BSE in the Netherlands: an update

Up to 2006, there have been 82 cases of BSE in cattle born in the Netherlands. This article reviews the current situation regarding BSE in the Netherlands and summarizes the clinical symptoms of the disease. Data from the Netherlands show that a passive surveillance system, by which farmers and veterinarians have to report suspect clinical cases, has a low sensitivity. The epidemiology of, and risk factors for, BSE are discussed. All the Dutch cases of BSE can be attributed to cross-contamination of feed with meat-and-bone meal. On the basis of information about the epidemic and the cases reported to date, it is anticipated that the number of cases of BSE will continue to decline in the Netherlands and Europe. The European Commission has presented a road map that describes how the European BSE policy can be changed in the short and long term if the current favourable trend in BSE cases continues. It is time for a new phase in the management of BSE but with continued protection of the public's health and eradication of BSE.     

In vitro markers for virulence in Yersinia ruckeri

In this study, different traits that have been associated with bacterial virulence were studied in Yersinia ruckeri. Two isolates that had been shown to cause disease and mortality in experimentally infected rainbow trout were compared with five avirulent isolates. Both virulent isolates showed high adhesion to gill and intestinal mucus of rainbow trout, whereas the majority of non‐virulent strains demonstrated significantly lower adhesion. A decrease in adherence capability following bacterial treatment with sodium metaperiodate and proteolytic enzymes suggested the involvement of carbohydrates and proteins. All strains were able to adhere to and invade chinook salmon embryo cell line (CHSE‐214), fathead minnow epithelial cell line (FHM) and rainbow trout liver cell line (R1). One non‐virulent strain was highly adhesive and invasive in the three cell lines, whereas the virulent strains showed moderate adhesive and invasive capacity. The internalization of several isolates was inhibited by colchicine and cytochalasin‐D, suggesting that microtubules and microfilaments play a role. For all strains, intracellular survival assays showed a decrease of viable bacteria in the cells 6 h after inoculation, suggesting that Y. ruckeri is not able to multiply or survive inside cultured cells. Analysis of the susceptibility to the bactericidal effect of rainbow trout serum demonstrated that virulent Y. ruckeri strains were serum resistant, whereas non‐virulent strains were generally serum sensitive.     

Quelques aspects de la chimie de l'acide ascorbique

Résumé D'après les résultats obtenus in vivo et in vitro concernant l'acide ascorbique, nous essayons d'éclaircir son rôle depuis sa génèse à sa répartition dans les végétaux. L'acide ascorbique est simple d'après sa structure et son action biologique est considérable. In vivo: l'acide ascorbique atteint son taux maximum dans les organes végétaux dans les phases déterminées de chaque période de végétation, mais les valeurs numériques de ce maximum dépendent des conditions écologiques de la période de végétation. La composition chimique des matières non azotées de ces organes est formée, dans la phase initiale de leur croissance et de leur développement, presqu'entièrement des combinaisons labiles comme ène-diols et matières fortement réductrices, et dans la phase finale des saccharides, de cellulose, des pentosanes etc. La formation la plus intense des combinaisons stables se fait dans les phases quand les fruits atteignent leur poids maximum au moment où la matière organique remplace l'eau.In vitro: le pH des solutions aqueuses et tamponnées de l'acide ascorbique et de son produit d'oxydation (l'acide déhydroascorbique) est un des facteurs qui déterminent sa propriété chimique et physique. Ainsi la solution équimoléculaire de ces deux acides, aqueuse et tamponnée, de valeurs différentes du pH se comporte de manière qu'on pourrait supposer, qu'il s'agit de l'interaction entre eux. Ensuite les valeurs du pouvoir rotatoire, calculées et trouvées pour les solutions aqueuses et tamponnées du mélange de ces acides, sont différentes, en dépendance du pH. Le pH du suc des végétaux pourrait être, donc, un des facteurs conditionnant la transformation, la dégradation et l'isomérisation de l'acide ascorbique et de l'acide déhydroascorbique in vivo par les voies différentes.La question se pose, si ce comportement de l'acide ascorbique mène à la synthèse d'autres composés nécessaires pour le développement de la plante.

