Bd In Amphibians Research Articles

Water Pollution Increases the Risk of Chytridiomycosis in Mexican Amphibians

Chytridiomycosis is affecting amphibians worldwide, causing the decline and extinction of several amphibian populations. The disease is caused by the fungus Batrachochytrium dendrobatidis (Bd), a multihost pathogen living in freshwater habitats. While several environmental factors have been associated with the prevalence of Bd and its virulence, the effects of water quality on the pathogen are not clear yet. Some evidence suggests that water pollution may reduce amphibians' immune response and increase prevalence of Bd. To explore this hypothesis, we analyzed the relationship between water quality and the presence of Bd by using spatial data mining of 150 geolocations of Bd in amphibians from 9 families where Bd positive specimens have been previously reported, and water quality in 4,202 lentic and lotic water bodies in Mexico from 2010 to 2021. Our model showed that in the 3 main families where Bd was recorded, its presence is high in locations with low water quality, i.e., water polluted likely contaminated with urban and industrial waste. Using this model, we inferred areas suitable for Bd in Mexico; mainly in poorly studied areas along the gulf and on the pacific slope. We further argue that actions to reduce water pollution should become an integral part of public policies to prevent the spread of Bd and protect amphibians from this deadly pathogen.

The invasive red swamp crayfish (Procambarus clarkii) increases infection of the amphibian chytrid fungus (Batrachochytrium dendrobatidis)

Emerging infectious diseases are increasingly recognized as a severe threat to wildlife. Chytridiomycosis, caused by Batrachochytrium dendrobatidis (Bd), is considered one of the most important causes for the decline of amphibian populations worldwide. Identifying potential biological reservoirs and characterizing the role they can play in pathogen maintenance is not only important from a scientific point of view, but also relevant from an applied perspective (e.g. disease control strategies), especially when worldwide distributed invasive species are involved. We aimed (1) to analyse the prevalence and infection intensity of Bd in the invasive red swamp crayfish (Procambarus clarkii) across the western Andalusian region in Spain; and (2) to assess whether the presence of crayfish affects the prevalence and infection intensity of Bd in amphibians of Donana Natural Space (DNS), a localized highly protected area within the Andalusian region. First, we found that infection prevalence in crayfish guts was 1.5% regionally (four out of 267 crayfish were qPCR positive to Bd, all of them belonging to the same Andalusian population); qPCR positives were histologically confirmed by finding zoosporangia of Bd in gastrointestinal walls of the red swamp crayfish. Second, we found a higher prevalence of Bd infection in DNS (19% for crayfish and 28% for amphibians on average), a place with great diversity and abundance of amphibians. Our analyses showed that prevalence of Bd in amphibians was related to the presence of the red swamp crayfish, indicating that this crayfish could be a suitable predictor of Bd infection in co-occurring amphibians. These results suggest that the red swamp crayfish might be a possible reservoir for Bd, representing an additional indirect impact on amphibians, a role that had not been previously recognised in its invasive range.

Validation and cost-effectiveness of an alternative method to quantify Batrachochytrium dendrobatidis infection in amphibian samples using real-time PCR

The chytrid fungus Batrachochytrium dendrobatidis (Bd) is considered one of the main causes of amphibian declines worldwide. Detection of Bd infection relies on both histological and molecular techniques, but only quantitative real-time PCR (qPCR) provides quantitative information on intensity of infection. To quantify Bd infection, Boyle et al. (2004) developed a standard method using TaqMan qPCR assay: however, the high costs of this method can hinder its applicability for studies with limited resources. Starting from the method by Boyle et al. (2004), we set up and fully validated a qPCR assay based on modified primers and SYBR Green chemistry. The modified SYBR Green has high sensitivity and specificity, as well as the ability to quantify Bd infection loads as well as the standard TaqMan qPCR, but it is more than 60% cheaper. This is obtained both by intrinsic cost-effectiveness of the SYBR Green technique and by reducing reaction volumes of qPCR. Therefore, this modified qPCR assay constitutes a cheaper molecular method to quantify Bd in amphibians.

Amphibian trade and the presence of Batrachochytrium dendrobatidis in free-ranging: dispersion in vicious circle?

The amphibian trade has an important role in Batrachochytrium dendrobatidis (Bd) persistence, for at least 28 amphibian species can serve as vectors. The objectives of this work are to evaluate the presence and prevalence of Bd in amphibian traded in two petshops in Mexico City, as well as to verify their presence in wild amphibian populations of species traded. It was found that 92% of amphibians sold in the two petshops were captured free-living, and 37.3% of these animals were infected with Bd, according to histological analysis. The prevalence of 30.8% of Bd in wild amphibians at the wild capture sites was detected by means of DNA amplification. No significant differences were found between prevalence of wild and trade amphibians, but the trend was higher for trade amphibians. The importance of amphibian management and conservation plans has been growing in the last years. The pet trade and its capture from the wild turn these trade routes and their captive management into means of pathogenic dispersion, which may increase the risk of disease outbreaks.Keywords: Chytridiomycosis, pet trade, optical microscopy, nested PCR.

