Francisella tularensis is a gram-negative bacteria and the agent causing tularemia, also called rabbit fever. The species was originally discovered in squirrels in Tulare County in 1911, the county for which the bacterium is named. A year later it was isolated by George Walter McCoy, who classified the bacterium into four different strains: tularensis, the most virulent of the four, paleartica, novicida, and madiasiatica.
Francisella tularensis has been known to infect small mammals such as rabbits, muskrats, mice, and also humans. Interestingly however, is that no case of tularemia has appeared to be caused through human to human contact. Infection has appeared to always be caused by contact with infected animals or forms of transmission such as mosquitoes or ticks that have bitten infected animals. As such, the most common form of transmission is through skin contact, although airborne forms of the bacteria exist as well.
Direct contact with an infected host generally leads to the appearance of lesions on the skin, which is the most common characteristic of infection in humans. This condition usually becomes visible three to five days after contact. Because infection travels most frequently through biting insects, it can be difficult to determine whether or not the legion shows the presence of an infection or simply the result of a bite.
Another mode of transmission is through direct inhalation of Francisella tularensis. For example, hunters are more prone to infection that other individuals because they spend a larger amount of time around infected insects, and can also accidentally inhale airborne particles when skinning infected animals. Infection can also spread through infected water sources or undercooked meat. Tularemia has never been dangerously common in the US, although most incidences of the disease occur in North America and parts of Asia. That being said, several small outbreaks have been documented, including Washington DC, Kosovo, and Texas, although either minimal or no human fatalities were reported for these incidences.
The Center for Disease Control and Prevention, or CDC, has labeled Francisella tularensis as a Class A agent for biological warfare. It has been labeled this way for several factors: ease of aerosolizing, highly infective, highly incapacitating to individuals that become infected, and has a low mortality rate which is important when using the toxin near civilians. In addition, no vaccine is widely available to the public, although prevention is rather simple through the use of long sleeves to prevent tick bites and the use of gloves when dealing with wild game.