Colorado Tick Fever and Dengue

Six human beings were inoculated with dengue and developed typical disease. Two of these were reinoculated and proved immune. The remaining four were later inoculated with Colorado tick fever. Three developed typical disease. The fourth, who remained well, has previously lived in an endemic area (Colorado). One patient was inoculated with Colorado tick fever first and later with dengue. He developed both diseases. Colorado tick fever and dengue do not give a cross-immunity. Hamsters can be infected with Colorado tick fever but not with dengue. Colorado tick fever and dengue appear to be distinct disease entities.