Mycobacterium salmoniphilum infection in farmed Atlantic salmon, Salmo salar L

Multiple greyish‐white visceral nodules containing abundant rapidly growing and acid‐fast bacteria, subsequently identified as Mycobacterium salmoniphilum, were detected in moribund and newly dead market‐sized fish during a period of increased mortality in an Atlantic salmon, Salmo salar, farm in western Norway. Isolates cultured from diseased fish were phenotypically consistent with Mycobacterium sp. previously isolated from Atlantic salmon [MT 1890 (= NCIMB13533), MT1892, MT1900 and MT1901] in the Shetland Isles, Scotland. Partial sequences of 16S rDNA, ribosomal RNA internal transcribed spacer (ITS1), 65‐kDa heat‐shock protein (Hsp65) and β subunit of RNA polymerase (rpoB) revealed 97‐99% similarity with M. salmoniphilum type strain ATCC 13758^T. The source of infection was not confirmed. Koch’s postulates were fulfilled following experimental challenge of Atlantic salmon with field isolate NVI6598 ( FJ616988 ). Mortality was recorded in experimentally infected fish; however, the infection remained subclinical in the majority of affected fish over the 131‐day challenge period.     

Vaccination of calves with Mycobacteria bovis Bacilli Calmete Guerin (BCG) induced rapid increase in the proportion of peripheral blood γδ T cells

Changes in the proportion of peripheral blood T cell subsets after subcutaneous inoculation of cattle with Mycobacterium bovis Bacille Calmette-Guerin (BCG) were studied. Calves were injected with approximately 8 × 10⁶ BCG bacillus and blood samples collected at weekly intervals for flow-cytometric analyses to determine the proportion of CD4⁺, CD8⁺ and γδ T cells. In addition, whole blood samples were stimulated in vitro with M. bovis purified protein derivative (PPD) and the secreted IFN-γ quantified by ELISA. Results showed cellular and cytokine changes which could be categorized into three phases. The first phase occurred within the first 2 weeks after vaccination involving an increase in proportion of WC1⁺ γδ T cells and a concomitant increase in the secretion of IFN-γ. These two responses peaked at 2 weeks and waned thereafter. The second phase involved an increase in the CD4/CD8 ratio as a result of an increase in the proportion of CD4⁺ T cells between 4 and 6 weeks. The third phase involved a decrease in the CD4/CD8 ratio due to an increase in the proportion of CD8⁺ T cells between 8 and 10 weeks. Surprisingly, the IFN-γ response was associated with changes in the γδ rather than the CD4⁺ or CD8⁺ T cells, suggesting that this cytokine was secreted by γδ-T cells. These results are consistent with the reported ability of γδ T cells to act rapidly and bridging the innate and classically adaptive immune responses.     

Factors Affecting Small-Scale Farmers’ Land Allocation and Tree Density Decisions in an <Emphasis Type="Italic">Acacia decurrens</Emphasis>-Based <Emphasis Type="Italic">taungya</Emphasis> System in Fagita Lekoma District,North-Western Ethiopia

The development of woodlots as an additional source of livelihood and as a land management option for small-scale farmers is a challenging issue in the cereal-based subsistence farming systems of north-western Ethiopia. There is a need to understand why and which factors determine the decisions of small-scale farmers to grow short-rotation woodlots on their land. Data used in this study were collected from a survey of 200 randomly selected households in the region. A Tobit regression model was used to determine predictor variables for farmers’ decisions to allocate land to planting Acacia decurrens (J.C. Wendl.) Willd. and at what density trees are planted on the respective plots. The most important motivations for planting A. decurrens were income, soil fertility management, and soil and water conservation. Having a male head of household, long distance to markets and plots being on marginal land, among other factors, increased the allocation of land to A. decurrens woodlots. Having a male head of household, access to credit and plots being on marginal land, among other factors, increased tree planting density. Age had a negative effect on both allocation of land to woodlots and tree density, whereas farm size had an inverted U-shaped relationship with both decisions. These results suggest that wider expansion of A. decurrens-based plantation systems could be achieved through improving extension, credit access and road infrastructure to connect small-scale farmers to markets and finance.     

Impact of variable-rate application of nitrogen on yield and profit: a case study from South Africa

The response of maize (Zea mays) to banded variable-rate nitrogen (N) application over a period of 3 years (2002/3–2004/5) is analyzed. The experimental design alternated variable-rate (VR) and single-rate (SR) applications of N. The yield monitor data were spatially autocorrelated and therefore were analyzed with spatial regression methods. The baseline spatial regression model defined in this study showed that the VR treatment, treatment by year and treatment by management zone were statistically significant. Sensitivity tests were applied; the first showed that VR treatment had a yield advantage when soil depth was greater than the field average of 174 cm. The second test showed that the VR N rates applied were close to those that would maximize profit. Partial budgeting indicates that benefits from VR vary from year to year, but in this test VR was slightly more profitable than uniform rate application. Economic sensitivity testing indicates that farm size and the price of maize are the key factors in the profitability of VR N.     

