The impact of a disease on Southeast Asian frogs: a first look

A potentially deadly pathogen is infecting frogs in Vietnam, but is it causing frog population declines?

Many frog populations around the world have suffered dramatic population declines or even been driven to extinction from a disease-causing pathogen known as the amphibian chytrid fungus. Frogs population declines due to this fungus have been reported globally, but although the fungus is known to infect frogs in Southeast Asia, we don’t yet know if it is causing population declines. We surveyed frogs at a high-elevation forest site in Vietnam where the amphibian chytrid fungus is present and found no evidence of population declines. This is great news- suggesting that the frogs of the region may not be suffering dramatic population declines due to the amphibian chytrid fungus as they are in other regions.

The amphibian chytrid fungus (Batrachochytrium dendrobatidis, Bd), responsible for the potentially deadly disease chytridiomycosis, has been reported from frog populations throughout Asia, but there are no reports of sick or dead frogs or of population declines due to the disease. However, there hasn’t been much monitoring in the region, meaning that we simply don’t know if declines are occurring.

As a first step to understanding if frog species are declining from the amphibian chytrid fungus at a site in Southeast Asia, we surveyed frogs every month for 18 months at three streams in the high-elevation forests of Lam Dong Province in Vietnam. We knew that the fungus was present at the site, but not how the local frogs were responding.

Our study streams are in evergreen cloud forests with a diverse frog community. Almost 40 frog species have been reported from the area and at least six new frog species have been discovered there since 2010. We searched the streams at night, looking for frogs with headlamps and identifying each frog found.

We detected almost 3000 individuals of 19 frog species and found no evidence that frog populations were declining. In addition, we found no sick or dead frogs and all the frog species reported from the area during surveys in the early 1900s have recently been found.

Our results suggest that the frogs at the site (and we hope more broadly in Southeast Asia), may not be suffering from the dramatic population declines associated with the amphibian chytrid fungus in other parts of the world. This is incredibly good news, and we really hope that it’s true- but much more needs to be done before we are sure. Long-term population monitoring of frogs throughout Southeast Asia is needed, along with further work on the fungus itself.

Frogs are vital part of healthy ecosystems. It’s necessary to know what threats they are facing so that we can ensure they survive into the future. We hope that the amphibian chytrid fungus may be less of a threat to the amazing frogs of Southeast Asia than it is in other parts of the world.

Le Thi Thuy Duong
Faculty of Biology and Biotechnology, University of Science, Vietnam National University-HCMC

Hoang Duc Huy
Faculty of Biology and Biotechnology, University of Science, Vietnam National University-HCMC

Jodi Rowley
Curator of Amphibian & Reptile Conservation Biology, Australian Museum & UNSW.

More information:

• Le, D.T.T., Hoang, H.D., Rowley, J.J.L. (2017). Preliminary Monitoring of Amphibian Populations at a Montane Site in Vietnam with the Presence of Batrachochytrium dendrobatidis. Herpetological Review, 48(3) 557-559.