular organism.
• It was previously classified as a rickettsia, but now is considered a proteobacterium.

Coxiella brutenii	Immunohistochemical detection of Coxiella burnetii in resected cardiac valve of a 60-year-old man with Q fever - By Mahamat A, Edouard S, Demar M, Abboud P, Patrice J-Y, La Scola B, et al. -Public domain-, via Wikime