Experimental infection of herpesvirus cuniculi (HCV or Virus III) was studied as a model of latent infection of herpes group virus.
The growth of HCV in rabbit kidney (RK) cell cultures was rather slow when the cells were infected at a multiplicity of approximately 10. Infective virus appeared 30 hours after infection, and a maximum titer of 10
6 TCID
50/0.2ml reached on the 4th day. The infectivity titer of cellassociated virus was 2 log TCID
50 higher than that of fluid virus.
When HCV was inoculated intracutaneously or intravenously into a rabbit, it began to be detected from peripheral leukocytes on the 7th day after infection. It was isolated constantly from leukocytes over a period of at least 14 months. Concurrently, neutralizing and complement-fixing antibodies were demonstrated in the serum.
To detect infective virus, leukocytes were cultivated with RK cells. The number of leukocytes needed for positive virus isolation ranged from 800 to 100, 000, depending on the species of animals and/or the time of bleeding. No virus could be recovered from fresh leukocytes which had been disrupted by freezing and thawing before inoculated onto RK cells. It was recovered, however, when RK cells were inoculated with leukocytes which had been incubated
in vitro at 37°C for two days prior to the occurrence of disruption by freezing and thawing. These results suggest that the virus may have existed in an inactive from in fresh leukocytes, that it may have been converted in to an infective form in these leukocytes when cultivated
in vitro, and that it may have multiplied most efficiently in RK cells.
Virus was also recovered from leukocytes obtained from various organs, such as brain, lung, spleen, kidney, liver, and uterus, of rabbits which were infected with the virus 4, 6 or 14 months before and cultivated with RK cells.
In order to demonstrate that a rabbit was infected with HCV, it was a most sensitive method to isolate the virus from peripheral leukocytes cultivated with RK cells. The demonstration of neutralizing and/or complement-fixing antibodies was also useful for the same purpose. Serological surveillance of 101 rabbits obtained in the Tokyo area failed to show the production of any specific antibody against HCV.
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