Suckling Mouse Cataract Agent (SMCA) in Mice

Abstract

Summary SMCA virus induces cataracts in a high percentage of infected suckling mice. Maximal SMCA-induced cataract rates were obtained only when virus doses of 104.0 ELD50 or greater were inoculated intracerebrally into suckling mice 4 days of age or younger. Virus inoculated by the intravenous or intraperitoneal routes did not produce cataracts. The SMCA-induced cataract rate was mouse strain-dependent. Cataract rates, based on eye examination at age 30 days, varied from 85% in strain C57B1/6Ha mice to 3% in strain A mice. After 30 days, rates decreased in most mouse strains, but in strain A mice the cataract rate gradually increased to a rate of 44% at 1 year (late cataract strain). Comparative virus assays were performed of the brains, liver-spleen tissues and eyes of SMCA-inoculated strain CFW(A) (30-day cataract rate 46%) and strain A (30-day cataract rate 3%) mice. In each mouse strain virus reached peak titers in all tissues studied in 7 to 15 days. Virus titers then slowly decreased, disappearing from liver-spleen tissues and most eyes by 60 days, but persisting indefinitely (up to 827 days) in the brain. Eye infection rates were similar (88% in A mice, 91% in CFW(A) mice) in both strains of mice. However, in the late cataract strain A mice, virus clearing from eyes and viscera occurred earlier, and peak titers of virus in eyes were lower than in CFW(A) mice.