Establishment of the attenuated strain of porcine parvovirus for the live vaccine and its biological-immunological characteristics.

Abstract

When the 90HS strain of procine parvovirus (PPV) was subjected to passages in embryonic swine kidney cell line (ESK cells), the low virulent HT- strain was obtained. When it was subjected continually to passages in primary swine kidney cultured (SK) cells at low temperature, attenuated HT-/SK strain as live virus vaccine was established. The ability of the HT-/SK strain to multiply in vitro was the highest at 32°C. The strain which multiplied at this temperature showed more than 3000 times as high an infective titer as that which multiplied at incubation of 37°C or 40°C. To examine the safety of the HT-/SK strain, 4-months-old piglets and pregnant sows negative for antibody were inoculated with this strain. No piglets or sows presented any abnormal clinical sign, viremia, or discharge of virus, or involved in contact infection. These swines showed complete ability of defense against challenge by intranasal inoculation with PPV of field strain. The pregnant sows immunized with the HT-/SK strain were challenged with PPV field strain to examine an effect of preventing fetal infection. They gave birth, however, to normal piglets, which were negative for serum antibody against PPV before sucking of colostrum. Therefore, no fetal infection was induced by high virulent field virus. On the other hand, abnormal young were born from a nonimmunized control sow. Virus was recovered from stillborn fetuses from this sow. Thus, it was considered that this strain could be used as attenuated live vaccine for prevention of PPV.