Detection of pathogenic Batrachochytrium dendrobatidis using water filtration, animal and bait testing

Abstract

The pathogen Batrachochytrium dendrobatidis (Bd) can be challenging to detect at endangered amphibian reintroduction sites. Pre-release Bd detection can be confounded by imperfect animal sampling and the absence of animals. In Study 1, we used historical Bd-positive sites, to concurrently evaluate water filtrates and mouth bar (tadpoles) or skin swab (caudates) samples for Bd using molecular beacon realtime PCR. In Study 2, during a natural outbreak, we used PCR to detect Bd from zoospore-attracting keratin baits (three avian, three snake species). In Study 1, no captured animals (n=116) exhibited clinical signs, although 10.6% were positive, representing three of seven species sampled. In contrast, 5.4% of water filters (n=56) were Bd-positive. In Study 2, after short incubation times, a single duck down feather tested Bd-positive. In conclusion, Bd was detected in asymptomatic amphibians and water filtrate at two sites, and from water only, at two other sites. With continued refinement, semi-quantitative Bd water filtrate screening could better define zoospore-specific disease risk, allowing better characterization of the free-living phase of the organism's life cycle. Finally, these results suggest wild aquatic birds (e.g., waterfowl) should be systematically explored as a means of Bd spread. Since large numbers of aquatic birds migrate, even low Bd transfer rates could be a significant means for disease dissemination.

Terrestrial Dispersal and Potential Environmental Transmission of the Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis)

“…Contact with contaminated water is another avenue, and Bd 's motile uniflagellated zoospores can disperse through a water body either by swimming short distances or by being carried in water currents [ 18 ]. Waterfowl might carry Bd between separate water bodies, either on their feathers or feet [ 19 – 21 ]. However, the high prevalence of Bd detected in terrestrial and arboreal amphibian species that infrequently contact each other and typically do not directly engage with other species or enter permanent water bodies [ 22 – 25 ], suggests the presence of additional avenues of Bd dispersal and environmental transmission.…”

Amphibian Disease Ecology: Are We Just Scratching the Surface?

“…Furthermore, most of the aforementioned factors influence epidemiological patterns on a local scale, but fail to fully explain how pathogens spread across the landscape and globally. At a local scale, the spread of infectious agents is likely mediated by human activities (e.g., Ranavirus on contaminated equipment, Casais et al 2019;and fishing bait, Picco et al 2010;Wimsatt et al 2014), but waterfowl can facilitate pathogen translocation in more complex landscapes (e.g., Bd; Garmyn et al 2012; Burrowes and De la Riva 2017; Hanlon et al 2017). At a continental scale, amphibian pathogens are regularly spread through commercial activities (pet and food trade; Kolby et al 2014;Wombwell et al 2016;O'Hanlon et al 2018;Yuan et al 2018), and this needs to be rigorously prevented.…”

Risk of survival, establishment and spread of Batrachochytrium salamandrivorans (Bsal) in the EU

“…For Bd: Feathers and feet of waterfowl in experimental and natural conditions (Johnson and Speare, ; Garmyn et al., ; Wimsatt et al., ; Hanlon et al., )…”

“…Also, frogs and toads could be Bsal carriers (Nguyen et al, 2017;Stegen et al, 2017) and these amphibians can move from hundreds of metres up to several kilometres during migrations (Tunner, 1991;Kovar et al, 2009). In addition, waterfowl carrying spores of the sister species Bd on skin or feathers have been reported (Wimsatt et al, 2014).…”