U. S. Department of Health, Education, and Welfare, Public Health Service, National Institutes of Health, National Institute of Allergy and Infectious Diseases, Rocky Mountain Laboratory, Hamilton, Montana 59840
Previous studies have indicated that Colorado tick fever (CTF) virus persists in erythrocytes of man and experimental animals for long periods. In this study, blood samples were obtained from nine patients at various intervals during and after clinical illness with CTF. Virus was isolated from erythrocytes of some patients as early as 1 day and as late as 120 days after onset of symptoms. Similar studies performed on experimentally infected Swiss mice and laboratory rats demonstrated that CTF virus persisted in their red blood cells for 60 and 50 days after inoculation, respectively. A single treatment with trypsin proved more efficient and rapid than multiple saline washes for removing neutralizing antibody from erythrocytes to allow the detection of CTF virus and viral antigens during any stage of illness or convalescence.