Review
Biological Concepts for the Control of Aquatic Zoosporic Diseases

https://doi.org/10.1016/j.pt.2019.04.003Get rights and content

Highlights

  • Aquatic zoosporic diseases pose a threat to biodiversity, ecosystem services, and economic activities.

  • Current control methods are based on the use of chemicals that have large negative side-effects.

  • To support the development of alternative biological control strategies, we outline seven general biological concepts to control zoosporic diseases.

  • We discuss some of the research required to successfully apply biological control strategies in the future.

Aquatic zoosporic diseases are threatening global biodiversity and ecosystem services, as well as economic activities. Current means of controlling zoosporic diseases are restricted primarily to chemical treatments, which are usually harmful or likely to be ineffective in the long term. Furthermore, some of these chemicals have been banned due to adverse effects. As a result, there is a need for alternative methods with minimal side-effects on the ecosystem or environment. Here, we integrate existing knowledge of three poorly interconnected areas of disease research – amphibian conservation, aquaculture, and plankton ecology – and arrange it into seven biological concepts to control zoosporic diseases. These strategies may be less harmful and more sustainable than chemical approaches. However, more research is needed before safe application is possible.

Section snippets

Aquatic Zoosporic Diseases and Biological Control

Emerging infectious diseases (see Glossary) present a worldwide threat to food security and ecosystem health 1., 2.. Amongst these are zoosporic diseases, caused by fungi or water molds (oomycetes) that require a wet or moist environment to survive and which are able to infect a diverse range of organisms, including prokaryotes, fungi, plants, arthropods, and vertebrates 3., 4.. The infectious stages of zoosporic pathogens (i.e., zoospores) use flagella to actively swim and potentially navigate

Amphibians

The development of methods to treat chytridiomycosis is currently focused either on reducing or eliminating the pathogen from the environment or on increasing the capacity of populations to persist despite increased mortality from disease, for example, by minimizing other sources of mortality [27]. Successfully tested in situ methods inhibiting fungal growth rely on the use of disinfectants or antifungal agents (fungicides) 28., 29., 30., or on temporarily modifying environmental conditions

Biological Control Strategies: New Solutions to Old Problems?

Currently, a variety of biological control strategies have been discussed across the three different areas of research, which we summarize here in seven general concepts (Table 1, Key Table).

The Role of the (Changing) Environment

The outcome of host–parasite encounters is often modulated by the external environment [101], making it challenging to predict and control disease outbreak and spread, especially under rapidly changing or unpredictable conditions as caused by global change. For example, the pattern of temperature-dependent growth of Bd on frogs was opposite to the pattern of growth in culture (on broth), emphasizing the importance of the environment in which parasites are studied when predicting

Concluding Remarks

In conclusion, we outline seven different biological-control concepts and propose immediate research needs that will help to progress their development. From our review it is apparent that we are only at the beginning of understanding what kind of biological zoosporic disease control strategies exist, and what potential they have. Much work still needs to be done to further advance our understanding of the interaction between hosts, pathogens, and the environment, to successfully implement

Outstanding Questions

  • How much do aquatic zoosporic diseases contribute to the death of organisms in the environment and production facilities?

  • Will climate change worsen the occurrence and spread of aquatic zoosporic diseases?

  • Why are some zoosporic parasites so efficient at killing their host?

  • How common is hyperparasitism on zoosporic parasites, and can it prevent infection of the primary host?

  • Can probiotics be beneficial to one host, and simultaneously function as antibiotics to other organisms?

  • What are the

Acknowledgments

This research was supported by the International IGB Fellowship Program ‘Freshwater Science’ of the Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB, Berlin) to T.F. and by the project People, Pollution, and Pathogens financed through the call ‘Mountains as Sentinels of Change’ by the Belmont Forum (ANR-15-MASC-0001 - P3, DFG-SCHM 3059/6-1, NERC-1633948, NSFC-41661144004) to D.S.S. and funding from the BBSRC and the NERC to P.v.W. The authors would like to thank Mark Phillipo

Glossary

Biodiversity
diversity of life forms, for example, indicated by the number of different species.
Biofuel
fuel produced from biological materials (in contrast to fossil fuels which are produced by geological processes), for example, from plants or plankton.
Biological control
an approach that applies understanding of organisms and their ecological interactions within an ecosystem to eliminate or reduce unwanted organisms.
Dilution effect
a phenomenon observed in communities comprised of species with

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