THE ENHANCING EFFECT OF MURINE HEPATITIS VIRUS ON THE CEREBRAL ACTIVITY OF PLEUROPNEUMONIA-LIKE ORGANISMS IN MICE

Nelson, John B.

Shortly after the isolation of MHV(C) from Balb C mice, in 1955, it was found that Swiss weanlings were equally susceptible and because of their availability they were subsequently used in activity tests (1) . Princeton mice were consistently resistant. Intraperitoneal injection in Swiss mice was generally followed by focal or diffuse necrosis of the liver but was not attended by nervous manifestations. On intracerebral injection the virus produced significant changes in the brain, with some destruction of nerve cells. Lymphocytic infiltration was commonly observed in brain sections but polymorphonuclear leukocytes were absent. Lesions produced in the liver, following carriage of the virus from the brain, were generally focal in character. The death rate was variable. In one series of passages, 12 of 25 mice died between the 3rd and the 5th day after injection. Survival after the 3rd day was irregularly attended by paralysis of the hind legs. The most common sign was a rigid backward extension of one or both limbs. The affected leg was functionless and was dragged by the mouse in moving. This type of paralysis was observed in 9 of the 25 mice. At autopsy on the 5th or 6th day, 5 of them were erect and active while 4 were prone and unable to move. A tendency to roll sideways, if lightly prodded, was observed in one of the latter mice. All of the cranially injected animals showed weight losses of 1 to 3 gin.