Historical Evidence of Widespread Chytrid Infection in North American Amphibian Populations

Abstract

Emerging infectious diseases may be contributing to the global decline of amphibian populations. In particular, chytridiomycosis, a cutaneous fungal infection of amphibians caused by the chytrid Batrachochytrium dendrobatidis, gained attention in the 1990s as an apparently new pathogen. This fungus has been implicated as the causative agent of widespread mortalities among wild amphibians in geographically disparate parts of the world. To investigate the global distribution, historical occurrence, and infectiousness of this pathogen, we examined 3371 postmetamorphic and adult amphibians collected between 1895 and 2001 from 25 countries for the presence of chytrid fungi in the epidermis. Cutaneous chytrid infection was diagnosed in 383 of 2931 (13.1%) specimens of 12 common amphibian species from five Canadian provinces and seven American states, including 30 of 69 locations examined in the St. Lawrence River Valley of Québec. Chytrids were observed in 7.0% (46/655) of the adults collected in the 1960s, the earliest cases being two green frogs ( Rana clamitans) collected in 1961 from Saint-Pierre-de-Wakefield, Québec. In recent studies, morbidity and mortality attributable to chytridiomycosis were not observed in infected amphibians from Québec despite a 17.8% (302/1698) prevalence of chytrid infection during the period 1990-2001. The prevalence of infection during this latter period was not statistically different when compared with the period 1960-1969. Epidermal chytrid infections were not observed in 440 amphibians examined from 23 other countries. In light of the fact that infection by B. dendrobatidis is widely distributed and apparently enzootic in seemingly healthy amphibians from eastern North America, lethal outbreaks of chytridiomycosis among amphibian populations appear to have complex causes and may be the result of underlying predisposing factors. Resumen: Las enfermedades infecciosas emergentes pueden estar contribuyendo a la declinación global de poblaciones de anfibios. En particular, la quitridiomicosis, una infección fungosa cutánea en anfibios provocada por el quitridio Batrachochytrium dendrobatidis, atrajo la atención en la década de 1990 como un patógeno aparentemente nuevo. Este hongo ha sido implicado como el agente causal de extensas mortalidades en anfibios silvestres en sitios geográficamente dispares en el mundo. Para investigar la distribución global, la ocurrencia histórica y el nivel infeccioso de este patógeno, examinamos a 3371 anfibios postmetamórficos y adultos, recolectados entre 1895 y 2001 en 25 países, para detectar la presencia de hongos quitridios en la epidermis. Diagnosticamos quitridiomicosis cutánea en 383 de 2931 (13.1%) de especimenes de especies comunes de anfibios de cinco provincias Canadienses y siete estados de E. U. A., incluyendo 30 de 69 1432 Chytrid Infection in Wild Amphibians Ouellet et al. examinadas en el Valle del Río San Lorenzo de Québec. Observamos quitridios en 7.0% (46/655) de los adultos recolectados en la década de 1960, los primeros casos corresp...

Predicted Disease Susceptibility in a Panamanian Amphibian Assemblage Based on Skin Peptide Defenses

“…A preserved R. pipiens from Colorado, 1974, represents the earliest known infection of that species (Carey et al, 1999), and recent studies found infected frogs in apparently healthy wild populations (Green et al, 2002). Historic evidence suggests that B. dendrobatidis is enzootic in R. pipiens (Ouellet et al, 2005). The strength of X. laevis resistance is consistent with a coevolutionary history with the fungus.…”

“…Only two Panamanian species, C. prosoblepon and P. lemur, were predicted to be more resistant than North American R. pipiens, which survives infection with B. dendrobatidis (Ouellet et al, 2005). MALDI MS indicated that potentially novel antimicrobial peptides are present in the skin-peptide mixtures of C. prosoblepon.…”

“…Survival of natural populations of R. pipiens and X. laevis infected with B. dendrobatidis (Green et al, 2002;Weldon et al, 2004;Ouellet et al 2005) and resistance to experimental exposure (Rollins-Smith and Conlon, 2005;Carey, unpubl. data) demonstrate that these species are quite resistant to disease development.…”

Host invasion by Batrachochytrium dendrobatidis: fungal and epidermal ultrastructure in model anurans

“…We build on existing reports of Bd thallus ultrastructure (Berger et al 1998, Davidson et al 2003, Ouellet et al 2005, Simoncelli et al. 2005, Une et al 2008) by providing TEM micrographs of Bd in bullfrogs and wood frogs and, to our knowledge, the first account of the host invasion process in any host species.…”

“…We build on existing reports of Bd thallus ultrastructure (Berger et al 1998, Davidson et al 2003, Ouellet et al 2005, Simoncelli et al 2005, Une et al 2008) by providing TEM micrographs of Bd in bullfrogs and wood frogs and, to our knowledge, the first account of the host invasion process in any host species. Host invasion by Bd parallels that in other exogenous chytrid fungi and ap pears morphologically similar in experimentally infected bullfrogs and wood frogs, species that display disparate levels of mortality risk for chytridiomycosis.…”