Infection in Mice Following Nasal Instillation of Louping-Ill Virus

Abstract

Regular transmission to mice of a fatal infection following intranasal instillation of louping-ill virus, apparently not accomplished until now, 1 , 2 , 3 , 4 , 5 has been effected by the employment of brother-sister inbred strains of mice. 6

White-face and black-and-tan mice, brother to sister inbred, for at least 10 generations and maintained on a standard diet and uniform routine in a special breeding room, have reacted in a consistent and characteristic manner to the virus obtained from T. M. Rivers. This virus, the Moredun Strain from Mackie, has proved infective for mice and monkeys when injected intracerebrally and gives rise to the characteristic signs and histopathology of louping-ill. 2 , 3 , 4 , 5

Intranasal transmission has been carried out as follows: Brains from 2 to 4 mice dead of the experimental infection induced by intranasal or intracerebral injection are removed aseptically, cultured, weighed, ground in a sterile mortar, diluted in normal saline, and again cultured for contaminants. Duplicate batches of 20 mice each are given 0.02 cc. of the diluted virus into the nares through a 0.25 cc. tuberculin syringe and blunt needle. Care is taken not to touch or injure the nasal tissues. The mice are then placed in individual jars and observed over a 4 week period. Animals found dead are autopsied and cultured for bacterial growth. Passage in series from the brains of mice dying from intranasal instillation to the nasal passages of normal mice has been continued in parallel series successfully and uniformly 8 times.

When white-face mice are used dilutions of virus from 1 to 2 to 1 to 20 result in an incubation period of 6 to 7 days, followed by rapid and progressive development of hyperesthesia, tremors, incoordination, partial paralysis, especially of the hind limbs, prostration, and finally death between the eighth and tenth days in practically every case.