Simple and rapid method for production of whole-virus antigen for serodiagnosis of caprine arthritis-encephalitis virus by enzyme-linked immunosorbent assay.

Polyethylene glycol (PEG) was used to produce whole-virus antigen derived from tissue culture cells infected with a Canadian strain of caprine arthritis-encephalitis virus. PEG antigen batches were obtained after precipitation and concentration of infected tissue culture material with PEG 8000 and final treatment with sodium dodecyl sulfate. The optimum time of harvest of tissue culture extracted material to produce the maximum amount of viral proteins was determined in roller bottles, after cocultivation of infected and noninfected fetal lamb corneal cells. Samples from day 9 to day 25 postculture were collected and processed. By Western blotting, the optimum time of harvest was found to be day 25 following the coculture. Two large batches of PEG antigen were prepared at the optimum time of harvest. Both batches gave similar results when tested by Western blotting and enzyme-linked immunosorbent assay (ELISA), using reference control sera from infected and noninfected goats. For further testing in ELISA, cutoff values and ratios were determined for PEG batch 1, using 200 known serum samples from goats free of the disease. The PEG antigen batch was compared with an in-house ELISA antigen in a kinetic mode, using 498 serum samples from field goats. The in-house ELISA antigen was produced following two rounds of ultracentrifugation and treatment with sodium dodecyl sulfate (R. A. Heckert, W. B. McNab, S. M. Richardson, and M. R. Briscoe, Can. J. Vet. Res. 56:237-241, 1992). The PEG antigen batch was found suitable for ELISA, with a relative specificity of 100% and a relative sensitivity of 99.4% compared to the in-house ELISA antigen. This method of antigen production for ELISA was found to be rapid, inexpensive, and reliable for the diagnosis of caprine-arthritis encephalitis, without requiring the use of sophisticated laboratory equipment.