Francisella Tularensis - Subspecies

Subspecies

This species was discovered in ground squirrels in Tulare County, California in 1911; Bacterium tularense was soon isolated by George Walter McCoy of the US Plague Lab in San Francisco and reported in 1912. Four subspecies (biovars) of F. tularensis have been classified.

1. The biovar tularensis (or type A) is found predominantly in North America and is the most virulent of the four known subspecies and is associated with lethal pulmonary infections.
2. Biovar palearctica (also known as biovar holarctica or type B) is found predominantly in Europe and Asia but rarely leads to fatal disease. An attenuated live vaccine strain of subspecies palearctica has been described, though it is not yet fully licensed by the FDA as a vaccine. This biovar lacks the citrulline ureidase activity and ability to produce acid from glucose of biovar palearctica.
3. Subspecies novicida (previously classified as F. novicida) was characterized as a relatively nonvirulent strain; only two tularemia cases in North America have been attributed to novicida and these were only in severely immunocompromised individuals.
4. Biovar mediasiatica, is found primarily in central Asia; little is currently known about this subspecies or its ability to infect humans.