Mitigating amphibian disease: strategies to maintain wild populations and control chytridiomycosis

Abstract

BackgroundRescuing amphibian diversity is an achievable conservation challenge. Disease mitigation is one essential component of population management. Here we assess existing disease mitigation strategies, some in early experimental stages, which focus on the globally emerging chytrid fungus Batrachochytrium dendrobatidis. We discuss the precedent for each strategy in systems ranging from agriculture to human medicine, and the outlook for each strategy in terms of research needs and long-term potential.ResultsWe find that the effects of exposure to Batrachochytrium dendrobatidis occur on a spectrum from transient commensal to lethal pathogen. Management priorities are divided between (1) halting pathogen spread and developing survival assurance colonies, and (2) prophylactic or remedial disease treatment. Epidemiological models of chytridiomycosis suggest that mitigation strategies can control disease without eliminating the pathogen. Ecological ethics guide wildlife disease research, but several ethical questions remain for managing disease in the field.ConclusionsBecause sustainable conservation of amphibians in nature is dependent on long-term population persistence and co-evolution with potentially lethal pathogens, we suggest that disease mitigation not focus exclusively on the elimination or containment of the pathogen, or on the captive breeding of amphibian hosts. Rather, successful disease mitigation must be context specific with epidemiologically informed strategies to manage already infected populations by decreasing pathogenicity and host susceptibility. We propose population level treatments based on three steps: first, identify mechanisms of disease suppression; second, parameterize epizootiological models of disease and population dynamics for testing under semi-natural conditions; and third, begin a process of adaptive management in field trials with natural populations.

Mitigating amphibian chytridiomycoses in nature

“…However, without a solid understanding of host-pathogen dynamics and the biology of the host and pathogen in the landscape, translocations/reintroductions have little probability of success. Several attempts have been made to repatriate amphibians affected by chytridiomycosis in Europe, North America, the Caribbean and Africa but none have led to successful, long-term amphibian re-establishment [4,26,28,29] (but see [30] for evidence of shortterm post-release survival). Although the majority of failures have been associated with the re-emergence of lethal chytridiomycosis in the translocated/reintroduced species, the cause behind failure to re-establish in almost every case could not be attributed clearly [26,28] (but see [11]).…”

“…These range from minimizing effects on host populations to pathogen eradication. Short-term solutions have been discussed in detail or summarized elsewhere and these are considered vital in temporarily preserving amphibian populations at risk [4,6,15,16]. For example, interventions with antifungals during an epidemic can alter infection dynamics and alleviate disease, but in the absence of long-term disease management in situ, any short-term measure is unlikely to result in significant conservation success [17].…”

“…Unfortunately, the development of field interventions for disease management has lagged far behind and managing amphibian health in nature remains a largely unexplored topic [4][5][6]. Because applied conservation always operates under enormous financial constraints, it is important to critically assess the viability of conservation strategies before significant investment, which has rarely been done for strategies for controlling chytridiomycosis in wild amphibians [6 -8].…”

Using site-occupancy models to prepare for the spread of chytridiomyosis and identify factors affecting detectability of a cryptic susceptible species, the Tasmanian tree frog

“…It is important to investigate a broad range of potential solutions. Experimental ideas include control of reservoir species, treatment and vaccination of hosts, disinfection of water bodies, bio-augmentation of hosts with inhibitory bacteria; and habitat modification, such as increased salinity (Woodhams et al 2011). As infected frog populations can thrive in naturally suboptimal habitats for the fungus (Puschendorf et al 2011), eradication of disease is not necessary for successful mitigation and any method that limits the impact of the disease is worthy of investigation.…”

BASELINE CUTANEOUS BACTERIA OF FREE-LIVING NEW ZEALAND NATIVE FROGS (LEIOPELMA ARCHEYIANDLEIOPELMA HOCHSTETTERI) AND IMPLICATIONS FOR THEIR ROLE IN DEFENSE AGAINST THE AMPHIBIAN CHYTRID (BATRACHOCHYTRIUM DENDROBATIDIS)

“…In some frog species, individuals with inhibitory bacteria resist Bd while those individuals without these beneficial bacteria may become infected (Harris et al 2009). Using probiotic symbiotic bacteria as a treatment to protect amphibians against chytridiomycosis has had mixed success (Harris et al 2009;Becker et al 2011;Woodhams et al 2011).…”