Lack of Immunity to Latent Virus

Abstract

The apparent failure to encounter immune mice in the spontaneous mouse infections described by Dochez, et al., 1 and us 2 , 3 suggested this attempt to produce evidence of immunity experimentally. It is of particular interest because the host-virus relationship seemed to be latent until provoked experimentally. The virus then grew highly virulent, killing all mice that became sick. None of the surviving mice appeared to be immune to the latent virus.

Approximately 400 mice obtained at different times from a Missouri breeder were observed for varying periods of time up to 14 months. These stock mice appeared to be well although they were known to carry the virus. None of these mice died spontaneously with pneumonitis.

Mice were anesthetized with ether and inoculated intranasally with 1:20 suspension of infected lung emulsion in saline. Lungs of sick mice were cultured on blood agar plates and 30% ascitic fluid agar, aerobically and anaerobically. Occasional colonies appeared from lungs of moribund animals but no organisms grew consistently enough to have etiological significance. Pleuropneumonia-like organisms⁴, ⁵ were sought particularly since these have confused work with viruses in mice.

Groups of mice were inoculated by various routes in an attempt to immunize them. The survivors were reinoculated intranasally with virus 30 days after the initial attempts in order to test for immunity. The results are seen in Table I.

During one period of observation about 50% of the stock mice became ill and died with the disease after intranasal inoculation of sterile physiological saline. Animals that did not die after such treatment were found, nevertheless, to be susceptible to the disease by inoculation with virus. At other times saline seldom affected the mice. They were all susceptible to the disease, however, when inoculated with virus.