Long-term monitoring of tropical alpine habitat change, Andean anurans, and chytrid fungus in the Cordillera Vilcanota, Peru: Results from a decade of study.

The Cordillera Vilcanota in southern Peru is the second largest glacierized range in the tropics and home to one of the largest high‐alpine lakes, Sibinacocha (4,860 m). Here, Telmatobius marmoratus (marbled water frog), Rhinella spinulosa (Andean toad), and Pleurodema marmoratum (marbled four‐eyed frog) have expanded their range vertically within the past century to inhabit newly formed ponds created by ongoing deglaciation. These anuran populations, geographically among the highest (5,200–5,400 m) recorded globally, are being impacted by the chytrid fungus Batrachochytrium dendrobatidis (Bd), and the disease it causes, chytridiomycosis. In this study, we report results from over a decade of monitoring these three anuran species, their habitat, and Bd infection status. Our observations reveal dynamic changes in habitat including ongoing rapid deglaciation (18.4 m/year widening of a corridor between retreating glaciers from 2005 to 2015), new pond formation, changes in vegetation in amphibian habitat, and widespread occurrence of Bd in amphibians in seven sites. Three of these sites have tested positive for Bd over a 9‐ to 12‐year period. In addition, we observed a widespread reduction in T. marmoratus encounters in the Vilcanota in 2008, 2009, and 2012, while encounters increased in 2013 and 2015. Despite the rapid and dynamic changes in habitat under a warming climate, continued presence of Bd in the environment for over a decade, and a reduction in one of three anuran species, we document that these anurans continue to breed and survive in this high Andean environment. High variability in anuran encounters across sites and plasticity in these populations across habitats, sites, and years are all factors that could favor repopulation postdecline. Preserving the connectivity of wetlands in the Cordillera Vilcanota is therefore essential in ensuring that anurans continue to breed and adapt as climate change continues to reshape the environment.

Invasion of the Fungal Pathogen Batrachochytrium dendrobatidis on California Islands.

Batrachochytrium dendrobatidis (Bd), an amphibian fungal pathogen, has infected >500 species and caused extinctions or declines in >200 species worldwide. Despite over a decade of research, little is known about its invasion biology. To better understand this, we conducted a museum specimen survey (1910-1997) of Bd in amphibians on 11 California islands and found a pattern consistent with the emergence of Bd epizootics on the mainland, suggesting that geographic isolation did not prevent Bd invasion. We propose that suitable habitat, host diversity, and human visitation overcome isolation from the mainland and play a role in Bd invasion.

Pathogenic fungus Batrachochytrium dendrobatidis in marbled water frog Telmatobius marmoratus: first record from Lake Titicaca, Bolivia.

The pathogenic fungus Batrachochytrium dendrobatidis (Bd) has been associated with amphibian declines worldwide but has not been well-studied among Critically Endangered amphibian species in Bolivia. We sampled free-living marbled water frogs Telmatobius marmoratus (Anura: Leptodactylidae) from Isla del Sol, Bolivia, for Bd using skin swabs and quantitative polymerase chain reactions. We detected Bd on 44% of T. marmoratus sampled. This is the first record of Bd in amphibians from waters associated with Lake Titicaca, Bolivia. These results further confirm the presence of Bd in Bolivia and substantiate the potential threat of this pathogen to the Critically Endangered, sympatric Titicaca water frog T. culeus and other Andean amphibians.

First Evidence of Batrachochytrium dendrobatidis in China: Discovery of Chytridiomycosis in Introduced American Bullfrogs and Native Amphibians in the Yunnan Province, China

Although the chytrid fungus Batrachochytrium dendrobatidis (Bd), the etiological agent of amphibian chytridiomycosis, has been implicated in mass mortality and population declines on several continents around the world, there have been no reports on the presence of Bd infections in amphibians in China. We employed quantitative PCR and histological techniques to investigate the presence of Bd in introduced North American bullfrogs (Rana catesbeiana) (referred to hereafter as bullfrog) and native amphibians in bullfrog-invaded areas of the Yunnan Province, China. A total of 259 samples at five wild sites were collected between June and September in 2007 and 2008, including bullfrogs and four native amphibian species (Rana pleuraden, Rana chaochiaoensis, Odorrana andersonii, and Bombina maxima). In addition, 37 samples of adult bullfrogs were obtained from a food market. Bd infections were discovered in bullfrogs and three native amphibian species from all of the surveyed sites. Of the 39 Bd-positive samples, 35 were from wild-caught bullfrog tadpoles, postmetamorphic bullfrogs, R. pleuraden, R. chaochiaoensis, and O. andersonii, and four were from adult bullfrogs from the market. Our results provide the first evidence of the presence of Bd in Chinese amphibians, suggesting that native amphibian diversity in China is at risk from Bd. There is an urgent need to monitor the distribution of Bd in amphibians in China and understand the susceptibility of native amphibian species to chytridiomycosis. Strict regulations on the transportation of bullfrogs and the breeding of bullfrogs in markets and farms should be drafted in order to stop the spread of Bd by bullfrogs.