Do Frogs Get Their Kicks on Route 66? Continental U.S. Transect Reveals Spatial and Temporal Patterns of Batrachochytrium dendrobatidis Infection

The chytrid fungus Batrachochytrium dendrobatidis (Bd) has been devastating amphibians globally. Two general scenarios have been proposed for the nature and spread of this pathogen: Bd is an epidemic, spreading as a wave and wiping out individuals, populations, and species in its path; and Bd is endemic, widespread throughout many geographic regions on every continent except Antarctica. To explore these hypotheses, we conducted a transcontinental transect of United States Department of Defense (DoD) installations along U.S. Highway 66 from California to central Illinois, and continuing eastward to the Atlantic Seaboard along U.S. Interstate 64 (in sum from Marine Corps Base Camp Pendleton in California to Naval Air Station Oceana in Virginia). We addressed the following questions: 1) Does Bd occur in amphibian populations on protected DoD environments? 2) Is there a temporal pattern to the presence of Bd? 3) Is there a spatial pattern to the presence of Bd? and 4) In these limited human-traffic areas, is Bd acting as an epidemic (i.e., with evidence of recent introduction and/or die-offs due to chytridiomycosis), or as an endemic (present without clinical signs of disease)? Bd was detected on 13 of the 15 bases sampled. Samples from 30 amphibian species were collected (10% of known United States' species); half (15) tested Bd positive. There was a strong temporal (seasonal) component; in total, 78.5% of all positive samples came in the first (spring/early-summer) sampling period. There was also a strong spatial component—the eleven temperate DoD installations had higher prevalences of Bd infection (20.8%) than the four arid (<60 mm annual precipitation) bases (8.5%). These data support the conclusion that Bd is now widespread, and promote the idea that Bd can today be considered endemic across much of North America, extending from coast-to-coast, with the exception of remote pockets of naïve populations

Seasonal Pattern of Batrachochytrium dendrobatidis Infection and Mortality in Lithobates areolatus: Affirmation of Vredenburg's “10,000 Zoospore Rule”

To fully comprehend chytridiomycosis, the amphibian disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd), it is essential to understand how Bd affects amphibians throughout their remarkable range of life histories. Crawfish Frogs (Lithobates areolatus) are a typical North American pond-breeding species that forms explosive spring breeding aggregations in seasonal and semipermanent wetlands. But unlike most species, when not breeding Crawfish Frogs usually live singly—in nearly total isolation from conspecifics—and obligately in burrows dug by crayfish. Crayfish burrows penetrate the water table, and therefore offer Crawfish Frogs a second, permanent aquatic habitat when not breeding. Over the course of two years we sampled for the presence of Bd in Crawfish Frog adults. Sampling was conducted seasonally, as animals moved from post-winter emergence through breeding migrations, then back into upland burrow habitats. During our study, 53% of Crawfish Frog breeding adults tested positive for Bd in at least one sample; 27% entered breeding wetlands Bd positive; 46% exited wetlands Bd positive. Five emigrating Crawfish Frogs (12%) developed chytridiomycosis and died. In contrast, all 25 adult frogs sampled while occupying upland crayfish burrows during the summer tested Bd negative. One percent of postmetamorphic juveniles sampled were Bd positive. Zoospore equivalents/swab ranged from 0.8 to 24,436; five out of eight frogs with zoospore equivalents near or >10,000 are known to have died. In summary, Bd infection rates in Crawfish Frog populations ratchet up from near zero during the summer to over 25% following overwintering; rates then nearly double again during and just after breeding—when mortality occurs—before the infection wanes during the summer. Bd-negative postmetamorphic juveniles may not be exposed again to this pathogen until they take up residence in crayfish burrows, or until their first breeding, some years later

Une nouvelle imagerie ostéo-articulaire basse dose en position debout : le système EOS

L’association et la collaboration étroite de plusieurs disciplines (physique des rayonnements, biomécanique, radiologie et orthopédie de l’enfant) a permis la mise au point dans notre pays et le développement d’un nouvel appareil d’imagerie dénommé EOS dont les principales caractéristiques sont : (1) la réduction considérable des doses de rayons X (de 8 à 10 fois moins pour la radiologie bidimensionnelle, de 800 à 1000 fois moins pour la tomodensitométrie tridimensionnelle) grâce au détecteur gazeux inventé par Georges Charpak qui lui ont valu le prix Nobel. (2) L’étude du patient en position debout obtenant des clichés simultanés de face et de profil du sommet de la tête jusqu’à la plante des pieds. (3) La possibilité de reconstruction 3D de tous les niveaux ostéo-articulaires a été vérifiée aussi précise que celle obtenue par tomodensitométrie conventionnelle. De plus, l’examen est effectué en position fonctionnelle debout ou assise, ce qui n’était pas possible avec les appareils de tomodensitométrie actuellement tous en position couchée. La reconstruction 3D peut être obtenue dans des délais acceptables de 15 à 30 minutes pour un rachis complet. Ne faisant pas double emploi avec l’IRM, même si celle-ci évolue aussi vers la position debout, EOS permettra des études de la pathologie ostéo-articulaire jusque-là jamais réalisées (en particulier du rachis et des membres inférieurs) avec un examen d’ensemble de l’individu au lieu des segments fragmentés donnés jusqu’à présent par les moyens actuels, radiographies conventionnelles ou tomodensitométrie