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排序方式: 共有18条查询结果,搜索用时 15 毫秒
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A single dose of 5 x 10(8) bacilli of Pseudomonas pseudomallei by intratracheal injection resulted in acute (21 cases) or chronic (19 cases) melioidosis in 40 of 48 pigs. Fifteen (10 acute and 5 chronic) had been immunosuppressed by cyclophosphamide before inoculation. The major clinical signs were initial fever, marked neutrophilia and, in the acute cases, respiratory distress. There were no signs of the nasal and ocular discharge, paresis or diarrhoea seen in acute cases in south-east Asia. The cyclophosphamide treatment caused a significant decrease in the neutrophil count by 7 d after inoculation in all 15 immunosuppressed pigs, and all were culture positive at necropsy. Eight of the 33 non-treated pigs were culture negative at necropsy. Pigs overcoming the initial phase of infection had more abscess-like nodules that were bacteriologically sterile at necropsy than the pigs with acute cases of melioidosis. P. pseudomallei was isolated predominantly from the spleen, lungs and the injection site. Although only one strain was used in this study, it is likely that Australian strains of P. pseudomallei are not as virulent as the south-east Asian isolates.  相似文献   
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Wang K  Riggs RD  Crippen D 《Phytopathology》2005,95(8):890-893
ABSTRACT The reniform nematode, Rotylenchulus reniformis, is a serious threat to cotton (Gossypium hirsutum) production in the United States, causing an annual loss of about $80 million. The objective of this study was to isolate fungi from eggs of R. reniformis and select potential biocontrol agents for R. reniformis on cotton. We focused on the fungus Pochonia chlamydosporia because it suppresses root-knot and cyst nematodes and because preliminary data indicated that it was present in Arkansas cotton fields. Soil samples were collected from six cotton fields in Jefferson County, Arkansas. A total of 117 isolates of the nematophagous fungus P. chlamydosporia were obtained. In an in vitro test, 105 of the 117 isolates parasitized fewer than 15% of R. reniformis eggs, but 12 isolates parasitized between 16 and 35% of the eggs. These 12 isolates produced from 6.8 x 10(4) to 6.9 x 10(5) chlamydospores per gram of medium in vitro, and chlamydospore production was similar on rice grain and corn grain media. In two greenhouse experiments, a single application of isolate 37 (5,000 chlamydospores per gram of soil) significantly reduced the numbers of R. reniformis on cotton roots and in soil. The three isolates (37, 26, and 14) that parasitized the most eggs in vitro were also the most effective in suppressing numbers of R. reniformis and in increasing cotton growth in the greenhouse.  相似文献   
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Effects of small population size and reduced genetic variation on the viability of wild animal populations remain controversial. During a 35-year study of a remnant population of greater prairie chickens, population size decreased from 2000 individuals in 1962 to fewer than 50 by 1994. Concurrently, both fitness, as measured by fertility and hatching rates of eggs, and genetic diversity declined significantly. Conservation measures initiated in 1992 with translocations of birds from large, genetically diverse populations restored egg viability. Thus, sufficient genetic resources appear to be critical for maintaining populations of greater prairie chickens.  相似文献   
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The objectives of this study were to determine effects of cyfluthrin and pyrethrin spray products, used in combination with cyfluthrin topical and ear tag applications, on bull reproductive parameters over 18 weeks. Angus or Angus x Simmental bulls were randomly assigned to one of three treatment groups: (i) no exposure to pyrethrins/cyfluthrin (CONT; n = 10), (ii) cyfluthrin ear tag and topical applications (ET; n = 10), or (iii) cyfluthrin ear tag, topical, premise spray and pyrethrin fog spray applications (ET+S; n = 8). Bull body weight was measured every 3 week, and body condition score and scrotal circumference were recorded on weeks 0, 9 and 18. Semen and serum were collected every 3 weeks for sperm evaluation and testosterone measurement, respectively. There was a treatment × week interaction (p < 0.01) for sperm with primary defects; bulls in CONT group had a greater (p = 0.01) percentage of sperm with primary defects than bulls treated with insecticides at week 18. Overall and progressive sperm motility, normal sperm morphology, secondary sperm defects and serum testosterone concentrations changed (p < 0.01) over time in all bulls; however, treatment did not affect (p ≥ 0.13) any of these parameters. There were also no treatment effects (p ≥ 0.08) on bull body weight, body condition score or scrotal circumference. The use of pyrethrin‐ and cyfluthrin‐based insecticides, regardless of application, did not negatively affect reproductive parameters in beef bulls when administered over 18 weeks.  相似文献   
