Life-history trade-offs allow many animals to maintain reproductive fitness across a range of climatic conditions. When used by parasites and pathogens, these strategies may influence patterns of disease in changing climates. The chytrid fungus, Batrachochytrium dendrobatidis, is linked to global declines of amphibian populations. Short-term growth in culture is maximal at 17 degrees-25 degrees C. This has been used in an argument that global warming, which increases the time that amphibians spend at these temperatures in cloud-covered montane environments, has led to extinctions. Here we show that the amphibian chytrid responds to decreasing temperatures with trade-offs that increase fecundity as maturation rate slows and increase infectivity as growth decreases. At 17 degrees-25 degrees C, infectious zoospores encyst (settle and develop a cell wall) and develop into the zoospore-producing stage (zoosporangium) faster, while at 7 degrees-10 degrees C, greater numbers of zoospores are produced per zoosporangium; these remain infectious for a longer period of time. We modeled the population growth of B. dendrobatidis through time at various temperatures using delayed differential equations and observational data for four parameters: developmental rate of thalli, fecundity, rate of zoospore encystment, and rate of zoospore survival. From the models, it is clear that life-history trade-offs allow B. dendrobatidis to maintain a relatively high long-term growth rate at low temperatures, so that it maintains high fitness across a range of temperatures. When a seven-day cold shock is simulated, the outcome is intermediate between the two constant temperature regimes, and in culture, a sudden drop in temperature induces zoospore release. These trade-offs can be ecologically important for a variety of organisms with complex life histories, including pathogenic microorganisms. The effect of temperature on amphibian mortality will depend on the interaction between fungal growth and host immune function and will be modified by host ecology, behavior, and life history. These results demonstrate that B. dendrobatidis populations can grow at high rates across a broad range of environmental temperatures and help to explain why it is so successful in cold montane environments.

The efficacy of a number of disinfection treatments was tested on in vitro cultures of the fungus Batrachochytrium dendrobatidis, the causative agent of chytridiomycosis in amphibians. The aim was to evaluate the fungicidal effects of chemical disinfectants, sterilising ultraviolet (UV) light, heat and desiccation, using methods that were feasible for either disinfection in the field, in amphibian husbandry or in the laboratory. The chemical disinfectants tested were: sodium chloride, household bleach (active ingredient: sodium hypochlorite), potassium permanganate, formaldehyde solution, Path-X TM agricultural disinfectant (active ingredient: didecyl dimethyl ammonium chloride, DDAC), quaternary ammonium compound 128 (DDAC), Dithane, Virkon, ethanol and benzalkonium chloride. In 2 series of experiments using separate isolates of B. dendrobatidis, the fungicidal effect was evaluated for various time periods and at a range of chemical concentrations. The end point measured was death of 100% of zoospores and zoosporangia. Nearly all chemical disinfectants resulted in 100% mortality for at least one of the concentrations tested. However, concentration and time of exposure was critical for most chemicals. Exposure to 70% ethanol, 1 mg Virkon ml -1 or 1 mg benzalkonium chloride ml -1 resulted in death of all zoosporangia after 20 s. The most effective products for field use were Path-X TM and the quaternary ammonium compound 128, which can be used at dilutions containing low levels (e.g. 0.012 or 0.008%, respectively) of the active compound didecyl dimethyl ammonium chloride. Bleach, containing the active ingredient sodium hypochlorite, was effective at concentrations of 1% sodium hypochlorite and above. Cultures did not survive complete drying, which occurred after < 3 h at room temperature. B. dendrobatidis was sensitive to heating, and within 4 h at 37°C, 30 min at 47°C and 5 min at 60°C, 100% mortality occurred. UV light (at 1000 mW m -2 with a wavelength of 254 nm) was ineffective at killing B. dendrobatidis in culture. Disinfectants play a role in at least 3 situations: (1) to prevent the spread of amphibian disease in the wild by cleaning equipment that comes into contact with amphibians, such as nets and toe-clipping instruments, as well as by cleaning items that come into contact with water, such as boots; (2) in captive husbandry, as a crucial part of quarantine in cleaning equipment and enclosures before reuse, and (3) in the laboratory, to prevent contamination and to kill unwanted cultures. An ideal disinfectant would work rapidly, be safe for the human operator, have minimal impact on equipment, have a low risk of contaminating the environment, be easily available, and any residual concentration would have no effect on amphibians.Because a resistant resting spore has not been detected for Batrachochytrium dendrobatidis , this study evaluates the ability of a disinfectant to kill zoospores and zoosporangia only. MATERIALS AND METHODSThe physical techniques tested were desiccation, ultraviolet (...

