Vitamin D Intake and Susceptibility of Mice to Experimental Swine Influenza Virus Infection.

Considerable interest has been manifested in recent years in the influence of nutrition on experimental infection. Reviews on the subject have been written by Aycock and Lutman,( 1 ) Schneider,( 2 ) and more recently by Clark et al.( 3 ) More specifically related to the results presented in this paper is the work of Sprunt( 4 ) who demonstrated that mice, maintained on low protein diets, showed, after injection with methionine, an increased susceptibility to swine influenza virus infection. Similarly, Midzuno( 5 ) was able to produce influenza in rats by maintaining them on diets deficient in vitamin D. He also carried out similar experiments with avitaminotic D mice. In this paper results are presented which indicate that mice fed diets low in vitamin D are more susceptible to experimental swine influenza virus infection than are mice that receive vitamin D. These findings confirm those reported by Midzuno.( 5 ) Materials and methods. Experimental animals. The mice were obtained by 3 successive matings of 75 females and 35 males of second generation stock derived from Bittner's ZBC strain( 6 ) with a commercial strain of Swiss mice. The breeding colony was maintained on Purina Fox Checkers and water. To assure uniformity in the ages of the test mice, all breedings for each replicate of the experiment were carried out within a period of 7 days. Mice were weaned at 21 days, and then placed on the experimental diets for 28 days. Thus, at the time of inoculation with swine influenza virus, the mice were at least 49 days old and not more than 56 days old. Experimental diets. The basal diet was prepared by hand mixing all the ingredients listed in Table I, except the brewers' yeast, which was added later as the vehicle for vitamin D.