Influence of elevated CO2 and mycorrhizae on nitrogen acquisition: contrasting responses in Pinus taeda and Liquidambar styraciflua

An understanding of root system capacity to acquire nitrogen (N) is critical in assessing the long-term growth impact of rising atmospheric CO2 concentration ([CO2]) on trees and forest ecosystems. We examined the effects of mycorrhizal inoculation and elevated [CO2] on root ammonium (NH4+) and nitrate (NO3-) uptake capacity in sweetgum (Liquidambar styraciflua L.) and loblolly pine (Pinus taeda L.). Mycorrhizal treatments included inoculation of seedlings with the arbuscular mycorrhizal (AM) fungus Glomus intraradices Schenck & Smith in sweetgum and the ectomycorrhizal (EM) fungus Laccaria bicolor (Maire) Orton in loblolly pine. These plants were then equally divided between ambient and elevated [CO2] treatments. After 6 months of treatment, root systems of both species exhibited a greater uptake capacity for NH4+ than for NO3-. In both species, mycorrhizal inoculation significantly increased uptake capacity for NO3-, but not for NH4+. In sweetgum, the mycorrhizal effect on NO3- and NH4+ uptake capacity depended on growth [C02]. Similarly, in loblolly pine, the mycorrhizal effect on NO3- uptake capacity depended on growth [CO2], but the effect on NH4+ uptake capacity did not. Mycorrhizal inoculation significantly enhanced root nitrate reductase activity (NRA) in both species, but elevated [CO2] increased root NRA only in sweetgum. Leaf NRA in sweetgum did not change significantly with mycorrhizal inoculation, but increased in response to [CO2]. Leaf NRA in loblolly pine was unaffected by either treatment. The results indicate that the mycorrhizal effect on specific root N uptake in these species depends on both the form of inorganic N and the mycorrhizal type. However, our data show that in addressing N status of plants under high [CO2], reliable prediction is possible only when information about other root system adjustments (e.g., biomass allocation to fine roots) is simultaneously considered.     

Diversity of Mannheimia haemolytica and Pasteurella trehalosi Serotypes from Apparently Healthy Sheep and Abattoir Specimens in the Highlands of Wollo,North East Ethiopia

The prevalence and serotypic diversity of Mannheimia [Pasteurella] haemolytica and Pasteurella trehalosi from nasal swabs, sera and abattoir specimens from sheep in the highlands of Wollo, North East Ethiopia was investigated. Prevalence rates of 83% and 75% of these microorganisms were found in the serum samples and nasal swabs, respectively, from apparently healthy sheep. In a local abattoir, 205 lungs were investigated, 34% of which showed pneumonia, from which samples were collected from 51 lungs and the same number of corresponding tonsils. Mannheimia and Pasteurella species were isolated from 59% of these pneumonic lungs and 69% of the respective tonsils. M. haemolytica serotypes accounted for 41 (59%) and P. trehalosi for 11 (32%) of the isolates from the abattoir specimens. The majority (67%) of isolates from nasal swabs were P. trehalosi, M. haemolytica being isolated f rom 4 (13%) of the swabs. M. glucosida was isolated only from the tonsils. The predominant serotypes of the isolates from both the nasal swabs and the abattoir specimens were M. haemolytica A1 (17%) and P. trehalosi T4 (16%) and T3 (13%). P. trehalosi T15 was less commonly encountered, while M. haemolytica A9 and A13 were not isolated. Studies on sera from 100 sheep indicated that antibodies against M. haemolytica serotype A1 (14%) were most common, followed by A5 and A8 (each 10%) and A9 and P. trehalosi T3 (each 9%) and T4 (8%). Antibodies against M. glucosida or serotype A11 occurred in 2% of the sera. Multiple serotypes were common in all types of samples. The importance of including in vaccines the most prevalent serotypes involved in the pneumonia of sheep in the area is discussed.     

Processes of environmental degradation and opportunities for rehabilitation in Adwa,Northern Ethiopia

