Gary L. Gitnick

Chronic rubella virus infection in the ferret (Mustela putorius fero) puppy.

Summary The inoculation of newborn ferrets with rubella virus by various routes resulted in chronic infection. Specific complement fixing antibody and neutralizing antibody persisted for at least one year after inoculation. Of 36 puppies inoculated by the IC route, 3 showed corneal cloudiness with microblepharon at 6 weeks post-infection. The IC inoculated puppies had the highest titer of virus in most of the organs examined; these animals also showed longer virus shedding, higher CF and neutralizing antibodies. There was no death or evidence of illness which could be attributable to the inoculation of rubella virus by any route. These findings are similar in many respects to those observed in congenital rubella in human infants. The suckling ferret provides a useful model for the study of the prevention and pathogenesis of rubella.

Rubella Virus Complement-Fixing Antigen Sedimentable and Non-sedimentable Antigenic Components

Summary Ether treatment of rubella virus “cell pack” antigen resulted in the production of specific sedimentable and non-sedi-mentable (“soluble”) complement-fixing preparations which were serologically indistinguishable when tested with convalescent human sera. The sedimentable antigen was found in the emulsion phase, while the “soluble” antigen was found in the aqueous phase. None of these antigens was found to be infectious in tissue culture. Prolonged and repeated ether treatments of the sedimentable antigen resulted in the release of more “soluble” antigen into the aqueous phase. Maximum “soluble” antigen liters were produced when crude cell pack antigen was ether treated at pH of 9. The rubella virus spedficity of the sedimentable and non-sedi-mentable CF antigen preparations were established. The non-sedimentable CF preparation was compared to myxovirus soluble antigen in the sense that this term was used to describe the internal CF antigen of the latter. The sedimentable rubella CF antigen was considered to be “soluble” antigen attached to or associated with cellular material. The authors wish to express their appreciation to Dr. Robert Huebner for advice and encouragement, to the members of the CF laboratory, Section on Infectious Diseases, and especially to Mrs. Luanne Owens, Mrs. Nancy Tzan, Miss Jean Weber, Mrs. Pernell Crockett and Miss Nannette Ratner for technical assistance.

Rubella Neutralizing Antibody Determinations with the Rabbit Kidney Cell Strain LLC-RK1

Summary The serum neutralization test utilizing the continuous line of rabbit kidney-cell strain LLC-RK1 has been found to be quite sensitive and reproducible. Some differences in results were found when neutralization tests were compared to HI tests. Performance of the HI test at an initial 1:4 dilution of serum appeared to be an important step in decreasing the possibility of false negative results. Even with this change, of 37 sera with no detectable HI antibody, 9 had antibody in the neutralization test. Clearly, there is a need to not only document serological results but to determine the true significance of these conflicting findings. These differences are important for the interpretation of serological tests for all clinical and vaccine studies.

Cultivation of rubella virus in avian tissue cultures and embryonated eggs.

Summary The cultivation of rubella virus in avian tissue culture systems, and particularly in RIF-free chick embryo tissue culture, is of importance in the development of safe attenuated rubella virus vaccines for parenteral administration. Nine virulent or attenuated rubella virus strains were propagated for at least 3 passages in RIF-free chick embryo tissue culture or duck embryo tissue culture. Several strains showed growth in duck and chick tissue through the 5th to 7th passages. Highest titers were usually obtained when passages were made at intervals of 7 or more days. Virus titers varied from 1.2 to 4.5 TCIND50 log 10/ml in duck tissue culture at the 5th to 7th passages, and 1.0 to 1.5 TCIND50 log10/ml in chick tissue culture at the 5th passage level. Virus growth was demonstrated in early passages in embryonated duck eggs but no detectable growth was obtained in chick eggs. The propagation of rubella virus in RIF-free chick embryo tissue culture warrants further efforts at the development of an attenuated rubella vaccine in this tissue culture system.

Problems in the detection of rubella virus in African green monkey kidney tissue culture.

Summary The sensitivity to rubella virus of 96 lots of AGMK tissue culture was evaluated using the enterovirus interference technique. Wide variation in sensitivity was found leading to the classification of 32 of the lots tested as resistant to rubella virus. The use of these resistant lots of tissue culture for the isolation or titration of rubella virus would lead to invalid test results. Appropriate controls are needed to assure the validity of studies in which rubella virus is detected with African green monkey kidney tissue culture.