Ecological drivers of African swine fever virus persistence in wild boar populations: Insight for control

Environmental sources of infection can play a primary role in shaping epidemiological dynamics; however, the relative impact of environmental transmission on host‐pathogen systems is rarely estimated. We developed and fit a spatially explicit model of African swine fever virus (ASFV) in wild boar to estimate what proportion of carcass‐based transmission is contributing to the low‐level persistence of ASFV in Eastern European wild boar. Our model was developed based on ecological insight and data from field studies of ASFV and wild boar in Eastern Poland. We predicted that carcass‐based transmission would play a substantial role in persistence, especially in low‐density host populations where contact rates are low. By fitting the model to outbreak data using approximate Bayesian computation, we inferred that between 53% and 66% of transmission events were carcass‐based that is, transmitted through contact of a live host with a contaminated carcass. Model fitting and sensitivity analyses showed that the frequency of carcass‐based transmission increased with decreasing host density, suggesting that management policies should emphasize the removal of carcasses and consider how reductions in host densities may drive carcass‐based transmission. Sensitivity analyses also demonstrated that carcass‐based transmission is necessary for the autonomous persistence of ASFV under realistic parameters. Autonomous persistence through direct transmission alone required high host densities; otherwise re‐introduction of virus periodically was required for persistence when direct transmission probabilities were moderately high. We quantify the relative role of different persistence mechanisms for a low‐prevalence disease using readily collected ecological data and viral surveillance data. Understanding how the frequency of different transmission mechanisms vary across host densities can help identify optimal management strategies across changing ecological conditions.     

Dos and don'ts of testing the geographic mosaic theory of coevolution

The geographic mosaic theory of coevolution is stimulating much new research on interspecific interactions. We provide a guide to the fundamental components of the theory, its processes and main predictions. Our primary objectives are to clarify misconceptions regarding the geographic mosaic theory of coevolution and to describe how empiricists can test the theory rigorously. In particular, we explain why confirming the three main predicted empirical patterns (spatial variation in traits mediating interactions among species, trait mismatching among interacting species and few species-level coevolved traits) does not provide unequivocal support for the theory. We suggest that strong empirical tests of the geographic mosaic theory of coevolution should focus on its underlying processes: coevolutionary hot and cold spots, selection mosaics and trait remixing. We describe these processes and discuss potential ways each can be tested.     

Antibody Persistence and Booster Responses to Split-Virion H5N1 Avian Influenza Vaccine in Young and Elderly Adults

Avian influenza continues to circulate and remains a global health threat not least because of the associated high mortality. In this study antibody persistence, booster vaccine response and cross-clade immune response between two influenza A(H5N1) vaccines were compared. Participants aged over 18-years who had previously been immunized with a clade 1, A/Vietnam vaccine were re-immunized at 6-months with 7.5 μg of the homologous strain or at 22-months with a clade 2, alum-adjuvanted, A/Indonesia vaccine. Blood sampled at 6, 15 and 22-months after the primary course was used to assess antibody persistence. Antibody concentrations 6-months after primary immunisation with either A/Vietnam vaccine 30 μg alum-adjuvanted vaccine or 7.5 μg dose vaccine were lower than 21-days after the primary course and waned further with time. Re-immunization with the clade 2, 30 μg alum-adjuvanted vaccine confirmed cross-clade reactogenicity. Antibody cross-reactivity between A(H5N1) clades suggests that in principle a prime-boost vaccination strategy may provide both early protection at the start of a pandemic and improved antibody responses to specific vaccination once available.Trial Registration: ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT00415129","term_id":"NCT00415129"}}NCT00415129     

Functional roles for the cytoplasmic domain of the type III transforming growth factor beta receptor in regulating transforming growth factor beta signaling

Transforming growth factor beta (TGF-beta) signals through three high affinity cell surface receptors, TGF-beta type I, type II, and type III receptors. The type III receptor, also known as betaglycan, binds to the type II receptor and is thought to act solely by "presenting" the TGF-beta ligand to the type II receptor. The short cytoplasmic domain of the type III receptor is thought to have no role in TGF-beta signaling because deletion of this domain has no effect on association with the type II receptor, or with the presentation role of the type III receptor. Here we demonstrate that the cytoplasmic domains of the type III and type II receptors interact specifically in a manner dependent on the kinase activity of the type II receptor and the ability of the type II receptor to autophosphorylate. This interaction results in the phosphorylation of the cytoplasmic domain of the type III receptor by the type II receptor. The type III receptor with the cytoplasmic domain deleted is able to bind TGF-beta, to bind the type II receptor, and to enhance TGF-beta binding to the type II receptor but is unable to enhance TGF-beta2 signaling, determining that the cytoplasmic domain is essential for some functions of the type III receptor. The type III receptor functions by selectively binding the autophosphorylated type II receptor via its cytoplasmic domain, thus promoting the preferential formation of a complex between the autophosphorylated type II receptor and the type I receptor and then dissociating from this active signaling complex. These studies, for the first time, elucidate important functional roles of the cytoplasmic domain of the type III receptor and demonstrate that these roles are essential for regulating TGF-beta signaling.     

Essential fatty acid interconversion during gestation in the rat

The synthesis of arachidonic acid has been investigated in fetal and pregnant rat liver microsomes in the course of the gestation. The delta 5-desaturase activity decreased 2-3 times in rat liver between the 19th and 22nd day of the pregnancy. During this period the delta 5-desaturate activity increased 3-fold in the fetal liver, exceeding the activity of the maternal liver. In contrast, the activity of the fetal delta 6-desaturase was in the same range as in pregnant rat liver and the liver of control animals and did not change between these two stages of the gestation. The elongation rate of linoleic acid in fetal liver was 2-3 times lower than in maternal liver but this increased during the pregnancy. The fatty acid activate rate was always higher than the activity of the desaturases. At the 19th day, the activity of the delta 5-desaturase was apparently the rate limiting step of arachidonic acid synthesis in fetal liver. We did not find any delta 5- and delta 6-desaturase activities or linoleic acid elongation in the placenta microsomes.     

