Effect of season and temperature on mortality in amphibians due to chytridiomycosis

OBJECTIVE: To investigate the distribution and incidence of chytridiomycosis in eastern Australian frogs and to examine the effects of temperature on this disease. DESIGN: A pathological survey and a transmission experiment were conducted. PROCEDURE: Diagnostic pathology examinations were performed on free-living and captive, ill and dead amphibians collected opportunistically from eastern Australia between October 1993 and December 2000. We conducted a transmission experiment in the laboratory to investigate the effects of temperature: eight great barred frogs (Mixophyes fasciolatus) exposed to zoospores of Batrachochytrium dendrobatidis and six unexposed frogs were housed individually in each of three rooms held at 17 degrees C, 23 degrees C and 27 degrees C. RESULTS: Chytridiomycosis was the cause of death or morbidity for 133 (55.2%) of 241 free-living amphibians and for 66 (58.4%) of 113 captive amphibians. This disease occurred in 34 amphibian species, was widespread around the eastern seaboard of Australia and affected amphibians in a variety of habitats at high and low altitudes on or between the Great Dividing Range and the coast. The incidence of chytridiomycosis was higher in winter, with 53% of wild frogs from Queensland and New South Wales dying in July and August. Other diseases were much less common and were detected mostly in spring and summer. In experimental infections, lower temperatures enhanced the pathogenicity of B. dendrobatidis in M. fasciolatus. All 16 frogs exposed to B. dendrobatidis at 17 degrees C and 23 degrees C died, whereas 4 of 8 frogs exposed at 27 degrees C survived. However, the time until death for the frogs that died at 27 degrees C was shorter than at the lower temperatures. Infections in survivors were eliminated by 98 days. CONCLUSION: Chytridiomycosis is a major cause of mortality in free-living and captive amphibians in Australia and mortality rate increases at lower temperatures.     

When Ecological Information Meets High Wildlife Value Orientations: Influencing Preferences of Nearby Residents for Urban Wetlands

Preferences for landscapes are critical because they can drive landscape changes over time. The mediating role of wildlife value orientations in influencing preferences for urban wetlands through the provision of ecological information (based on insectivorous bats) was experimentally tested. Residents (N = 198) were asked about their preferences for wetlands, as depicted in 27 photographs. Half of the participants were provided with ecological information. Urban wetlands of high habitat quality for bats were preferred by both groups. There was a significant influence of ecological information on preference, although unexpectedly, this was on wetlands of low quality habitat; people who received ecological information had lower preferences for wetlands that provided lower quality habitat for bats. This influence was mediated by wildlife value orientations (wildlife rights and recreational wildlife experiences). Results suggest that preferences for landscapes can be influenced by providing information that is consistent with value orientations.     

Comparison of the selection of antimicrobial resistance in fecal Escherichia coli during enrofloxacin administration with a local drug delivery system or with intramuscular injections in a swine model

This study evaluated, for the first time, the selection of antibiotic resistance in fecal Escherichia coli, a potential reservoir of genes of resistance, during the prolonged exposure to fluoroquinolones after the implantation of a local drug delivery system (LDDS) in a swine model. Fourteen pigs were randomly assigned to group IM (5 mg/kg/day of intramuscular enrofloxacin--EFX) or LD (surgical implantation of EFX-polymethyl-methacrylate peri-femoral implants). Blood samples were collected daily for determination of plasma EFX and ciprofloxacin (CFX) concentrations. Fecal samples were collected daily to determine the E. coli counts and the susceptibility patterns of its isolates as evaluated by antibiotic disk diffusion tests. In both groups, EFX administration significantly reduced the bacterial counts after 2 days. During recolonization, the bacterial counts remained lower than baseline in group IM but not significantly, and almost reached pre-treatment levels in group LD. Susceptibility to EFX, CFX, and nalidixic acid of recolonizing E. coli in LD pigs slightly decreased but remained within the limit of "susceptible" isolates. In contrast, quinolone susceptibility of recolonizing E. coli in IM pigs dropped dramatically (P < 0.0001). In addition, intramuscular exposure to fluoroquinolones significantly decreased the susceptibility of E. coli to ampicillin and trimethoprim-sulfamethoxazole (P < 0.05). In conclusion, the use of a dosing regimen that minimized the intestinal output of fluoroquinolones also minimized the selection of resistance to several classes of antibiotics. This could represent another advantage of LDDS usage compared to long-lasting systemic administration of fluoroquinolones.     

Interactive computerized learning program exposes veterinary students to challenging international animal-health problems

This article describes a computerized case-based CD-ROM (CD) on international animal health that was developed to give veterinary students an opportunity to "virtually" work alongside veterinarians and other veterinary students as they try to solve challenging disease problems relating to tuberculosis in South African wildlife, bovine abortion in Mexico, and neurologic disease in horses in Rapa Nui, Chile. Each of the three case modules presents, in a highly interactive format, a problem or mystery that must be solved by the learner. As well as acquiring information via video clips and text about the specific health problem, learners obtain information about the different countries, animal-management practices, diagnostic methods, related disease-control issues, economic factors, and the opinions of local experts. After assimilating this information, the learner must define the problem and formulate an action plan or make a recommendation or diagnosis. The computerized program invokes three principles of adult education: active learning, learner-centered education, and experiential learning. A medium that invokes these principles is a potentially efficient learning tool and template for developing other case-based problem-solving computerized programs. The program is accessible on the World Wide Web at . A broadband Internet connection is recommended, since the modules make extensive use of embedded video and audio clips. Information on how to obtain the CD is also provided.     

Effect of water temperature manipulation on a thermal unit predictive model for Loma salmonae

Loma salmonae is an important microsporidian pathogen affecting the mariculture of Pacific salmon, Oncorhynchus tshawytscha (Walbaum). Clinical signs associated with infection arise when the parasite enters sporogony and forms xenoparasitic complexes (xenomas) within the gill. The present study tested a thermal unit (TU) model, which was devised to predict the timing of xenoma formation, under conditions in which water temperature changed during the course of infection. In vivo trials with juvenile trout showed that the model TU for xenoma onset= (days post exposure) (C above 7C) accurately predicted the onset time for xenomas when fish were moved from either 11 or 5C to 15C at various intervals after exposure. These findings suggest that the TU model may allow aquaculturists to predict disease onset. However, the model failed when fish were moved from 15 to 5C at intervals after exposure. This finding suggests that the temperature-constrained phase of the life-cycle of L. salmonae occurs early on after the spore is ingested by the fish.