Current knowledge of the nature of the antigens and of the host immune responses in vaccinal immunity to Marek's disease is reviewed. It is suggested that a two-step mechanism of resistance operates. The first step involves humoral and cell-mediated responses directed against viral antigens; the second step occurs after challenge with Marek's disease virus and consists of cellmediated responses directed against tumour cells. 相似文献
This paper reports the milk protein polymorphism, the allele frequencies of variants and the possible linkages among various combinations of milk protein phenotypes in the Kangayam cattle of south India. Milk samples from 156 Kangayam cows were typed by starch gel and polyacrylamide gel electrophoresis for caseins and whey proteins, respectively. All the four milk protein components studied, s1-casein, -casein, -lactoglobulin and -lactalbumin, exhibited polymorphism with high allele frequencies of 0.9231±0.0151 for s1-casein C, 0.9263±0.0148 for -casein A, 0.9135±0.0159 for -lactoglobulin B and a relatively high frequency of 0.6218±0.0275 for -lactalbumin A. The mean heterozygosity estimated over all the four milk protein loci was 0.2420. Genetic equilibrium was observed among all the loci studied, except -lactalbumin. Linkage analysis confirmed the non-independence between s1- and -caseins and between caseins and -lactalbumin phenotypes. 相似文献
Foot-and-mouth disease virus (FMDV) is an aphthovirus of the family Picornaviridae and the etiological agent of the economically most important animal disease. As a typical picornavirus, FMD virions are nonenveloped particles of icosahedral symmetry and its genome is a single stranded RNA of about 8500 nucleotides and of positive polarity. FMDV RNA is infectious and it replicates via a complementary, minus strand RNA. FMDV RNA replication is error-prone so that viral populations consist of mutant spectra (quasispecies) rather than a defined genomic sequence. Therefore FMDV in nature is genetically and antigenically diverse. This poses important challenges for the diagnosis, prevention and control of FMD. A deeper understanding of FMDV population complexity and evolution has suggested requirements for a new generation of anti-FMD vaccines. This is relevant to the current debate on the adequacy of non-vaccination versus vaccination policies for the control of FMD.
Résumé
Le virus de la fièvre aphteuse est un aphtovirus de la famille des Picornaviridae et l'agent de la maladie animale la plus importante sur le plan économique. En tant que picornavirus typique, le virus de la fièvre aphteuse est nu, sous forme d'icosaèdre et son génome comprend un acide ribonucléique monobrin avec environ 8500 nucléotides et une polarité positive. L'acide ribonucléique de ce virus est infectieux et il se réplique par l'intermédiaire d'un brin d'ARN moins, complémentaire. La réplication de l'acide nucléique de ce virus conduit à des erreurs, de telle sorte que les populations virales comprennent un ensemble de mutants (quasi espèce) plutôt qu'une séquence génomique bien définie. Par suite, le virus de la fièvre aphteuse est génétiquement et antigéniquement varié. Ceci entraîne des difficultés importantes pour le diagnostic, la prévention et la maîtrise de la fièvre aphteuse. Une connaissance plus approfondie de la complexité et de l'évolution de la population de ce virus a conduit à des besoins pour une nouvelle génération de vaccines aphteux. Ceci est lié au débat actuel sur le choix d'une politique de vaccination ou de non-vaccination dans la lutte contre la fièvre aphteuse. 相似文献
This research investigates the impact of human activities on carbon (C) dynamics in a mountainous and semi‐arid environment. Despite the low C status of drylands, soil organic carbon (SOC) is the largest C pool in these systems and therefore may offer significant C sequestration potential in systems recovering from degradation. Nevertheless, quantification of this potential is limited by lack of knowledge concerning the magnitude of and controls on regional SOC stocks. Therefore, this study aimed to (i) investigate the variability of soil organic carbon in relation to recovery period and key soil and topographical variables, and (ii) quantify the effects of recovery period following abandonment on SOC stocks. Soil profiles were sampled in the Sierra de los Filabres (southeast Spain) in different land units along geomorphic and degradation gradients. SOC contents were modelled using recovery period and soil and topographical variables. Sample depth, topographic position, altitude, recovery period and stone content were identified as the main factors for predicting SOC concentrations. SOC stocks in 1 m depth of soil varied between 3.16 and 76.44 t/ha. Recovery period (years since abandonment), topographic position and altitude were used to predict and map SOC stocks in the top 0.2 m. The results show that C accumulates rapidly during the first 10–50 yr following abandonment; thereafter, the stocks evolve towards a steady‐state level. The erosion zones in the study area demonstrate greater potential to increase their SOC stocks when abandoned. Deposition zones have greater SOC values, although their C accumulation rate is lower compared with erosional landscapes in the first 10–50 yr following abandonment. Therefore, full understanding of the C sequestration potential of land use change in areas of complex topography requires knowledge of spatial variability in soil properties and in particular SOC. 相似文献