Le comportement parasitaire de Sclerotinia tuberosa (hedw.) Fuckel sur Anemone nemorosa L. Etude en microscopie photonique et electronique a balayage

Résumé Des rhizomes d'Anemone nemorosa infectés par Sclerotinia tuberosa ont été trouvés dans le sol. Ils ont été étudiés macroscopiquement, en microscopie photonique et en microscopie électronique à balayage. Des infections artificielles ont été réalisées in vitro. Un manchon mycélien entoure le rhizome, et des coussinets d'infection se forment au contact de la cuticule où ils émettent des filaments d'infection qui traversent les couches cuticulaires successivement sécrétées par l'hôte. La colonisation des tissus du rhizome se fait par voie intracellulaire, des appressoria simples servant à franchir les parois cellulaires, mais aussi par voie intercellulaire si l'infection débute au niveau d'une blessure du rhizome. Les mécanismes observés sont en accord avec les préférences nutritionnelles du champignon en culture pure.

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Rhizomes of Anemone nemorosa infected by Sclerotinia tuberosa have been found in soil. They have been studied macroscopically and by means of light and scanning electron microscopy. In addition artificial infections have been produced in vitro. Fungal hyphae coat the rhizome with a mycelial muff. Infection cushions develop near the cuticle, and they produce infection threads which penetrate through it. The colonization of the host plant tissues goes on either by intracellularly — the hyphae then go from cell to cell, perforating the cell walls by mean of simple appressoria — or by intercellularly — especially when the infection is initiated by a wound in the rhizome. The infection mechanisms observed here fit well with the nutritional requirements of the fungus in pure culture.

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Avec la collaboration technique de D. Bernillon     

No down-regulation of leaf photosynthesis in mature forest trees after three years of exposure to elevated CO2

The photosynthetic responses of six species of mature forest trees to long-term exposure to elevated CO2 (ca. 530 ppm) were determined at the Swiss Canopy Crane (SCC) site near Basel, Switzerland. In the third year of growth in elevated CO2, using web-FACE technology, net photosynthesis (As) in fully sunlit, upper canopy foliage was stimulated by ca. 40% compared to ambient controls. This enhancement did not differ from the instantaneous increase in As found in ambient-grown leaves that were temporarily measured at elevated CO2. A complete lack of down-regulation of photosynthesis was found in all species and in both the early and the late growing season. Neither was leaf nitrogen content significantly affected by long-term exposure to elevated CO2. Our results document a persistent enhancement in leaf level photosynthesis in response to elevated CO2 in mature forest trees over a period of three years. Circumstantial evidence suggests that the additional assimilates feed into large sinks other than stem and shoot growth.     

Critical thermal maxima of diploid and triploid brook charr, Salvelinus fontinalis

The purpose of this experiment was to determine whether diploid and triploid brook charr, Salvelinus fontinalis, differ in their critical thermal maxima (CTM). Two age classes were tested (underyearlings, having average weight of 25 g, and yearlings, having average weight of 668 g) at two rates of temperature increase (2° C h^-1 and 15° C h^-1). No effect of ploidy on CTM was found. Fish exposed to the faster rate of temperature increase had higher CTM values than those exposed to the slower rate (underyearlings: 29.5 ± 0.1° C versus 29.1 ± 0.1° C in one trial and 29.8 ± 0.1° C versus 28.3 ± 0.1° C in a second trial; yearlings: 29.3 ± 0.1° C versus 27.7 ± 0.1° C in two trials, p < 0.001 in all cases). Underyearlings had higher CTM values than yearlings (29.2 ± 0.1° C versus 28.5 ± 0.1° C, p < 0.05). Female yearlings, which were immature, had higher CTM values than males, which had previously matured as one-year-olds (28.8 ± 0.1° C versus 28.3 ± 0.1° C, p < 0.001).     

Arachidonate cannot be released directly from diacyl-sn-glycero-3-phosphocholine in thrombin-stimulated platelets.

The origin of the arachidonate released from platelets on stimulation with thrombin was investigated by comparing the specific activities of released arachidonate and of arachidonoyl-containing phospholipids using rat platelets prelabelled with arachidonate. Quantification of the released arachidonate was determined in the presence of BW 755 C, a dual cyclo-oxygenase/lipoxygenase inhibitor, which was found not to modify the arachidonate mobilization between the platelet phospholipids. The phospholipid molecular species were analysed by h.p.l.c. of diradylglycerol benzoate derivatives of diacyl, alkylacyl and alkenylacyl classes. The labelled/unlabelled arachidonate ratio varied greatly in the phospholipids depending on whether an ether or acyl bond was present in sn-1 position of the glycerol, on the length and degree of unsaturation of this fatty chain and on the polar head group. Between 15 s and 5 min of stimulation by thrombin, the released arachidonate kept a constant specific activity which was considerably lower than the specific activity of diacyl-GPC. The specific activity of the released arachidonate was intermediate between the specific activities of the 16:0-20:4 and 18:0-20:4 species of diacyl-GPI and diacyl-GPE, and corresponded to the mean specific activity of alkylacyl-GPC. The data indicate that the released arachidonate cannot come directly from diacyl-GPC, and that two phospholipids in particular can act as direct precursors of the released arachidonate. These are (1) the alkylacyl-GPC and (2) the diacyl-GPE whose hydrolysis would induce an arachidonate transfer from diacyl-GPC.