Frog fungus damages immune system even when eliminated

Sunday, 14 September, 2014

The amphibian chytrid fungus, Batrachochytrium dendribatidis (Bd), has a significant effect on the immune system of Australian tree frogs even after the fungus has been cleared. Dr Sam Young, a veterinarian at Mogo Zoo, NSW,, led the research team at James Cook University's One Health Group (Young et al 2014). Her work demonstrated that experimentally infecting green tree frogs (Litoria caerulea) caused multiple defects in systemic host immunity with both antibody and cell mediated immune fuctions affected.

Even more surprisingly a frog species that is able to control and eliminate experimental infections with Bd showed long lasting blood changes suggesting immune damage. The white lipped tree frog, Litoria infrafrenate, (see image) eliminated the experimental challenge, but had lower white blood cell and serum globulin concentrations in recovered frogs compared with unexposed frogs

Bd has been responsible for a pandemic in amphibians that has now spread across the globe, resulting in massive loss of amphibians from pristine and other areas and extinctions of species. Understanding how Bd kills amphibians has been complex since the fungus is only superficial in the top layer of the epidermis. Rick Speare, THS Director and one of the co-authors of Dr Young's paper, was a key member of the team that identified the amphibian chytrid fungus as the cause of global amphibian declines (Berger et al 1999) and made major advances in understanding how frogs with chytridiomycosis die (Voyles et al 2009).

Sam Young's work adds to the slowly developing picture of the complex pathophysiological effects of such a superficial fungus.

Berger L Speare R, Daszak P, Green ED, Cunningham AA, Goggin CL, Slocombe R, Ragan MA, Hyattt AD, McDonald KR, Hines HB, Lips KR, Marantelli G, Parkes H. Chytridiomycosis causes amphibian mortality associated with population declines in the rainforests of Australia and Central America. Proceedings of National Academy of Science 1998;95:9031-9036.

Voyles J, Young S, Berger L, Campbell C, Voyles WF, Dinudom A, Cook D, Webb R, Alford RA, Skerratt LF, Speare R. Pathogenesis of chytridiomycosis, a cause of catastrophic amphibian declines. Science 2009;326(5952):582-585.

Young S, Whitehorn P, Berger L, Skerratt LF, Speare R, Garland S, Webb R. Defects in host immune function in tree frogs with chronic chytridiomycosis. PLoS One 2014; e107284. doi:10.1371/journal.pone.0107284

Image: A white lipped tree frog at the Getting the Jump on Amphibian Disease! Workshop and Conference in Cairns, December 2000. Dr Ken Aplin is the frog's companion.