Isolation, Identification Of Porcine Reproductive And Respiratory Syndrome Virus RX Isolate And Study On Chinese Herbal Medicine Against PRRSV RX

Isolation ,identification of Porcine Reproductive and Respiratory Syndrome Virus(PRRSV) from Guangdong were performed in this study. One virus strain was successfully isolated from the tissues of pigs which were preliminarily diagnosed to be infected with PRRSV, designated RX. The isolate can proliferated on Marc-I45 cell line. After three passages, apparent CPE were observed in Marc-145 cell.Further experiments were done to identify the isolate. A large number of global particles (40-60nm in diameter) were observed under electron microscope. The TCIDS0 was 10-4.5/0. 1 ml. When the virus was treated at 56℃for 20-30 min ,the virus lost the ability to infect Marc-145 cell line. Slight improvement of body temperature and respiratory syndrome appeared when 40-day-old piglets were inoculated with the isolate. Above experiments proved the isolate to be PRRSV.Six Chinese herbs such as Radix Astragali, Radix isatidis ,Radix Glycytthizae, Herba Houttuyniae ,Fructus Crataegi and Herba Artemisiae Annuae were used in anti-virus experiment in vitro. The Chinese herbs were Separately decocted and concentrated by heating to a final concentration of 100mg/ml respectively. All the drug-liquids were sterilized by autoclave and stored at 40C .In the Marc145ell culture experiment in vitro, the cytotoxic influence of different concentrations diluted at multiple proportions was studied to determine the highest non-toxic concentration, and anti-virus mechanism of the effective anti-PRRSVwas studied in three ways: adding medicine to the cultured Vero cell before adding virus, adding virus to the cultured Vero cell before adding medicine, and adding medicine and virus to the cultured Vero cell after they acted for a while. Antiviral activity against PRRSV was estimated in terms of Cytopathic effect, viral titre yields and OD values of MTT colorimetric method to determine the respective effects of anti-penetration activity against virus, restraint of virus propagation and direct destruction of virus , respectively. The results were as follows.The highest non-toxic concentrations of medicaments were(mg/ml): Radix Astragali 12.5 mg/mL,Radix Glycytthizae3.125 mg/mL,Herba Houttuyniae 3.125 mg/mL,Fructus Crataegi 1.526 mg/mLand Herba Artemisiae Annuae1.526 mg/mL.The best medicines in the three ways were screened out. Radix Glycytthizae and Herba Artemisiae Annuae provided good protection for cell. The protection rates of amantadine and neutral acriflavine were over 80% and this showed that they had better effect than Chinese herbal extracts.