Rickettsia rickettsii str. Iowa

Rickettsia rickettsii is the causative agent of the Rocky Mountain spotted fever (RMSF) and is the prototype bacterium in the spotted fever group of rickettsiae. It is transmitted by hard ticks (Ixodidae). Rocky Mountain spotted fever is the most severe and most frequently reported rickettsial illness in the United States. It also occurs in Mexico and in Central and South America. The symptoms of the Rocky Mountain spotted fever may follow within one to fourteen days after the victim has been bitten. There is a high fever, with chills, muscle aches and a severe headache concentrated in the forehead area. Also, eyes may become red, muscles may feel weak and there may be body swelling. A rash also forms around the third to fifth day. RMSF affects about 800 people in the United States each year. Before anti-biotic treatment was available 20 to 30 percent of the cases were fatal. However, with the discovery of an antibiotic, the suffering and danger has decreased; it causes death in about 15 percent of its victims over age 70, and in only about two percent of infected victims under age 30. If an antibiotic is started rapidly, the mortality rate is ten percent.Rickettsia rickettsii (strain Iowa) is avirulent and defective in cell lysis. It does not induce fever in a guinea pig model of infection. A deletion truncates the rompA gene that codes for a major surface antigen. In addition R. rickettsii (strain Iowa) is defective in the processing of rOmpB, another major surface antigen. These factors most likely contribute to the avirulence of this strain. (HAMAP: RICRO)