Limits...
Disentangling host, pathogen, and environmental determinants of a recently emerged wildlife disease: lessons from the first 15 years of amphibian chytridiomycosis research.

James TY, Toledo LF, Rödder D, da Silva Leite D, Belasen AM, Betancourt-Román CM, Jenkinson TS, Soto-Azat C, Lambertini C, Longo AV, Ruggeri J, Collins JP, Burrowes PA, Lips KR, Zamudio KR, Longcore JE - Ecol Evol (2015)

Bottom Line: We explore factors associated with variance in severity of epizootics focusing on the disease triangle of host susceptibility, pathogen virulence, and environment.Instead of focusing on pathogen "hot spots," we need to identify pathogen "cold spots" so that we can better understand what limits the pathogen's distribution.Finally, we introduce the concept of "the Ghost of Epizootics Past" to discuss expected patterns in postepizootic host communities.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology University of Michigan Ann Arbor Michigan 48109.

ABSTRACT
The amphibian fungal disease chytridiomycosis, which affects species across all continents, recently emerged as one of the greatest threats to biodiversity. Yet, many aspects of the basic biology and epidemiology of the pathogen, Batrachochytrium dendrobatidis (Bd), are still unknown, such as when and from where did Bd emerge and what is its true ecological niche? Here, we review the ecology and evolution of Bd in the Americas and highlight controversies that make this disease so enigmatic. We explore factors associated with variance in severity of epizootics focusing on the disease triangle of host susceptibility, pathogen virulence, and environment. Reevaluating the causes of the panzootic is timely given the wealth of data on Bd prevalence across hosts and communities and the recent discoveries suggesting co-evolutionary potential of hosts and Bd. We generate a new species distribution model for Bd in the Americas based on over 30,000 records and suggest a novel future research agenda. Instead of focusing on pathogen "hot spots," we need to identify pathogen "cold spots" so that we can better understand what limits the pathogen's distribution. Finally, we introduce the concept of "the Ghost of Epizootics Past" to discuss expected patterns in postepizootic host communities.

No MeSH data available.


Related in: MedlinePlus

Batrachochytrium dendrobatidis develops by either of two pathways, depending on whether growth is on nutrient agar (A–E; Longcore et al. 1999) or inside of amphibian cells (A, F, I; Greenspan et al. 2012). On agar, the zoospore (A) encysts and forms anucleate rhizoids. Over the course of 4 days (A–D), the zoospore cyst matures into a zoosporangium that releases zoospores through discharge papillae (E). Colonial thalli divided by septae (arrow) occur occasionally (B′), and their presence has been used to confirm the identity of B. dendrobatidis. On skin, the zoospore encysts on the surface of a cell (F), and forms a germ tube (arrow), which grows through one or more host cell layers (G). The zoosporangium with sparse rhizoids forms from a swelling of the germ tube (G, H). By the time zoospores are released, the outer skin layer (arrow) has sloughed (I).
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ece31672-fig-0001: Batrachochytrium dendrobatidis develops by either of two pathways, depending on whether growth is on nutrient agar (A–E; Longcore et al. 1999) or inside of amphibian cells (A, F, I; Greenspan et al. 2012). On agar, the zoospore (A) encysts and forms anucleate rhizoids. Over the course of 4 days (A–D), the zoospore cyst matures into a zoosporangium that releases zoospores through discharge papillae (E). Colonial thalli divided by septae (arrow) occur occasionally (B′), and their presence has been used to confirm the identity of B. dendrobatidis. On skin, the zoospore encysts on the surface of a cell (F), and forms a germ tube (arrow), which grows through one or more host cell layers (G). The zoosporangium with sparse rhizoids forms from a swelling of the germ tube (G, H). By the time zoospores are released, the outer skin layer (arrow) has sloughed (I).

Mentions: A major reason for this focus on Bd is that it is a generalist amphibian pathogen and close to 41% of amphibians are threatened, making them one of the most threatened vertebrate lineages (Monastersky 2014). Bd emergence demonstrates that host–pathogen interactions can play a major role in species declines and even extinctions (Crawford et al. 2010). Bd has now been reported from over 500 amphibian host species, has a cosmopolitan distribution, and has been detected at 48% of localities that have been surveyed (Olson et al. 2013). This wide distribution has been documented just since chytridiomycosis was first described (Longcore et al. 1999), when it was the first known vertebrate pathogen from an obscure phylum of fungi whose mechanism of pathogenesis and life cycle (Fig. 1) were incompletely known. This obscurity has meant studies on the biology of the pathogen have lagged behind those of hosts. Indeed, most of the questions that the research community set out to answer when the disease was first described, including “Where did it come from?”, “How does it spread?”, “Why are some species resistant or tolerant?”, “Does it have an alternate host or environmental stage?”, and “Why now?”, have yet to be definitively answered (Collins and Crump 2009; Kilpatrick et al. 2010).