Amphibian chytridiomycosis is an emerging infectious disease of amphibians thought to be moved between countries by trade in infected amphibians. The causative fungus, Batrachochytrium dendrobatidis, produces aquatic, motile zoospores; infections have been achieved in experiments by exposing amphibians to water containing zoospores. However, the ability of this fungus to survive in the environment in the absence of an amphibian host is unknown. We show that B. dendrobatidis will survive in tap water and in deionized water for 3 and 4 weeks, respectively. In lake water, infectivity was observed for 7 weeks after introduction. The knowledge that water can remain infective for up to 7 weeks is important for the formulation of disease control and quarantine strategies for the management of water that has been in contact with amphibians.

Amphibian chytridiomycosis caused by Batrachochytrium dendrobatidis has spread at an alarming rate over large distances throughout sensitive frog populations in eastern Australia, Central America and New Zealand. Infected amphibians and contaminated water are implicated in translocation, but other vectors are unknown. Through in vitro studies we show that potential means of translocation may be moist soil and bird feathers. B. dendrobatidis survived for up to 3 mo in sterile, moist river sand with no other nutrients added. B. dendrobatidis attached to and grew on sterile feathers and were able to be transported by feathers to establish new cultures in media, surviving between 1 and 3 h of drying between transfers. If these in vitro results are valid in the natural environment, the findings raise the possibilities that B. dendrobatidis may be translocated by movement of moist river sand and that birds may carry the amphibian chytrid between frog habitats. However, further studies using sand and feathers containing normal microflora are essential. KEY WORDS: Batrachochytrium dendrobatidis · Chytridiomycosis · Amphibian chytrid · Translocation · Feathers · Soil Resale or republication not permitted without written consent of the publisherDis Aquat Org 65: [181][182][183][184][185][186] 2005 the methods of dissemination of B. dendrobatidis are particularly important in understanding its life cycle and attempting to control the spread of this highly pathogenic organism. It is currently hypothesised that the fungus is spread by its own movement through water bodies, via surface water during precipitation, or by the activity of individual infected amphibians (Speare et al. 2001). It has also been postulated that the fungus may be transported by one or more vectors such as waterbirds, migratory fish, or by the introduced cane toad Bufo marinus (Laurance et al. 1997. The growth of other members of the phylum Chytridiomycota in soil also presents an important possibility for the chytrid organism to be spread via the movement of soil such as in extraction industries, in plant nursery products, or in contaminated soil on vehicles or footwear of hikers.In this study, Batrachochytrium dendrobatidis was inoculated into 2 types of sterile, moist soil in order to determine whether it could grow in moist soil in the absence of an amphibian host. The pH tolerance of this organism was also studied to determine if this were a factor that might influence survival in different soils. The growth of B. dendrobatidis on feathers, its ability to be transferred by bird feathers, and its survival after various periods of desiccation whilst attached to the feathers were studied in order to determine whether bird feathers might be a possible means of transport of the chytrid fungus between water bodies. MATERIALS AND METHODSTwo strains of Batrachochytrium dendrobatidis were obtained from the CSIRO Australian Animal Health Laboratory (AAHL) (Geelong, Victoria). Strain 98-1469/10 was isolated from a captive juvenile Limnodynastes d...