Tissue Distribution Of The Latent PRV In The Pigs

Pseudorabies virus (PRV) is the causative agent of pseudorabies (Aujeszky's disease), a serious infectious disease of several domestic and wild animals. The natural host and reservoir of this virus is pig. And it is often epidemic infection in pigs. Since pseudorabies was first reported in 1902, it has spread throughout the world and has caused enormous economic losses to our country and even global pig industry. It was one of the most harmful diseases of the pork-producing industry. Therefore, it is urgent at present to prevent, control and eliminate this disease. Like other alpha herpesvirus such as herpes simplex virus type I, varicella-zoster virus and bovine herpesvirus type I, PRV also has the typical characteristics of alpha herpesvirus, including latency and neurotropism. PRV is advantageous to the research of the production and distribution, neurotropism and pathogenesis of alpha herpesvirus, and the evaluation of immune response and new vaccine. Therefore, PRV is an excellent model for herpesvirus's biology.To establish a PRV latency model, four-week-old piglets whose sera were negative tested by PRV-ELISA method were purchased. Three days after purchase, the piglets were immunized with an inactive oil emulsion vaccine for the first time, and for the second time two weeks later. Simultaneously, the blood was obtained from piglets' precaval vein, and the antibody was tested by serum neutralization test. When the serum neutralization titers reached≥1:2, the vaccinated piglets were intranasally challenged with 2mL of PRV strain gG^-/LacZ⁺ (TCID₅₀=10^-6.5/0.1mL). The pig's nasal swabs were collected separately twice a day after PRV challenged, and their body temperature was measured at the same time. Nasal swabs were tested by PCR, which primer designed according to the PRV gD gene. The resultes show that the PRV could not be discovered 4 days post infection (dpi). At 40dpi, two of the piglets were intramuscular injection administrated with dexamethasone in a dosage of 2mg/kg body weight.In order to study the tissue distribution of PRV during its replicative and lantent infection, the infected pigs were killed with the carotid artery bloodletting at 0dpi, 7dpi, 14dpi, 21dpi, 28dpi, 35dpi and so on. The brain, cerebellum, brain stem, trigeminus ganglion, optic nerve, tonsil, lung, kidney were collected separately. A part of them were stored at -80℃for RNA and DNA analysis, and the other parts were fixed in 4% paraformaldehyde as quickly as possible. After dehydration with the series density ethyl alcoholdehydration, transparent with the xylene, and embedding with the conventional paraffin wax, the wax was slice into small piece, and the thickness is 5 mm. Then it was divided into two groups, one group was make conventional hematoxylin-eosine staining(HE) (sticks tablet by the protein glycerine), and another group was make streptavidin-biotin-peroxidase complex (SABC) staining (sticks tablet by the polylysine). The results of H.E staining indicates that it has symptom of the typical non- suppurative encephalitis in brain; blood vessel react in cerebellum; withering in optic nerve; denaturation and necrosis of nerve cells; lymphocyte necrosis in the tonsil and reduced the figure; interstitial pneumoni in the lung, raised quantities of lymphocyte necrosis in the lung and renal glomerulus were withers, lymphocytes were infiltration in the kidney. The pathologic lightened after the pigs infect with PRV, with the time going. However the pathologic get worse after dexamethasone treatment. The results of SABC dying shows that there were positive cells in brain cortex, cerebellum, brain stem, trigeminus ganglion, optic nerve of the nervous system and tonsil, lung, kidney during the process of infection. And quantities of the positive cells lessen with the time going, while increased after treatment with dexamethasone. The virus was found both in the cytoplasm and nucleus of infect cells, but mostly in the cytoplasm. The positive cells were not found in all collected tissue of the negative control pigs.The observation and comparison of the staining of SABC and H.E reveals that the tropism of PRV and the regularity of tissue distribution with the infection, and the time rule of PRV in the cell and tissue. This research provides important histological data for studying PRV latency.