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Summary On the basis of the results obtained in vivo and in vitro concerning ascorbic acid, we are attempting to clarify its role from its genesis to its distribution in the plants. Ascorbic acid is simple in its structure, and its biological action is considerable.In vivo: the maximum content of ascorbic acid occurs in plant organs in determined phases of each vegetation period, but the numerical values of these maxima are dependent on the ecological conditions of the vegetation period. The chemical composition of the non-nitrogen components of these organs is formed, in the initial phases of their growth and development, almost entirely of labile compounds, such as ene-diols and strongly reducing substances, and in the final phases of saccharides, of cellulose, of pentosans, etc. The most intensive formation of these stable combinations is effected during the phases when the fruits attain their maximum weight at the moment when water is replaced by organic substances. In vitro: the pH of aqueous and buffered solutions of ascorbic acid and of the product of its oxydation (dehydroascorbic acid) is one of the factors that determine its chemical and physical properties. Thus the equimolecular solution, aqueous and buffered, of different pH values of these two acids, behaves as one would suppose when it comes to an interaction between them. Furthermore the rotatory power values, calculated and found for aqueous and buffered solutions of these acids, differ, depending on the pH. The pH of the vegetable sap could then be one of the factors conditioning the transformation, the degradation, and the isomerization in vivo of ascorbic acid and of dehydroascorbic acid by different pathways.The question remains, whether or not this behaviour of ascorbic acid leads to the synthesis of other compounds that are necessary to the development of the plant.

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Zusammenfassung Auf Grund der Ergebnisse von Versuchen in vivo und in vitro, betreffend Askorbin-Säure, probieren wir ihre Rolle zu erklären, vom Anfang ihrer Entstehung bis zu ihrer Verteilung in den Pflanzen. Die Askorbin-Säure ist einfach, ihrer Struktur nach, und ihre biologische Wirkung ist bedeutend.In vivo: Die Maxima der Ascorbinsäure-Gehalte treten in pflanzlichen Organen in bestimmten Phasen jeder Vegetationsperiode auf. Die absolute Höhe ist jedoch von den ökologischen Bedingungen der Wachstumsperiode abhängig. Die stickstofffreien Substanzen dieser Organe setzen sich in der Anfangsphase des Wachstums und während der Entwicklung fast ausschließich aus labilen Verbindungen, wie Endiolen und stark reduzierenden Verbindungen, zusammen und in der Endphase aus Sacchariden, Cellulose, Pentosanen usw. Die stärkste Bildung dieser stabilen Verbindungen erfolgt in der Phase, in der die Früchte bei Ersatz des Wassers durch organische Substanzen ihr höchstes Gewicht erreichen.In vitro: Der pH-Wert der wäßrigen und gepufferten Lösungen von Ascorbinsäure und ihres Oxydationsproduktes — Dehydroascorbinsäure — ist einer der Faktoren, der die chemische Reaktionsfähigkeit bestimmt. So verhält sich die äquimolare wäßrige und gepufferte Lösung dieser beiden Säuren bei verschiedenen pH-Werten so, daß man eine gegenseitige Beeinflussung annehmen kann. Auch die optische Drehung der wäßrigen und gepufferten Lösungen von Mischungen dieser Säuren variiert in Abhängigkeit von pH-Wert. Der pH-Wert des Pflanzensaftes könnte somit einer der die Umwandlung, den Abbau und die Isomerisierung der Ascorbinsäure und der Dehydroascorbinsäure in vivo bedingenden Faktoren sein.

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Gamma-lactone de l'acide 2-céto L(+)-gulonique. Vitamine C.     

