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After presenting the definition of immunosuppression the paper concentrates on the immunosuppressive properties of porcine circovirus type 2 (PCV2). Its role in the etiology of the post-weaning multisystemic wasting syndrome (PMWS) and the other porcine circovirus diseases (PCVD) is characterized, indicating that following the immunosuppressive action of PCV2 facultatively pathogenic microorganisms join the etiology of the disease syndrome which becomes multifactorial. The lymphocytopenia resulting from PCV2 infection is particularly manifest among the B lymphocytes, followed by the T lymphocytes. In vivo analyses have shown that PCV2 is most frequently associated with monocytes, macrophages and dendritic cells (DC). PCV2 infection of macrophages and DCs is the key factor determining the consequences for immune defense competence. The differences between conventional DCs (cDCs) and plasmacytoid DCs (pDCs) are mentioned. The term cDCs defines cells with antigen presenting functions and the term pDCs represents the interferon, type 1 producing cells. Examples of immunosuppressive action of other pathogens have been presented. Classical swine fever virus inhibits the interferon production in the infected DCs. In addition it causes leucopenia. These changes enablr opportunistic Pasteurella multocida and Streptococcus sp. strains to cause septicemia in the infected pigs. Immunosuppressive action of pseudorabies virus is mentioned resulting in secondary infection by other species of viruses or bacteria. Moreover, as presented in the paper, porcine reproductive and respiratory syndrome virus demonstrates immunosuppressive properties.
The definition of the porcine respiratory disease complex (PRDC) is presented and compared with diseases caused by a single etiological viral or bacterial agent. The classification of viruses or bacteria participating in the multifactorial etiology of disease complexes, among them PRDC, include microorganisms initiating the pathological process, as well as a second group of microorganisms, following after the primary destruction of the resistance to infection, that joins in the pathogenesis of the pathological complex. Another grouping takes into account the higher and lower importance of the etiological agents in causing disease and losses in animal production. The role of the following microorganisms participating in the etiology of PRDC is defined as follows: Porcine reproductive and respiratory syndrome virus, Swine influenza virus, Aujeszky disease virus, Porcine circovirus type 2, Porcine respiratory corona virus, Porcine cytomegalovirus, Mycoplasma hyopneumoniae, Bordetella bronchiseptica, Pasteurella multocida, Haemophilus parasuis, Streptococcus suis, Actinobacillus suis, Arcanobacterium pyogenes and Salmonella spp. Data on simultaneous bacterial-bacterial interactions, viral-viral interactions, and bacterialviral interactions are discussed.
This article is a review of recently published papers dealing with the possible participation of TT viruses in the multifactorial etiology of disease syndromes, particularly in postweaning multisystemic wasting syndrome (PMWS) of swine. The information concerning the taxonomy of these viruses is presented. The virus strain of this group was demonstrated for the first time in 1997 in a human in Japan and was called TTV in reference to the initials of his name. Recently the International Committee of Taxonomy of Viruses has established a new meaning of TT, namely Torque teno virus, deriving from the Latin terms “torque” meaning “necklace” and “tenuis” meaning “thin”. These terms were chosen to reflect the shape of the TTV genome. TTV was classified to the Anellovirus genus of the Circoviridae family. It was stated that there is no evidence of a link between TTV infection of humans and specific diseases. The same was true in relation to infection of cattle, sheep, chickens, dogs, cats and swine infected by other TTV strains, specific in its replication for a particular species of animals. The following text deals particularly with the last mentioned species. Globally TTV infection is widely spread in pigs. Animals, among them pigs, remain infected and even viremic for years without any apparent negative effects. However, in coinfection with porcine circovirus type 2 (PCV2), being the main etiological factor of PMWS, TTV may possibly contribute to the development of the clinical course of the disease. This is more evident in gnotobiotic pigs. In case of an infection exclusively with TTV in gnotobiotic pigs no clinical symptoms occur. However post mortem pathological changes including thymic atrophy, glomerulonephropathy and modest lymphocytic to histiocytic infiltrates in the liver are found. Summarizing, research concerning the role of TTV in the multifactorial etiology of disease syndromes needs to be continued.
The paper reviews literature that evaluates the importance of the following groups of viruses in the etiology of diarrhea in pigs, that occur mostly from birth to weaning. These are as follows: Adenoviruses, Rotaviruses, Reoviruses, Picornaviruses, Enteroviruses, Caliciviruses and Astroviruses. Their common properties are: usually low and facultative pathogenicity, dependent on the level of innate immunity of the animal; participation as one of the factors of a multifactorial etiology, usually together with several taxonomically different viruses; contribution to the emergence of clinical symptoms in pigs, together with an unsatisfactory level of welfare which frequently occurs in large farms based on industrial technologies; very often occurring symptomless infections and carriership of these opportunistic microorganisms in healthy animals. These microorganisms predominantly represent RNA viruses and express a high frequency of variability of their genomes. As a consequence this may contribute to the emergence of new species, quasi-species, or variants in the enumerated groups of viruses, in addition to variants also pathogenic for humans. At present it is difficult to define which species or variants of the mentioned groups of viruses - besides the mentioned environmental factors - initiate the multifactorial, enteric disease of pigs. However it may not be excluded that Torque teno or PCV2 viruses and some bacterial enteropathogens, particularly E. coli serotypes pathogenic for swine, may be taken into account.
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