A new study found that an extremely infectious pneumonia-like disease in humans slips through the immune system’s usual defense mechanisms. Mark Wewers The bacterium at fault, Francisella tularensis, causes the disease tularemia. Also known as rabbit fever, tularemia is fatal in less than 1 percent of treated cases and in about 5 percent of untreated cases. It is a rare disease with only about 300 cases per year occurring in the United States .But the disease can make many people very ill very fast, said Mark Wewers, the study’s lead author and an assistant director of the Davis Heart and Lung Research Institute at Ohio State University . He and his colleagues report their findings in this week’s online edition of the Proceedings of the National Academy of Sciences.