Written by Andrew Smart, Head of Science & Research
A recent publication by Rebecca Clemons and colleagues has found a DNA virus in strains of Bd, the fungus that causes chytridiomycosis.
Bd is one of the fungal pathogens that cause the disease chytridiomycosis in amphibians, resulting in skin infections that can led to mortality. Bd is associated with declines and some extinctions in over 500 amphibian species.
One of the factors contributing to panzootic (global infectious disease outbreak) expansion is ‘escape’ from fungal enemies such as viruses. Many fungi are reduced in virulence by mycoviruses (viruses infecting fungi) which are ‘hyperparasites’ (parasites of parasites), some of which are RNA viruses and some single-stranded DNA viruses. The research team screened various strains of Bd to look for evidence of DNA viruses and discovered they occurred in all of the five strains examined but at high, medium and low frequencies; the lowest by far being the global panzootic strain.
The mycovirus was named BdDV-1 and experiments found that strains with the mycovirus had reduced fungal growth rates in laboratory culture conditions. However, further experimental work with live fungal hosts found that there was significantly higher mortality rate in frogs (dwarf clawed frogs Hymenochirus boettgeri were used) infected by the Bd strain containing the mycovirus. Conversely, animals that died from the Bd mycovirus positive strain shed a lower number of zoospores (infective fungal life stages) than those infected by Bd without the mycovirus.
This variation in results based on laboratory growth and virulence in live animals warrants further investigation, but this first identification of a mycovirus in Bd may lead to long-term developments that could influence the impact of Bd on amphibians. However, there is also a risk that hybridization between Bd strains could increase the virulence of existing global panzootic strains. Initial work by Clemons and colleagues also found that Bsal, another cause of chytridiomycosis, did not show evidence of these DNA viruses, so we must continue to be vigilant and do our best to maintain biosecurity and avoid spreading infection where we can.
You can read the full paper here.