Distemper virus infection in ferrets: an animal model of measles-induced immunosuppression

Distemper virus is very similar antigenically to measles virus, and the disease produced in ferrets by distemper is a systemic illness quite similar to measles infection in humans. Using an attenuated strain of distemper virus, we produced a mild systemic illness in ferrets and were able to study the effects of the viral infection on cell-mediated immunity (CMI). Beginning on day 5 after viral inoculation and continuing to day 30, infected ferrets showed a marked lymphopenia, with a reduction in total numbers of all lymphocyte subpopulations studied. Transformation of circulating lymphocytes to the mitogens phytohemagglutinin, concanavalin A, and pokeweed mitogen was suppressed on day 5, reached a nadir by days 8 to 11, and returned toward normal by days 23 to 30 after viral inoculation. Production of macrophage migration inhibitory factor by splenic macrophages was diminished during distemper infection. In contrast to marked suppression of these in vitro assays for CMI, delayed hypersensitivity skin test responses were only slightly diminished in animals infected with distemper virus. This model should prove useful in exploring the mechanisms of measles induced immunosuppression.