Validation of Diagnostic Tests in Wildlife: The Case of Chytridiomycosis in Wild Amphibians

Skerratt, Lee F.; Méndez, Diana; McDonald, Keith; Garland, SM; Livingstone, James; Berger, Lee; Speare, Rick

doi:10.1670/10-193.1

Cited by 49 publications

(49 citation statements)

References 25 publications

(53 reference statements)

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“…We used two methods: (i) epithelial swabbing and (ii) histology of phalanges to sample for Bd [44], [45]. Cotton swabs were utilised to brush the Bd sensitive areas of each individual live frog including the ventral surface of each thigh, hind foot and pelvis.…”

Section: Methodsmentioning

confidence: 99%

West Africa - A Safe Haven for Frogs? A Sub-Continental Assessment of the Chytrid Fungus (Batrachochytrium dendrobatidis)

et al. 2013

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A putative driver of global amphibian decline is the panzootic chytrid fungus Batrachochytrium dendrobatidis (Bd). While Bd has been documented across continental Africa, its distribution in West Africa remains ambiguous. We tested 793 West African amphibians (one caecilian and 61 anuran species) for the presence of Bd. The samples originated from seven West African countries - Bénin, Burkina Faso, Côte d'Ivoire, Ghana, Guinea, Liberia, Sierra Leone - and were collected from a variety of habitats, ranging from lowland rainforests to montane forests, montane grasslands to humid and dry lowland savannahs. The species investigated comprised various life-history strategies, but we focused particularly on aquatic and riparian species. We used diagnostic PCR to screen 656 specimen swabs and histology to analyse 137 specimen toe tips. All samples tested negative for Bd, including a widespread habitat generalist Hoplobatrachus occipitalis which is intensively traded on the West African food market and thus could be a potential dispersal agent for Bd. Continental fine-grained (30 arc seconds) environmental niche models suggest that Bd should have a broad distribution across West Africa that includes most of the regions and habitats that we surveyed. The surprising apparent absence of Bd in West Africa indicates that the Dahomey Gap may have acted as a natural barrier. Herein we highlight the importance of this Bd-free region of the African continent - especially for the long-term conservation of several threatened species depending on fast flowing forest streams (Conraua alleni (“Vulnerable”) and Petropedetes natator (“Near Threatened”)) as well as the “Critically Endangered” viviparous toad endemic to the montane grasslands of Mount Nimba (Nimbaphrynoides occidentalis).

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Section: Methodsmentioning

confidence: 99%

West Africa - A Safe Haven for Frogs? A Sub-Continental Assessment of the Chytrid Fungus (Batrachochytrium dendrobatidis)

et al. 2013

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“…Samples were considered as positive when threshold cycle values (PCR cycle at point of detection) were equal to or exceeded the level for 11 copies of the target fragment, which corresponds to about 0.1 zoospore genomic equivalents (Kirshtein et al 2007), a common standard that can still be reliably amplified (e.g. Boyle et al 2004, Skerratt et al 2011. Sam ples found to be positive in the first round were tested a second time to confirm the result and reduce the number of false positive counts probably caused by contamination in the laboratory (Skerratt et al 2011).…”

Section: Dna Preparation and Bd Detection Testsmentioning

confidence: 99%

“…Boyle et al 2004, Skerratt et al 2011. Sam ples found to be positive in the first round were tested a second time to confirm the result and reduce the number of false positive counts probably caused by contamination in the laboratory (Skerratt et al 2011). …”

Section: Dna Preparation and Bd Detection Testsmentioning

confidence: 99%

Batrachochytrium dendrobatidis in Germany: distribution, prevalences, and prediction of high risk areas

Ohst¹,

Gräser²,

Plötner³

2013

Dis. Aquat. Org.

