Pathogenic Analysis Of HP-PRRSV In Experimentally Infected4-month-old Laiwu Black Pigs

Porcine reproductive and respiratory syndrome (PRRS) is caused by porcine reproductive and respiratory syndrome virus.PRRSV infection can cause pregnantsow late abortion, premature and stillborn, piglets and fattening pigs, respiratory disease.In the summer of2006, HP-PPRS first took place in southern China. So far, it has caused unprecedented damage to our country’s pig industry.HP-PRRSV will cause more serious stillbirth, abortion of pregnant sows.Laiwu black pig is a type of local breeds in North China, Shandong Province, a typical representative of the local black pig, with the adaptability, high reproduction rate, tender and delicious meat, etc., is a valuable gene pool of native pig breeds in China. The survey found that, in the process of the epidemic, the rare incidence of Laiwu black pig or mild, with a certain degree of natural resistance.Fore-month-old healthy Laiwu black pigs were inoculated nasally with HP-PRRSV. The pigs were necropsy on different day post inoculation. The antibodies level titer of peripheral blood serum were tested by ELISA test kits (IDEXX). Tissues were collected for preparing tissues sections. Pathological changes of different tissues were observed through HE staining. Immunohistochemistry(IHC) protocol were developed to detect distribution of HP-PRRSV antigens in tissue samples. The results showed that slight symptoms can be seen2days post-infection, lasting two days before disappearing and no pigs died. Antibodies can be detected5days post-infection (1/7), and reached the peak14days post-infection. Histopathological changes show that interstitial pneumonia, slight viral encephalitis and particles degeneration of essence organs occurred in pigs3days post inoculation;7days post inoculation shows typical interstitial pneumonia, necrosis of the lymphoid organs,eosinophilic cells infiltration in intestines and parenchymal organs appear vacuolar degeneration. From2weeks to4weeks post inoculation typical interstitial pneumonia were found in lung, and the viral encephalitis becoming seriously, necrosis in adrenal, inflammatory cells infiltrating in pancreas slightly, serious congestion and hemorrhage were found in thyroid and parenchymal organs appear vacuolar degeneration acutely. PRRSV antigen-positive signals can be seen in lymphoid tissue (lymph nodes, spleen, tonsils), trachea, heart, liver, lung, kidney, stomach, duodenum, jejunum, ileum, thyroid, adrenal gland, submandibular gland, uterus, brain and cerebellum; cecum, colon, rectum, bladder, pancreas, fallopian tubes and ovaries were not seen positive signals. Positive signals were mainly located in the cytoplasm of infected cells, occasionally in the nucleus. This experiment confirmed that4-month-old Laiwu black pigs infected HP-PRRSV can cause a wide range of tissue tropism and extensive tissue damage, while clinical symptoms are mild;no mortality;4-month-old Laiwu black pigs have a strong resistance to HP-PRRSV. The results provide a theoretical basis to study the differences in the pathogenicity of HP-PRRSV between our local species of pigs and the foreign ones.