COS 279-4 - Evidence of nematodes (Caenorhabditis elegans) as alternative hosts for Batrachochytrium salamandrivorans (Bsal)

Background/Question/Methods

Given the global amphibian declines caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), the congener, Batrachochytrium salamandrivorans (Bsal), has become a pathogen of concern. In the short time since it was first described, Bsal has proven itself to be similarly deadly as Bd, causing staggering declines in susceptible salamander populations. Bd and Bsal are well known to be transmitted within and among amphibian species, but a more thorough understanding of potential alternative hosts is necessary to further understand how Bsal can spread and persist in the environment. There is evidence to support that Bd has potential alternative hosts, such as nematodes, which are prolific in soil environments. Because salamanders often have a terrestrial life stage, if soil nematodes serve as reservoir hosts for Bsal, they could be important for the persistence of Bsal in the environment. To assess how Bsal survival and growth are affected by nematodes, we crossed Bsal and nematode (Caenorhabditis elegans) presence and reared them on bacto-agar plates for 60 days. We destructively counted live and dead nematodes and zoospores on subsets of plates every 4 days.

Results/Conclusions

Nematodes consumed live and dead zoospores, and Bsal appeared to be endoparasites of live nematodes, emerging from both the vulva and anus. Z-stacked epifluorescence images of preserved nematodes revealed mature zoosporangia emerging primarily from the vulva, and live and dead zoospores scattered throughout the nematode’s body. These observations indicate that Bsal acts as an endoparasite of nematodes in a similar manner to other Chytridiomycota fungal parasites of nematodes. Additionally, while predatory nematodes may be capable of removing Bsal from the environment, they may also aid in Bsal’s persistence by also serving as a host, which could potentially complicate mitigation strategies. Ongoing studies are exploring whether nematodes decrease or increase the persistence of Bsal in the environment.