Amphibian Pathogens in Southeast Asian Frog Trade

Abstract

Amphibian trade is known to facilitate the geographic spread of pathogens. Here we assess the health of amphibians traded in Southeast Asia for food or as pets, focusing on Batrachochytrium dendrobatidis (Bd), ranavirus and general clinical condition. Samples were collected from 2,389 individual animals at 51 sites in Lao PDR, Cambodia, Vietnam and Singapore for Bd screening, and 74 animals in Cambodia and Vietnam for ranavirus screening. Bd was found in one frog (n = 347) in Cambodia and 13 in Singapore (n = 419). No Bd was found in Lao PDR (n = 1,126) or Vietnam (n = 497), and no ranavirus was found in Cambodia (n = 70) or Vietnam (n = 4). Mild to severe dermatological lesions were observed in all East Asian bullfrogs Hoplobatrachus rugolosus (n = 497) sampled in farms in Vietnam. Histologic lesions consistent with sepsis were found within the lesions of three frogs and bacterial sepsis in two (n = 4); one had Gram-negative bacilli and one had acid-fast organisms consistent with mycobacterium sp. These results confirm that Bd is currently rare in amphibian trade in Southeast Asia. The presence of Mycobacterium-associated disease in farmed H. rugolosus is a cause for concern, as it may have public health implications and indicates the need for improved biosecurity in amphibian farming and trade.

First Evidence of Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis) and Ranavirus in Hong Kong Amphibian Trade

“…Due to the narrow diversity of native amphibian species previously evaluated for Bd infection and sampling bias towards post-metamorphic specimens, it remains possible that amphibian pathogens have evaded detection. Previous surveys throughout Asia have generally demonstrated widespread Bd distribution at low prevalence, and have provided some evidence for the presence of an endemic Asian lineage of Bd [5], [29], [31], [33]. Therefore, although the possibility of an historic introduction of Bd and long-term presence in Hong Kong cannot be fully disregarded, the absence of both prior detection and disease-suspected population declines suggests this phenomenon would be of low conservation concern relative to the contemporary importation of exotic disease strains that typically express higher virulence than strains considered endemic to the region [20], [34].…”

One Health, emerging infectious diseases and wildlife: two decades of progress?

“…Subsequent research indicates that this is only part of the story, as it appears that the global pandemic lineage of B. dendrobatidis arose from a single hybrid origin via an ancestral meiosis, possibly via the anthropogenic mixing of allopatric lineages [68,69]. There is a substantial volume of research that shows how, once evolved, this virulent lineage has been introduced globally via the international trade in amphibians and via the human-assisted introduction of invasive species [66,70–75]. …”

Understanding the drivers ofSoutheastAsian biodiversity loss

“…, Gilbert et al. , Kolby et al. ), and more stringent regulations may be necessary to prevent the possibility of future emergent diseases (Schloegel et al.…”

“…net), though data suggest that chytrid has been present in at least parts of Asia for over 100 years (Bai et al 2012, Fong et al 2015 and has not been associated with large-scale declines, and evidence of adaptations to reduce the impact of the virus has also been detected in wild Asian amphibian populations (Harris et al 2009). Spread of both chytrid virus and ranavirus has been associated with markets and farmed animals, and the water they are kept and transported in (Bai et al 2012, Gilbert et al 2012, Kolby et al 2014, and more stringent regulations may be necessary to prevent the possibility of future emergent diseases (Schloegel et al 2012. A similar virus has been detected in Caudata (B. salamandrivorans), but has also not been associated with high death rates in Asia at this point in time, and is also thought to have originated in Asia (Martel et al 2014).…”