Mississippians were urged to protect themselves against mosquito bites after confirmation that an 11-year-old boy died of rare eastern equine encephalitis, or sleeping sickness. Dr. Ted Tsai of the Centers for Disease Control office in Ft. Collins, Colo., said it was the first reported death from the disease this year, and the state Health Department said it was the first case of the disease in Mississippi in at least a decade. Tsai said the fatality rate is about 30%. The boy, who lived in a heavily wooded area of southern Mississippi, died Aug. 6, said Lisa Ruble, Health Department spokeswoman. Entomologist Jerome Goddard said the disease is carried by birds and is occasionally transmitted to horses and humans by mosquitoes. Cases occur along the Eastern Seaboard and Gulf Coast as well as in Canada and Central and South America.