Francisella tularensis subsp. tularensis is a highly infectious bacterium that causes tularemia, a serious disease primarily affecting animals but can also infect humans. It is a small, gram-negative rod that can survive in various environments, including water and soil. The bacterium is often transmitted through contact with infected animals, bites from infected insects, or inhalation of contaminated aerosols. Tularemia can manifest in several forms, including ulceroglandular, glandular, and pneumonic, depending on the route of infection. Symptoms may include fever, skin ulcers, and swollen lymph nodes. Prompt diagnosis and treatment with antibiotics are essential to manage the infection effectively.