Possible modes of dissemination of the amphibian chytrid Batrachochytrium dendrobatidis in the environment

Abstract

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...

Condition-dependent reproductive effort in frogs infected by a widespread pathogen

“…However, this seems unlikely. The effects of rates of physical contact between frogs on rates of transmission of B. dendrobatidis are not known, but frogs can also become infected by contact with water or substrates, both of which can harbour infectious B. dendrobatidis zoospores [48,49]. In addition, zoospores can be carried and released into the environment by non-amphibian hosts, including nematodes and crayfish [50,51], and non-amphibian reservoirs, including reptiles and waterfowl [52,53].…”

Emerging infectious disease and the loss of biodiversity in a Neotropical amphibian community

“…As prevalence increases within the amphibian community, diseased frogs shed zoospores into the environment or directly pass them to other amphibians by contact. In the laboratory, B. dendrobatidis zoospores remain viable for at least 3 mo in sterile sand or bird feathers (21), and infected frogs and salamanders can carry an infection 24-220 days before dying, with animals at cooler temperatures shedding zoospores over a longer period (refs. 22, 23, and V. Miera, unpublished data).…”

Chytrid fungus Batrachochytrium dendrobatidis has nonamphibian hosts and releases chemicals that cause pathology in the absence of infection

“…Recently, it was reported that B. dendrobatidis can be carried on algae (12), terrestrial reptiles (19), waterfowl (20), and nematodes (21), but there is currently no evidence that these carriers actually supported pathogen growth or transmission, which would be necessary to explain the long-term persistence of B. dendrobatidis in the absence of amphibians. Other studies have grown B. dendrobatidis on boiled snake skin (11,22), sterilized bird feathers (23), and toe scales from waterfowl (20), but none of these studies demonstrated B. dendrobatidis growth on live hosts with functioning immune systems. Consequently, we lack studies that demonstrate B. dendrobatidis growth on living, nonamphibian hosts, transmission of B. dendrobatidis from these hosts to amphibians, and links between nonamphibian hosts and B. dendrobatidis prevalence in the field.…”