Histopathologic Changes in Suckling Mice Infected with the Virus of Colorado Tick Fever

Abstract

The principal and constant histopathologic changes in suckling Swiss albino mice infected with recent isolates of Colorado tick fever virus were found in the heart and brain. These changes were the same in all mice regardless of whether virus was obtained from patients'' blood or the vector tick, Dermacentor andersoni. Lesions in the heart consisted of widespread necrosis of cardiac muscle fibers, and moderate mononuclear cell infiltration of the damaged areas. Although necrosis and mild inflammatory changes often occurred throughout the brain, liquefaction necrosis of cerebellar folia was the principal intracerebral lesion. Other, less constant, lesions included mild inflammatory and degenerative changes in the spinal cord, focal necrosis of fat pads and skeletal muscle, and pericentral hepatic necrosis. Severe acute involution of the thymus, regressive changes in the retinas, and pulmonary congestion also were found in many mice. Myocardial and cerebellar lesions in this host constitute a histopathologic pattern which appears to be peculiar to Colorado tick fever virus infection and, therefore, offers some assistance in the tentative identification of the virus.