Histopathology And Dynamic Distribution Of Classical Swine Fever Virus In Chronically Infected Pigs

Classical Swine Fever (CSF) is caused by the classical swine fever virus (CSFV) and is a highly fatal and contagious viral disease of worldwide importance. In this study, histopathological changes during chronic infection of classical swine fever,tissue tropism and viral nucleic acid load dynamic distribution of secondaryvirulence of CSFV strain were observed, which reveal the characteristics of pathogenicity of the CSFV secondary virulence strain HeBHH1/95, and provide some experimental basis to further explore the pathogenesis of CSF infection. In this study,1130-day-old healthy weaned piglets were challenged CSFV secongdary virulence strains HeBHH strain(titer5×103.5TCID50/ml) by intramuscular injection,a model of classica swine fever chronic infection was instituted,meanwhile,the negative control of2piglets was establishment,the temperature should be measured and the clinical symptoms should be recorded by score daily after infection.1or2infectionpigs were killed in the ldpi,3dpi,6dpi,10dpi,15dpi,25dpi,35dpi,45dpi,varied organs and vitro secretions total of30kinds were collected, each sample were multiple backuped, one of which was used to HE staining and immunohistochemistry assay,and one was used to detect CSFV nucleic acid load of organization by relative of FQ-PCR assay.The chronic infection process could be divided into three parts according to clinical score and temperature trends, including the incubation period (1dpi～7dpi), diseased period (8～24dpi),regression period(25～45dpi).The temperature of infected pigs was nomal in the incubation period,there were no obvious clinical symptoms,and sacrificed the infected pigs,no lesions were found.The temperature gradually rise to41.5℃in the diseased period,the clinical manifestation were mental fatigue.loss of appetite,diarrhea,redness of armpit skin, enlargement of lymph nodes.There could be found bleeding of all lymph nodes,slight infarction of spleen and bleeding spots in the surface of kidney in infected pigs. The temperature became to drop,and the clinical symptoms gradually disappeared. In the regression period, the temperature and appetite became to nomal,except occasional diarrhea,there was no other disease symptoms.Sacrificing infected pigs in this period,it was found only slight hemorrhage and edema in lymph nodes,but no lesions in other organs.It could be found that after HE staining of histotomy,3days post infecti on,lymph nodes of inguen and submaxillary lymph nodes began to grow infilt ration of inflammatory cells,micro-thrombosis; infiltration of erythrocyte and in flammatory cells could be found around the trabecula of spleen; infiltration of inflammatory cells in the mucous membrane of tonsil, lymphocyte degenerstio n in the lymphoid nodules, but no lesions could be found in other organs; Wit h the development of diseases, other tissures gradually developed histopathological changes.15th day post infection, all kinds of tissures had histopathological changes of different degree, such as microvascular bleeding, thrombus forming and infiltrat ionof inflammatory celland histiocyte necrosis.In the latter period(35dpi and45dpi), most tissures had returned to normal station without clear histopathological changes a part from immune organs,kidney,liver and duodenum with slight histopathological cha nges.We can deduce that in the latent period, parts of immune organs has develop hist opathological changes although the pigs have no clear clinical symptom;in the onset p eriod, all tissures or organs develop classical CSF histopathological changes;in the pro gnostic period,most organs has returned to normal station apart from some organs hav e slight histopathological changes.The immune organs firstly develop histopathologic al changes and can’t be recovered during the whole disease period.We can conclude from the results of IHC that all tissues and organs were not found CSFV positive cells1days post infection; spleen, tonsil, inguinal lymph nodes, lymphonodi mesenterici, ileocecal valve and ileum were firstly found CSFV positive cells3days post infection;6days post infection, liver, stomach, duodenum, spleen, colon, rectum and kidney could aiso be found positive cells; and10days post infection-45days post infection, all samples were found CSFV positive cells. It is suggested that at the beginning of chronic CSF infection, CSFV were mainly situated in lymphocytes of peripheral immune organs and mononuclear cells or macrophages, and diffused to other tissues or organs by blood circulation. With the development of diseases, the CSFV infected cell types and the number of positive cells absolutely increased.15days post infection, samples were all found lots of CSFV positive cells including all kinds of tissues and lymphocytes. During the prognostic period, infected cell types didn’t change and CSFV positive materias could be seen in various cells although the number of positive cells decreased,among which immune organs, kidney, liver and spleen had a slightly decresing and other tissures and organs had a soar decreasing.We can conclude from the results that during the whole chronic infection period, the number of CSFV in all samples increased from latent period to onset period and then decreased in recovery prognostic period. However, the decreasing degrees varied different cells. What’s more, the results of viral nuclear detaction consented to IHC results. Medium viral CSFV strains infection powers lowered from spleen, submaxillary lymph nodes, ileum, inguinal lymph nodes,tonsil, lymphonod i mesentericipancreas,kidney,skin,lung, ileocecal valve, jejunum, liver, esophagus, s tomach,colon, testis, duodenum, urinary bladder, rectum, cardiac muscle, spinal cord, muscle to brain. Meantime, it is suggested that chronic infectious pigs can shed virus after detecting CSFV in urine, feces and saliva.In summary, we can deduce the features of medium virol strain HeBHHl/95. during the whole chronic infection period, with the incresing of virol load from thelatent period to onset period, all kinds of tissures’clinical symptom and histopathologic changes aggravated, in recovery period, the virus gradually adapted the body by the interaction bettween viruses and body. The virus can be symbiotic with the cells and the clinical symptoms gradually disappeared. Apart from immune organs and minority of tissures still had slight pathological changes, most had recoverd to normal station which finally become the CSFV carriers.