Discovery of chytridiomycosis in New Zealand
Bruce Waldman1, Vera Andjic2, Phil Bishop3, John Klena2, and Richard Norman4.
1 Department of Zoology, University of Canterbury, Christchurch, New Zealand;
2 Department of Plant and Microbial Sciences, University of Canterbury, Christchurch, New Zealand;
3 Department of Zoology, University of Otago, Dunedin, New Zealand;
4 Institute of Veterinary, Animal & Biomedical Sciences, Massey University, Palmerston North, New Zealand.
We found evidence of morbidity and mortality in a natural population of bell frogs, Litoria raniformis, during regular monitoring of a pond in Canterbury, New Zealand, during spring and summer 1999/2000. Within a two-week period, we found 5 lethargic frogs and 11 fresh carcasses. The lethargic frogs demonstrated unusual posture and failed to flee upon approach during daylight hours. All but one of the sick frogs died in the laboratory within 24 hours. Organisms resembling the chytrid fungus Batrachochytrium dendrobatidis were identified in histological sections of skin from the affected frogs but not from apparently healthy frogs collected from the pond during this period. Microscopic skin lesions varied in appearance, typically with only the most superficial epidermal cells colonised by zoosporangia. Despite intensive monitoring, no additional morbidity or mortality was detected among the hundreds of adults remaining in the pond. However, as the pond began to dry up, large numbers of sick metamorphosing tadpoles were discovered. Symptoms included skin ulcerations, internal bleeding, and body swellings. Around the pond, many dead and dying metamorphs were found under rocks. Histological sections of metamorphs revealed infection by chytrids. Pseudomonas, Aeromonas, and other still unidentified alpha-hemolytic bacteria were cultured from tadpoles. Because the pond serves as a source of animals for the pet trade, chytrid fungus may be inadvertently being spread throughout New Zealand and possibly overseas. We now have identified incidents of chytrid infection and mortality of metamorphs at several Canterbury localities in which translocations of tadpoles are known to have occurred from the initially identified pond. Bell frogs were originally introduced into New Zealand from Australia approximately 100 years ago. The vulnerability of rare and unique New Zealand native frogs (genus Leiopelma) to chytrid fungus is still unknown.