Dr. Elias E. Manuelidis, 74, an internationally known expert on viral brain infections and brain tumors, died of a stroke Wednesday at Yale-New Haven Hospital. He was professor emeritus of neuropathology and neurology at Yale and taught there from 1951 until 1989. He continued his research until the time of his death, particularly on Creutzfeldt-Jakob disease, a degenerative disease of the nervous system. Dr. Manuelidis built a reputation on his work on Alzheimer's disease and polio virus, but most of all Creutzfeldt-Jakob, which often strikes in mid-life and is usually fatal. Among his contributions was to demonstrate viremia in the disease -- the presence of viruses in the blood, often characterized by malaise, fever and aching of the back and extremities. He verified how people can become infected with contaminated tissue transplants and thought that infection with the virus might be more common than is generally realized. Other contributions included the first long-term tissue culture of human brain tumors, in 1959, and, in 1964, the demonstration that a virus could be used selectively to kill a malignant tumor.