A STANDARDIZED SERUM NEUTRALIZATION TEST FOR FELINE VIRAL RHINOTRACHETITIS .2. VIRUS-SERUM SYSTEM

A standardized protocol for testing feline viral rhinotracheitis is given. Stock virus is best held in freeze-dried aliquots at -5°C. for up to 1 year, and diluted when required in tissue culture medium, supplemented with 10 per cent. heat-inactivated calf serum, to contain 103 TCID50/ml. Test sera, heat-inactivated at 56°C. for 1 hour and stored at -5°C. are serially diluted by 2-fold steps and mixed in equal volumes with diluted virus suspension. Incubation proceeds at 37°C. for 1 hour and overnight (18 hours approximately) at 4°C. Subsequently, 0·2 ml. of serum/virus mixtures are inoculated into feline cell monolayers or suspensions using 2 tubes per dilution and incubated at 37°C. The test is read at approximately 3 days when a negative serum control shows a maximum CPE, and endpoints are calculated as the final dilution of serum at which 50 per cent. of inoculated monolayers would show complete neutralization of virus. A known reference serum is tested simultaneously. © 1969.