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There is need to determine the nature of enduring reservoirs of Salmonella contributing to perpetual contamination within poultry flocks. The dispersal of Salmonella between birds, litter and the lesser mealworm has been established, but the extent that these act as critical components in the epidemiology of Salmonella infection during broiler grow‐out and flock rotation has not been delineated; in particular, the level of participation by the lesser mealworm beetles (LMB) as agents of retention and dispersal. This study defines this route of transmission and provides empirical data on bacterial loads that facilitate Salmonella transfer. Results showed differential Salmonella transfer dependent on bacterial concentration. At 103 cfu/ml, only a small, but not significant, amount of Salmonella was transferred, from the LMB to the manure and back to uninfected LMB; while from 105 to 107 cfu/ml, a significant acquisition and transfer occurred both internally and externally to the LMB over 4 and 24 hr exposures. These data will be used in correlation with facility management practices to develop intervention strategies to mitigate the establishment and spreading of reservoir Salmonella populations contributing to pre‐harvest contamination of poultry flocks.  相似文献   
7.
Previously unknown strike-slip and normal faults in the central and eastern Mojave Desert have been revealed on Landsat Thematic Mapper images enhanced by four-component processing. This method provides color images on which lithologies are discriminated by their contrasting absorption and reflection, primarily at infrared wavelengths and particularly with regard to their ferric iron, ferrous iron, and hydroxyl contents, while retaining landform depiction. These discriminants represent a new type of geophysical display for geologic mapping in regions of well-exposed bedrock. Faults are revealed on the images by abrupt spectral and textural contrasts that coincide with aligned topographic features. The newly discovered faults form part of an extensive regional network of right shear that connects faults in the Death Valley region with the San Andreas fault system. They support a heterogeneous strain model for late Cenozoic tectonic evolution of the region. Regional structural relations indicate a westward migration of the locus of strain through time. Some of the newly identified faults bound blocks that have experienced contrasting rotational histories since early Miocene time.  相似文献   
8.
Local control of the domain orientation in diblock copolymer thin films can be obtained by the application of electric fields on micrometer-length scales. Thin films of an asymmetric polystyrene-polymethylmethacrylate diblock copolymer, with cylindrical polymethylmethacrylate microdomains, were spin-coated onto substrates previously patterned with planar electrodes. The substrates, 100-nanometer-thick silicon nitride membranes, allow direct observation of the electrodes and the copolymer domain structure by transmission electron microscopy. The cylinders aligned parallel to the electric field lines for fields exceeding 30 kilovolts per centimeter, after annealing at 250°C in an inert atmosphere for 24 hours. This technique could find application in nanostructure fabrication.  相似文献   
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On the basis of synchronization of three carbon-14 (14C)-dated lacustrine sequences from Sweden with tree ring and ice core records, the absolute age of the Younger Dryas-Preboreal climatic shift was determined to be 11,450 to 11,390 +/- 80 years before the present. A 150-year-long cooling in the early Preboreal, associated with rising Delta14C values, is evident in all records and indicates an ocean ventilation change. This cooling is similar to earlier deglacial coolings, and box-model calculations suggest that they all may have been the result of increased freshwater forcing that inhibited the strength of the North Atlantic heat conveyor, although the Younger Dryas may have begun as an anomalous meltwater event.  相似文献   
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