Study On Dynamic Distribution Of Highly Pathogenic PRRSV In Infected Piglets And Its Proliferation Characteristics In Vitro

Porcine reproductive and respiratory syndrome (PRRS) is caused by porcine reproductive and respiratory syndrome virus (PRRSV). It is a important infectious disease of swine which is characterized by severe reproductive failure in sows and respiratory distress in piglets and growing pigs. Since it first reported in the United States in 1987, after popularing in North America and Europe country, it has been spred quickly to most countries. During the 2006"Swine High FeverDisease"outbreak in China. The results of the present study indicate that PRRSV mutant was one of the main etiologies, and mixed infection with many pathogen, it is characterized by high-fever. Since it was founded in 1987, The PRRS has caused huge economic losses to the swine industry worldwide To understand the kinetics and distributed characteristic of highly pathogenic PRRSV mutant strain (HuN4 strain) in piglets, the tropism of virus in the organs of piglets was investigated. The 40-day-old healthy piglets were inoculated with the HuN4 strain and its attenuated strain HuN4-F65. In each group two piglets were slaughtered on 3, 5, 7, 10, 14, 21 and 28 days post-inoculation(dpi)respectively. The viral load of PRRSV in brain, tonsil, submandibular lymph node, inguinal lymph nodes, mesenteric lymph node, heart, spleen, kidney, lung, liver, stomach, duodenum and serum were detected by fluorescence quantitative PCR. The results showed that the viral load in HuN4 group was significantly higher than that in HuN4-F65 group, peak of the viral load in HuN4 group appeared on 7 dpi, and downward trend appeared at the later stage. The HuN4 strain was widely distributed in vivo, and the persistence on 21 dpi, viral load of various organs showed normal distribution, however, the viral load of serum in HuN4-F65 group appeared lower, and focus on monocyte-macrophage cells relatively dense of tonsil and submandibular lymph nodes, compared with lung of main tropism to organs of the HuN4 strains has changed. In addition, this study also observed histological lesions of piglet were inoculated the mutant PRRSV using the method of HE staining and to explore relationship between viral load and histological lesions in the various organs of piglet. The results showed that histological lesions of various organs were obvious in HuN4 group, but it was minor in HuN4-F65 group. There was correlation between viral load and histological lesions in HuN4 group, tonsils, lymph nodes and spleen were correlation between viral load and histological lesions in HuN4- F65 group, while the other organs were no correlation between viral load and histological lesions in HuN4- F65 groupTo study the kinetics of HuN4 strain and HuN4-F65 strain in vitro of different cell using fluorescence quantitative PCR method. The results showed HuN4 strain and HuN4-F65 strain can replication in the Marc-145 cell, the replication of HuN4-F65 strain was the most efficient in the Marc-145 cell. For the PAM, HuN4 strain was tropic strains in the PAM, whereas HuN4-F65 strain replicationed within a small increase in the PAM. The virus had no significant replication in the cell, after PIEC was infected with HuN4 strain and HuN4-F65 strain...