Limnological changes in a sub‐tropical shallow hypertrophic lake during its restoration: two years of a whole‐lake experiment

1. Lake Rodó is a turbid system, a condition attributed to algal biomass. The proximal source of the eutrophication was stormwater discharges from an ill‐defined urban area. This paper describes an attempt to restore the water quality of Lake Rodó, the first time this has been done in Uruguay. In spring 1996 it was drained, sediments were removed and stream inputs were diverted. Groundwater was used to re‐fill the lake. Due to its high nutrient concentration a re‐circulation system was designed, pumping water from associated pools covered with free‐floating plants. 2. After the lake was refilled, the system was characterized by oxygen saturation or over‐saturation, neutral to basic pH, and high phosphorus, nitrogen and silicate concentrations. Ratios of total nitrogen (TN):total phosphorus (TP) and chlorophyll a (Chl a):TP indicated that phosphorus was the primary limiting nutrient during the period of groundwater supply. Once groundwater pumping had ceased, there was a decrease in TN:TP and Chl a:TP ratios, suggesting N‐limiting conditions prevailed in some periods. 3. Before restoration, the phytoplankton community was dominated year‐round by Planktothrix agardhii; since restoration the community has been more diverse. This change has favoured grazing by mesozooplankton, and the onset of clear‐water phases in spring. 4. Abundant populations of small omnivorous fish maintained a high predation pressure on zooplankton, restricting the abundance of large‐bodied herbivores, which, in turn, allowed an increase in phytoplanton biomass and a decrease in water transparency. Based on this observation, together with the phosphorus concentration and the low abundance of filamentous cyanobacteria compared with previous studies, we suggest that top‐down control has played a key role in increasing transparency in Lake Rodó. 5. A nutrient reduction programme, by the mechanical harvest of floating plants, and a removal of small omnivorous fishes and stocking strictly with piscivores, could be key factors in the achievement of a stable clear‐water phase. However, if blooms of Microcystis or other similar genera occur in summer, additional measures (e.g. reduction of the hydraulic residence time) will be needed to improve water transparency. Copyright © 2001 John Wiley & Sons, Ltd.     

THE EFFECT OF NITROGEN APPLICATION AND AUTUMN MANAGEMENT ON AUTUMN GROWTH, WINTER 'BURN' AND SPRING GROWTH OF LOLIUM PERENNE L. AT ABERYSTWYTH, EDINBURGH AND CAMBRIDGE.

A trial was carried out to find management practices which would permit the best discrimination for winter performance of erennial ryegrass cultivars. Due to the mild winter experienced only a few of the plants were killed outright. The cultivars were therefore assessed for percentage of green herbage and for spring growth. There were four sites: an upland and lowland site at Aberystwyth and one site each at Edinburgh and Cambridge. At all sites two N rates (totals of 125 or 550 kg/ha in the first year after sowing) and 5 autumn cutting treatments were used to give differences in the amounts of herbage remaining at the onset of winter. The last dates of defoliation in the autumn were: C₁ end of August; C₂ end of September; C₃ end of October; C₄ mid-November; C₅ was cut on all these dates. Four cultivars (Grasslands Ruanui, S321, Premo and Argo) which differed in their autumn growth potential, frost susceptibility and degree of winter dormancy were grown. The autumn yield of S321 was, in general, higher than that of the other cultivars but there were interactions with N, management and location. The data on percentage of herbage remaining green in February illustrated differences due to the siting of the trial. In the conditions prevailing the two Aberystwyth sites facilitated greater discrimination between cultivars than those at Edinburgh and Cambridge. In three of the four sites the management which produced most winter ‘burn’(including both that due to natural senescence and that due to winter damage) involved accumulation of herbage in the autumn but there were considerable sites × managements interactions. For example at Cambridge management produced no significant effect whereas at the Aberystwyth lowland site frequent defoliation in the autumn had more effect than allowing herbage to remain uncut after the end of August. High N significantly decreased the percentage of green herbage only at the two Aberystwyth sites. Over five-fold differences in spring yield were obtained, the heaviest yields being recorded at Edinburgh and Cambridge. However, there were large interactions between environments and cultivars; for example the higher N rate reduced spring yield at Aberystwyth but increased spring yield at Edinburgh and Cambridge. Premo and S321 had similar yields in spring at the Aberystwyth lowland and Cambridge sites but Premo was higher yielding than S321 at the Aberystwyth upland site and at Edinburgh. The large environmental effects and their interactions with cultivars illustrate the difficulties of cultivar assessment and the dangers inherent in national recommendations for grass cultivars.