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Although the “stamping-out” policy in combination with movement and trade restrictions of poultry and poultry products are the major methods of avian influenza (AI) eradication, especially its highly pathogenic form (HPAI), vaccination can be considered as a valuable tool in AI control. The international regulations allow for the implementation of vaccination policies with strict provisions. One of the major components of the vaccination program should be “DIVA” (“Detecting Infected from Vaccinated Animals”) strategy. DIVA is a concept allowing the detection of infection in a vaccinated population of animals. It consists of the application of sentinel birds, vaccines and DIVA companion serological tests differentiating post-infection from post-vaccination antibodies. At present, inactivated vaccines are most commonly used, but other vaccines such as recombinant vector or DNA vaccines have also been licensed and utilized. Vaccination against HPAI H5N1 has been used most extensively in Asia, especially in the People’s Republic of China, and to some extent in other parts of the world, including Europe. Countries which have the experience of poultry vaccination to combat AI caused by subtypes other than H5N1 include: Italy (H7N1, H7N3), Mexico (H5N2), USA (numerous subtypes).
Infectious bursal disease (IBD) is a highly infectious and contagious immunosuppressive viral disease of chickens with a worldwide economic significance to the poultry industry. Over fifty years have passed since the first confirmed occurrence of the disease, and the virus has spread all over world and evolved into multiple genetic, antigenic and pathotypic variants, becoming a serious threat to the poultry industry. The primary tool in IBD eradication is the maintenance of strict biosecurity in poultry farms and implementation of vaccination programmes which should take into account the current epidemiological knowledge about the IBDV strains circulating in the field. This review article presents the current state of knowledge about the infectious bursal disease virus (IBDV) with special regard to the molecular biology of the virus, immunological aspects, as well as current and future prevention strategies.
The paper reviews molecular markers and determinants associated with virulence, host adaptation and drug resistance in avian influenza viruses (AIV). The virulence of AIV is mostly dependant on the presence of multiple amino acids (mainly arginine and lysine) at the cleavage site of the haemagglutinin (HA) protein. The major factors contributing to host adaptation are also harbored within the HA protein: amino acids at positions 226 and 228 determine virus binding affinity to receptors present in cell membranes of birds or humans. It has been shown that pathogenicity and host adaptation are also dependant on the amino acid sequences of the polymerase complex (PB2-PB1-PA) and the most significant mutation (E627K in PB2) is related to the increased replication of the virus in mammalian cells. Molecular markers associated with an increased resistance to antiviral drugs are localized in neuraminidase (NA) and matrix (M) proteins. For example, a histidine to tyrosine substitution at position 274 of NA (H274Y) decreases viral susceptibility to neuraminidase inhibitors (e.g. oseltamivir), the most frequently used drugs in flu treatment. Monitoring of the molecular changes in the viral genome of AIV is very important from an epidemiological point of view and can be a valuable part of an early warning system.
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In this study, a pigeon paramyxovirus type 1 (PPMV-1) isolated from a flock of ornamental pigeons in Poland in 2010 is described. The PPMV-1/Poland/H2/10 isolate showed the amino acid sequence at the cleavage site of F2/F1 ¹¹²KRQKRF¹¹⁷ i.e. typical of virulent strains. Despite having the monoclonal antibody binding pattern typical of pigeon variants PPMV-1 (antigenic group “P”), the Polish isolate clustered into genetic sublineage 4a, which is usually associated with PMV-1 isolated from poultry.
The aim of the study was to compare immunoperoxidase (IP) and Antigen-Capture ELISA (AC-ELISA) tests in detecting infectious bursal disease virus (IBDV) in the Fabricius Bursa (BF) of infected chickens. BFs were collected for 3 days p.i. with IBDVs of low pathogenicity (isolated from a mild form of IBD) as well as very virulent ones (isolated from an acute form of IBD) 1, 3, 6 and 9 days p.i. with vaccinal, low pathogenic and very virulent strains. BFs from broiler chickens suspected of having IBD were also used. BFs were cut into frozen histological sections and, after fixing with formaldehyde, were stained using the IP method. The remainder of BFs was used in AC-ELISA after homogenization and clarification. The sensitivity and specificity of both tests in detecting IBDV antigens were comparable but the amount of viral antigen could be determined only by using the AC-ELISA method. The intensity of reaction and the time during which the viral antigen was detected were strongly correlated with the pathogenicity of the IBDV strain being used. Inoculation with the vaccine strain yielded positive results only on day 6 p.i. and the amount of detectable antigen was very low. Infection with the low pathogenic Polish strain produced more antigens, detectable from days 1 to 6 p.i. The antigen of the very virulent strain was found in the largest amount and could be detected for 9 days beginning on day 1 p.i. The study indicated that the IP method is simple, rapid and less laborious than AC-ELISA. However, AC-ELISA is more useful because it additionally measures the amount of detected antigen in a specimen.
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