Dynamic Study On The Antibody, Pathogen And Pathology Of Sheep Inoculated With B.Melitensis

Brucellosis caused by Brucella in the world led to huge economic losses. Most of Brucella parasitize mainly in lymphocyte and lymphatic tissue, resulting serious lesion of the immune system, followed by bacteriemia, which seriously impaired nervous system, reproductive system and skeleton system. Interactions between brucella and host need to explored in the control because of its complex type.The aims of the study were to understand the natural infection history and and the pathogenicity in tissues of B. melitensis in sheep. The10-month-old healthy sheep were inoculated with reference strain16M, One ewes and one ram were randomly selected to be euthanized at7,15,30,60,90,120,180days post-inoculation(dpi). After gross observation, tissues were collected for the pathogen detection, histopathology examination, immunohistochemistry(IHC) examination and in situ hybridization(ISH) examination. We try to tentatively demonstrated the temporal-spatial developmental patterns of pathology and pathogen distribution or dynamic change in the infected sheep, which could provide a more comprehensive understanding of the natural history for ovine Brucellosis.A transient low fever and anorexia were observed at48h dpi, and then the sheep were in the state of sub-clinical state. Gross pathological changes were limited to enlargement of the superficial lymph nodes, livers and spleens especially in the early period of infection. Lesions in immune organs riched in reticuloendothelial system were most evidence, which was most severe at7dpi and gradually returned to normal architecture at180dpi. IHC examination showed that Brucellar antigens predominantly distributed in the cytoplasm of macrophages and neutrophils in the prescapular lymph nodes, parotid lymph nodes, submaxillary lymph nodes and spleens at early stage of infection. No positive or weak positive signal was observed in other tissues. ISH examination showed that16M nucleic acids were detected in liver, spleen, lung, heart, kidney, lymph nodes, duodenum, jejunum, ileum, abomasum and testicle. The maximum detection rate of brucella-positive tissues appeared at7dpi, and brucella-positive cells could still be observed at120dpi. The macrophages, neutrophils, lymphocyte and epithelial cell in various tissues showed to be positive staining.Bacteriological examination revealed a generalized infection was induced at7dpi and progressively cleared. From120dpi, no bacteria could be isolated in any tissues collected. Meanwhile, the sero-agglutinating antibody in infected sheep was detectable at7dpi, reached a peak titer at15dpi, and then gradually reduced, the serum samples collected from the infected animals were negative at240dpi.The results of the study initially revealed the natural history of non-pregnancy sheep infected with B.melitensis. Pathological changes and pathogen distributions of the infected sheep concentrated on organs riched in reticuloendothelial system, which were more obvious at7dpi and disappeared after120dpi. Although the four detection methods in this study differed in sensitivity more or less, all of them could be used to study the pathogenic mechanism. The antigen detection results showed that ISH method was more sensitive than the classic bacterial method, while the ISH detection method may become a "Golden standards ".The conventional bacteria technology, immune pathology technology and molecular pathology technology were used to understand the natural infection history and and the pathogenicity in tissues of B. melitensis in sheep. These results tentatively demonstrated the temporal-spatial developmental patterns of pathology and pathogen distribution in the infected sheep, which could provide a more comprehensive understanding of the natural history for ovine Brucellosis.