Disentangling host, pathogen, and environmental determinants of a recently emerged wildlife disease: lessons from the first 15 years of amphibian chytridiomycosis research.

James TY, Toledo LF, Rödder D, da Silva Leite D, Belasen AM, Betancourt-Román CM, Jenkinson TS, Soto-Azat C, Lambertini C, Longo AV, Ruggeri J, Collins JP, Burrowes PA, Lips KR, Zamudio KR, Longcore JE - Ecol Evol (2015)

Batrachochytrium dendrobatidis develops by either of two pathways, depending on whether growth is on nutrient agar (A–E; Longcore et al. 1999) or inside of amphibian cells (A, F, I; Greenspan et al. 2012). On agar, the zoospore (A) encysts and forms anucleate rhizoids. Over the course of 4 days (A–D), the zoospore cyst matures into a zoosporangium that releases zoospores through discharge papillae (E). Colonial thalli divided by septae (arrow) occur occasionally (B′), and their presence has been used to confirm the identity of B. dendrobatidis. On skin, the zoospore encysts on the surface of a cell (F), and forms a germ tube (arrow), which grows through one or more host cell layers (G). The zoosporangium with sparse rhizoids forms from a swelling of the germ tube (G, H). By the time zoospores are released, the outer skin layer (arrow) has sloughed (I).
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

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ece31672-fig-0001: Batrachochytrium dendrobatidis develops by either of two pathways, depending on whether growth is on nutrient agar (A–E; Longcore et al. 1999) or inside of amphibian cells (A, F, I; Greenspan et al. 2012). On agar, the zoospore (A) encysts and forms anucleate rhizoids. Over the course of 4 days (A–D), the zoospore cyst matures into a zoosporangium that releases zoospores through discharge papillae (E). Colonial thalli divided by septae (arrow) occur occasionally (B′), and their presence has been used to confirm the identity of B. dendrobatidis. On skin, the zoospore encysts on the surface of a cell (F), and forms a germ tube (arrow), which grows through one or more host cell layers (G). The zoosporangium with sparse rhizoids forms from a swelling of the germ tube (G, H). By the time zoospores are released, the outer skin layer (arrow) has sloughed (I).
Mentions: A major reason for this focus on Bd is that it is a generalist amphibian pathogen and close to 41% of amphibians are threatened, making them one of the most threatened vertebrate lineages (Monastersky 2014). Bd emergence demonstrates that host–pathogen interactions can play a major role in species declines and even extinctions (Crawford et al. 2010). Bd has now been reported from over 500 amphibian host species, has a cosmopolitan distribution, and has been detected at 48% of localities that have been surveyed (Olson et al. 2013). This wide distribution has been documented just since chytridiomycosis was first described (Longcore et al. 1999), when it was the first known vertebrate pathogen from an obscure phylum of fungi whose mechanism of pathogenesis and life cycle (Fig. 1) were incompletely known. This obscurity has meant studies on the biology of the pathogen have lagged behind those of hosts. Indeed, most of the questions that the research community set out to answer when the disease was first described, including “Where did it come from?”, “How does it spread?”, “Why are some species resistant or tolerant?”, “Does it have an alternate host or environmental stage?”, and “Why now?”, have yet to be definitively answered (Collins and Crump 2009; Kilpatrick et al. 2010).

Bottom Line: We explore factors associated with variance in severity of epizootics focusing on the disease triangle of host susceptibility, pathogen virulence, and environment.Instead of focusing on pathogen "hot spots," we need to identify pathogen "cold spots" so that we can better understand what limits the pathogen's distribution.Finally, we introduce the concept of "the Ghost of Epizootics Past" to discuss expected patterns in postepizootic host communities.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Evolutionary Biology University of Michigan Ann Arbor Michigan 48109.

ABSTRACT
The amphibian fungal disease chytridiomycosis, which affects species across all continents, recently emerged as one of the greatest threats to biodiversity. Yet, many aspects of the basic biology and epidemiology of the pathogen, Batrachochytrium dendrobatidis (Bd), are still unknown, such as when and from where did Bd emerge and what is its true ecological niche? Here, we review the ecology and evolution of Bd in the Americas and highlight controversies that make this disease so enigmatic. We explore factors associated with variance in severity of epizootics focusing on the disease triangle of host susceptibility, pathogen virulence, and environment. Reevaluating the causes of the panzootic is timely given the wealth of data on Bd prevalence across hosts and communities and the recent discoveries suggesting co-evolutionary potential of hosts and Bd. We generate a new species distribution model for Bd in the Americas based on over 30,000 records and suggest a novel future research agenda. Instead of focusing on pathogen "hot spots," we need to identify pathogen "cold spots" so that we can better understand what limits the pathogen's distribution. Finally, we introduce the concept of "the Ghost of Epizootics Past" to discuss expected patterns in postepizootic host communities.

No MeSH data available.


Related in: MedlinePlus