Septicemic plague is a severe form of the plague caused by the bacterium Yersinia pestis. It occurs when the bacteria enter the bloodstream, leading to systemic infection. Symptoms can include fever, chills, rapid heartbeat, and abdominal pain. If untreated, it can progress rapidly and may be fatal. This type of plague can develop from untreated bubonic plague or can occur on its own. It is highly contagious and can spread through direct contact with infected tissues or fluids. Early diagnosis and treatment with antibiotics are crucial for improving survival rates in affected individuals.