Immunization against Aujeszky's disease. I. Extraction of the modified Aujeszky's disease virus
Arch Exptl Veterinarmed 17(6): 1325-1344
The Aujeszky's disease virus (AK) was passaged through cultures of chick embryo cells; after 200 passages in Parker-medium (PM) cultures at 36[degree]C, it was passaged either 200 or 100 times in PM and Earle-medium (EM) cultures at 36[degree]C. The 400 passages caused no diminution in the virulence of the virus for mice, guinea pigs, and rabbits, but only a modification in the clinical picture. On the other hand, the virus lost its neuropathogeny for 4-week old piglets after 200 passages in chick embryos with PM and 50 passages in EM or after 300 passages in chick embryos with PM. After 400 passages (200 each in PM and EM) the virus is harmless to sheep and calves following intramuscular injection, while the virus from the 400 passages in chick embryos with PM caused death in 50% of the test sheep. The number of passages and the composition of the culture medium is important with respect to modification of virulence, whereas temperature has no demonstrable effect. The significance of the effect of the culturing method was confirmed by further experiments with five virulent strains obtained by tissue culturing; 100 passages in chick embryo cultures with EM abolished their neurovirulence to hogs (4 strains). Single doses of the modified virus administered to pigs, calves and sheep led to the formation of antivirus antibodies at low titers only (0-16) but revaccination increased the titer (32-512).