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In Germany, the pathogenic fungus Batrachochytrium dendrobatidis (Bd) was detected in 11 indigenous frog species, 4 newt species, and 1 salamander species in 64 out of the 181 locations (35%) investigated. Among the 3450 samples collected between 2003 and 2011, 284 (8.2%) were positive for Bd infections. The highest prevalences were observed in Alytes obstetricans (17.8% of individuals, 20% of populations), followed by Ichthyosaura alpestris (14.7%, 22.2%), Bombina variegata (13.9%, 38.5%), and water frogs comprising 2 species, Pelophylax lessonae and P. ridibundus, and their hybrid form P. esculentus (13.5%, 29.0%). Bd is widespread; areas of higher prevalence were detected in eastern, southeastern, western, and southwestern Germany. Our data indicate that drift fencing of amphibians is not a risk factor for the anthropogenic spread of Bd. Although chytridiomycosis outbreaks have never been observed in Germany, it cannot be excluded that Bd infections affect the dynamics of local amphibian populations. Among the questions still to be answered is whether juveniles are more susceptible to Bd infections than adults. Further work, especially long-term observations including capture-mark-recapture studies, is required to clarify the impact Bd has on amphibians in Germany and Central Europe. KEY WORDS: Batrachochytrium dendrobatidis · Chytridiomycosis · Germany · Distribution · Prevalence · Amphibian fencing Resale or republication not permitted without written consent of the publisherDis Aquat Org 107: [49][50][51][52][53][54][55][56][57][58][59] 2013 2005, Schmidt et al. 2009), Italy (Federici et al. 2008, and on Sardinia (Bovero et al. 2008, Bielby et al. 2009). Epidemiological data from the northern and eastern parts of Europe, however, are scarce.In Germany, the first field record of Bd was obtained from the water frog hybrid Pelophylax esculentus, which was sampled in the state of Brandenburg, northeastern Germany (Mutschmann et al. 2000). Further records originated from P. esculentus, found in 2003 near Neuwied (Rhineland-Palatinate), Triturus alpestris (2001 and 2003) collected in southern Germany (Swabian Alb), and Salamandra salamandra (2001 and 2002) kept in an outdoor terrarium (Mutschmann 2007). Preliminary prevalence data ob tained from all indigenous German amphibian species except S. atra indicate that Bd is widespread in Germany and is able to infect all species (Ohst et al. 2011). Chytridiomycosis outbreaks, however, have never been observed; therefore the role Bd plays in population declines in Germany, as in the whole of Central Europe, is not yet clear. We therefore as a first step estimated species-, population-, and locality-specific prevalence rates of Bd infections in Germany. Based on 3450 tissue samples from 181 localities, we aimed to explore the spatial patterns of Bd infections and detect areas of increased Bd prevalences in Germany as a basis for risk assessment and conservation management.Despite the role Bd plays in the dynamics of am phibian populations, destruction,...

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“…Pathogen overdispersion, another feature well recognized as common to macroparasites, occurs with chytridiomycosis (Skerratt et al . ), but its underlying causes and effects on disease dynamics have not been investigated. Pathogen overdispersion (otherwise known as parasite aggregation, pathogen aggregation or pathogen distribution heterogeneity) describes a distribution of infectious organisms among hosts whereby most infected individuals have low infectious burdens, while very few hosts have high burdens.…”

Section: Introductionmentioning

confidence: 99%

Endemicity of chytridiomycosis features pathogen overdispersion

Grogan

Phillott

Scheele

et al. 2016

Journal of Animal Ecology

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Pathogens can be critical drivers of the abundance and distribution of wild animal populations. The presence of an overdispersed pathogen load distribution between hosts (where few hosts harbour heavy parasite burdens and light infections are common) can have an important stabilizing effect on host-pathogen dynamics where infection intensity determines pathogenicity. This may potentially lead to endemicity of an introduced pathogen rather than extirpation of the host and/or pathogen. Overdispersed pathogen load distributions have rarely been considered in wild animal populations as an important component of the infection dynamics of microparasites such as bacteria, viruses, protozoa and fungi. Here we examined the abundance, distribution and transmission of the model fungal pathogen Batrachochytrium dendrobatidis (Bd, cause of amphibian chytridiomycosis) between wild-caught Litoria rheocola (common mist frogs) to investigate the effects of an overdispersed pathogen load distribution on the host population in the wild. We quantified host survival, infection incidence and recovery probabilities relative to infectious burden, and compared the results of models where pathogen overdispersion either was or was not considered an important feature of host-pathogen dynamics. We found the distribution of Bd load between hosts to be highly overdispersed. We found that host survival was related to infection burden and that accounting for pathogen overdispersion allowed us to better understand infection dynamics and their implications for disease control. In addition, we found that the pattern of host infections and recoveries varied markedly with season whereby (i) infections established more in winter, consistent with temperature-dependent effects on fungal growth, and (ii) recoveries (loss of infection) occurred frequently in the field throughout the year but were less likely in winter. Our results suggest that pathogen overdispersion is an important feature of endemic chytridiomycosis and that intensity of infection determines disease impact. These findings have important implications for our understanding of chytridiomycosis dynamics and the application of management strategies for disease mitigation. We recommend quantifying individual infectious burdens rather than infection state where possible in microparasitic diseases.

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Validation of Diagnostic Tests in Wildlife: The Case of Chytridiomycosis in Wild Amphibians

Cited by 49 publications

References 25 publications

West Africa - A Safe Haven for Frogs? A Sub-Continental Assessment of the Chytrid Fungus (Batrachochytrium dendrobatidis)

West Africa - A Safe Haven for Frogs? A Sub-Continental Assessment of the Chytrid Fungus (Batrachochytrium dendrobatidis)

Batrachochytrium dendrobatidis in Germany: distribution, prevalences, and prediction of high risk areas

Endemicity of chytridiomycosis features pathogen overdispersion

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