Action: Immunize amphibians against chytridiomycosis infection
- One randomized, replicated, controlled study in the USA found that vaccinating mountain yellow-legged frogs with formalin-killed chytrid fungus did not significantly reduce chytridiomycosis infection rate or mortality.
Chytridiomycosis infection often spreads rapidly once it has been introduced to amphibian populations, causing mass mortality and population declines. However, some species of amphibians appear to be resistant to developing the disease if they have previously been exposed to the chytrid fungus Batrachochytrium dendrobatidis (Hanselmann et al. 2004). This suggests that it may be possible to reduce infection by injecting animals with dead chytrid fungus to stimulate a protective immune response.
Hanselmann R., Rodríguez A., Lampo M., Fajardo-Ramos L., Aguirre A.A., Kilpatrick A.M., Rodríguez J. & Daszak P. (2004) Presence of an emerging pathogen in introduced bullfrogs Rana catesbeiana in Venezuela. Biological Conservation, 120, 115–119.
Supporting evidence from individual studies
A randomized, replicated, controlled study in a laboratory at the University of California, USA (Stice & Briggs 2010) found that vaccinating mountain yellow-legged frogs Rana muscosa with formalin-killed chytrid fungus did not significantly reduce infection rate with chytridiomycosis or mortality. The proportion of frogs that became infected (chytrid/adjuvant: 0.8; adjuvant only: 0.9; control: 0.8) and died (chytrid/adjuvant: 0.4; adjuvant: 0.4; control: 0.2) were similar to controls. Following vaccination, there was no significant difference in the time to infection, rate of increase in chytrid zoospores in animals (chytrid/adjuvant: 0.08; adjuvant: 0.08; control: 0.09) or the maximum number of zoospores per frog (chytrid/adjuvant: 53,990; adjuvant: 17,831; control: 5,106). Frogs were randomly assigned into three groups of 19–20 individuals. Controls received an injection of saline. One group received a 1:1 vaccination of formalin-killed chytrid fungus in Freund’s complete adjuvant (to increase effectiveness) and one month later formalin-killed chytrid in Freund’s incomplete adjuvant. Another group received saline with Freund’s complete adjuvant and one month later saline with Freund’s incomplete adjuvant. Injections comprised 0.05 cm³ into the dorsal lymph sac. Frogs were exposed to live chytrid (105 zoospores) one month after treatments. Individuals were monitored weekly for chytridiomycosis using swabs of the ventral surface.