Susceptibility of BL6 nude (congenitally athymic) mice to Japanese encephalitis virus by the peripheral route.

Studies on the susceptibility of adult BL6 nude (congenitally athymic, nu/nu) mice, their euthymic littermates (+/nu) and Swiss mice to Japanese encephalitis (JE) virus inoculated subcutaneously were carried out. The mice were observed over a period of 60 days p.i. for sickness and/or death, which was noticed only in nu/nu mice. However, the onset and the duration of sickness varied and no definite pattern was observed. Thirty four of 53 nu/nu, 28 of 42 +/nu and 30 of 52 Swiss mice bled during the first 5 days p.i. exhibited viraemia. Interestingly, only nu/nu mice had secondary viraemia during the period of sickness. The cause of sickness and death in nu/nu mice was confirmed by recovering the virus from the blood, the brain and other organs. Antibodies were detected in the sera of +/nu and Swiss mice from the 10th day p.i. onwards but not in nu/nu mice. These findings indicate the important role of functional T cells both in induction of active immunity and protection against JE virus infection in mice.