There are only a few studies of land cover-land use changes which provide an integrated assessment of the biophysical and societal causes and consequences of environmental degradation in Ethiopia. Our objectives were to determine the status of the environmental degradation, analyse and evaluate the relationships among vegetation, geomorphological and socio-economic factors contributing to environmental degradation, and propose opportunities for rehabilitation of these natural resources. Field and other environmental data in northern Ethiopia and those acquired by remote sensing techniques were used to accomplish these objectives. These were integrated with socio-economic data obtained from official sources using a Geographic Information System (GIS).Spatial information such as the percent of land cover-land use types and geomorphological categories, and the percent of each land cover-land use type in the geomorphological categories were calculated using Geographic Information System (GIS). The three most dominant features of the geomorphological categories (93.0%) are scarps and denuded rock slopes, erosion surfaces and badlands, while the three most dominant features in the land cover-land use types (71.3%) are croplands, open woodlands and bushlands. Badlands account for 38.7% of the geomorphological units and 41.8% of the croplands currently occur on badlands. Simple and partial correlation analyses were applied to explore the extent of the interaction between the anthropogenic and the natural system. The anthropogenic system is influenced by elevation, which is positively correlated with human population and livestock densities and area of croplands. The natural system finds its place only on steep slopes as shown by the positive correlation between woodland,slope, high potential erosion, scarps and denudational rock slopes. The study indicates that agriculture in the study area is in a critical environmental situation. A change of paradigm in land-use and development is needed to encourage participation of the landowners and users in the efforts to conserve the vegetation and the soil. This study provides sound options that could be used to rehabilitate the vegetation directly and to alleviate the current pressure on the land and improve human welfare indirectly. Matching the human and livestock densities with the carrying capacity of the land through recruitment of the surplus labour force for a modern economy, resettlement,off-farm employment and intensification of agriculture are t he long and short-term actions that may contribute to the rehabilitation of the degraded areas. This revised version was published online in July 2006 with corrections to the Cover Date.     

Participatory investigation of Contagious Caprine Pleuropneumonia (CCPP) in goats in the Hammer and Benna-Tsemay districts of southern Ethiopia

The study was conducted in two selected districts of Southern Omo zones of Ethiopia, namely Hammer and Benna-Tsemay, during November 2004 and May 2005 to determine the status of contagious caprine pleuropneumonia (CCPP). Participatory disease investigation was conducted in the goat flocks owned by pastoralists of the districts. Participatory methods such as proportionate piling and matrix scoring of diseases were used to characterise major diseases of goats. Clinical and post-mortem examinations and isolation of the causative agent of CCPP were done. Serological tests were conducted using CFT. CCPP (locally termed Sompo) ranked as the first important disease of goats in the study area. Local perception of causes and signs of CCPP were described. Matrix scoring between groups revealed that disease signs and causes showed weak, moderate and good agreement by Kendall’s coefficient concordance (W = 0.21–0.99). The overall sero-prevalence of CCPP was 15.5%. The causative agent was isolated from sick animals in the lab. The characteristic clinical signs, gross lesions, bacteriological isolation of the causative agent supported by participatory epidemiological disease investigation revealed that CCPP is a major disease of goats in the study districts. Participatory epidemiology using indigenous knowledge could efficiently be used to generate sufficient information with minimum cost, local materials and within reasonably short period of time, assisting the designing of feasible disease control programme in developing countries.     

Evaluation of Drought Tolerance in Tef [Eragrostis Tef (Zucc.) Trotter] Genotypes Using Drought Tolerance Indices

Journal of Crop Science and Biotechnology - A field experiment was conducted to identify drought tolerant, high yielding and stable tef genotypes using drought tolerance indices. Sixty-four tef...     

Immunohistochemical and Taqman real-time PCR detection of mycobacterial infections in fish

Real‐time PCR and immunohistochemistry (IHC) assays were developed to detect fish mycobacterial infections at the genus level, based on the RNA polymerase β subunit (rpoB) gene and polyclonal anti‐Mycobacterium rabbit serum, respectively. The PCR assay positively identified a number of pathogenic mycobacteria including Mycobacterium abscessus, M. avium ssp. avium, M. bohemicum, M. chelonae ssp. chelonae, M. farcinogenes, M. flavescens, M. fortuitum ssp. fortuitum, M. gastri, M. gordonae, M. immunogenicum, M. malmoense, M. marinum, M. montefiorense, M. phlei, M. phocaicum, M. pseudoshottsii, M. salmoniphilum, M. senegalense, M. shottsii, M. smegmatis, M. szulgi and M. wolinskyi. A detection limit equivalent to 10² cfu g^?1 was registered for M. salmoniphilum‐infected fish tissue. The IHC precisely localized both free and intracellular mycobacteria in tissues and detected mycobacterial infections down to 10² cfu g^?1 tissue. Both assays were found to be more sensitive than Ziehl–Neelsen (ZN) staining, where the detection limit was below 8 × 10³ cfu g^?1 tissue. Although specificity testing of the real‐time PCR against a panel of non‐Mycobacterium spp. revealed a degree of cross‐reaction against pure DNA extracted from Nocardia seriolae and Rhodococcus erythropolis, no cross‐reactions were identified (by either real‐time PCR or IHC) on testing of formalin‐fixed paraffin‐embedded (FFPE) tissues confirmed to be infected with these bacteria. The broad applicability of both assays was confirmed by analysis of FFPE tissues from a range of fish species infected with diverse Mycobacterium spp. The results indicate that both assays, alone or in combination, constitute sensitive tools for initial, rapid diagnosis of mycobacteriosis in fish. This should in turn allow rapid application of more specific studies, i.e. culture based, to identify the specific Mycobacterium sp. involved.