Q fever: the neglected biothreat agent.

Coxiella burnetii is the causative agent of Q fever, a disease with a spectrum of presentations from the mild to fatal, including chronic sequelae. Since its discovery in 1935, it has been shown to infect a wide range of hosts, including humans. A recent outbreak in Europe reminds us that this is still a significant pathogen of concern, very transmissible and with a very low infectious dose. For these reasons it has also featured regularly on various threat lists, as it may be considered by the unscrupulous for use as a bioweapon. As an intracellular pathogen, it has remained an enigmatic organism due to the inability to culture it on laboratory media. As a result, interactions with the host have been difficult to elucidate and we still have a very limited understanding of the molecular mechanisms of virulence. However, two recent developments will open up our understanding of C. burnetii: the first axenic growth medium capable of supporting cell-free growth, and the production of the first isogenic mutant. We are approaching an exciting time for expanding our knowledge of this organism in the next few years.