Chytrid: a Deadly Fungus Threatens Endangered Amphibians
The chytrid fungus, whose scientific name is Batrachochytrium dendrobatidis (Bd), is decimating amphibian populations worldwide, especially in Central America and Australia. The fungus has contributed to the extinction of nine frog species native to Australia and almost 200 species worldwide. When B. dendrobatidis affects a community, up to a 50% morbidity rate is seen in the native amphibian population and 80% of the affected animals will die within a one year period (mortality rate). It is believed that the fungus was originally found in South Africa and has spread throughout the world by the transportation of amphibians for food and for the pet industry.
The fungus causes the skin of the infected amphibian to thicken, thereby interfering with the ability of the animal to absorb water and electrolytes. It is believed that the resulting electrolyte imbalance seen in frogs sends them into a fatal cardiac arrest. Electrolyte transport across the epidermis, or skin, of the frog results in depletion of potassium levels by up to 50% and plasma sodium by 20%, thereby disrupting the heart’s rhythm.
Symptoms of infection include difficulties in the balance of the infected frog (ataxia), problems in motor skills, convulsions, and paralysis.
The PCR test is the most reliable means of detecting chytrid infections in both wild and captive amphibians and is the only technique capable of accurately quantifying the number of B. dendrobatidis zoospores present on skin swabs. In the United States, PCR testing is available through Pisces Molecular in Boulder, Colorado at (303)546-9400.
Although there is as yet no cure for the chytrid fungus, researchers have found that giving affected amphibians drugs to restore electrolyte imbalances slightly prolongs the lives of animals infected by the fungus.
The chytrid is even a sporadic problem in world-wide zoo collections and with species reintroduction programs. The fungus is known to wipe out local populations-some of which are threatened already.
Steps which can be taken to prevent the introduction of the chytrid fungus include: testing of newly purchased animals, quarantine of new arrivals, practicing good hygiene when handling different animals (e.g. disposable gloves), and never mixing populations. Ideally, new animals should be PCR tested twice, 6 weeks apart. The fungus can be killed with a 1% bleach solution or by heating surfaces to 120°F for 30 minutes.
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Nolen, R. “New Guidelines Intended to Guard Amphibians against Deadly Fungus.” JAVMA Vol. 234, No. 8 news. P.1000.