Chytrid fungus

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[edit] About Chytrid Fungus

Chytrid Fungus (KIT-rid) (Batrachochytrium sp.) is an epizootic and a major contributor to the decline of amphibian populations around the world, threatening many species with extinction.

This fungus is a global emerging amphibian pathogen which is proving to be one of the worst vertebrate infectious diseases found so far. It is causing a huge amount of extinction and disease within amphibian populations.

More than 100 species of amphibians are known to be affected by the chytrid fungus (Batrachochytrium dendrobatidis). Some are very susceptible and die quickly while others which are more resistant are carriers of the pathogen. The disease, called Chytridiomycosis, is already credited with wiping out frogs and toads in large numbers in Australia and South America.

The aquarium hobby's main two species available from shops are the Dwarf African Frog (Hymenochirus boettgeri) and the African Clawed Frog (Xenopus laevis). These have shown to be infected in retail aquarium shops in the USA and Canada. Whilst so far it is only present in wild frogs in the UK amongst other countries.

During the 1950s African Clawed Frogs, which are carriers of this fungus, were breed in their thousands to be pregnancy tests for women across the world and this is perhaps one cause of the wide spread of this fungi as many of these frogs got released in the wild.

After the 1990s the African clawed frog (ACF) became a popular domestic pet throughout USA, Canada and Europe. Since the ACF is a carrier of this fungi and doesn't appear to die from it, it is easy for the fungus to have infected the owners tanks and perhaps the surrounding garden by the incorrect disposal of the tank water during water changes which will carry the fungi into the local streams so introducing the fungus to wild amphibians.

Since 2005 there are been many reported cases of people in the USA and Canada purchasing one of more dwarf african frogs only to have all their pet frogs die within 2 months (the average killing period of the fungi) in various Yahoo pet frog groups and web site forums. It is believed that shop personal, both large and small, are transmitting the fungi between tanks due to bad hygiene care or ignorance.

Most pet shops have so far, proved less than willing to do any positive preventative measures with their stock. So the onus is on the purchaser to ask questions.

  • When buying an amphibian, ask if the animal has been treated for the fungi or has been quarantined for at least 2 months. This applies equally to captive bred or wild caught animals.
  • Carefully check the shop to see if untreated African clawed frogs are also being sold. Shop assistants can transfer infected water droplets between tanks.
  • If buying untreated african clawed frogs, ensure all waste water is disinfected before disposal to kill the fungus and so prevent the possibility of it spreading to the local wildlife.


[edit] Symptoms

When an amphibian is seen to be infected, the skin becomes dry, pale and similar to how a frog looks just before a shed of its skin. It has been noticed that Dwarf African Frogs (DAFs) seem to try to leave the water several days before their death. It is believed this may be due to lack of oxygen (frogs breath through their skin) due to skin damage. It is estimated that 90% of animals will die if left untreated.

  • The infected amphibian will pass on the fungus to all other amphibians in the tank.


[edit] Treatment

Malachite Green, Formalin and Copper sulphate reduced the percentage of deaths. With the most effective chemical being Benzalkonium chloride. One online forum has posted details of this fungus and has developed an experimental quarantine treatment for infected dwarf african frogs. See Flippers And Fins for details.

A Betadine (Povidone 10% iodine) bath (1:100 diluted) is quoted on the FDR Project web site. See link below.

  • Increasing the oxygen content of the tank and lowering the water level to a few cms so the animal doesn't have to swim very far to reach air is also recommended.**

Since the main cause of death appears to be the massive electrolyte imbalance caused by the fungus. It is prudent to add a 1% dilution of the following salts to the treatment tank to aid the animal in replacing these lost minerals.

  • 6.0g NaCl - Sodium chloride
  • 0.5g KCl - Potassium chloride
  • 0.25g CaCl2 - Calcium chloride
  • 0.25g Magnesium chloride
  • 7g of domestic unrefined Sea Salt is an acceptable substitute of the above salts.
  • 1 litre dH2O - distilled water

ie if you have a 10 litre tank add 100ml of this.

  • Since the fungus develops slower at higher temperatures the fungus growth can be slowed by increasing the tank temperature to around 28-30°C (82.4-86°F) . Dwarf African Frogs come from areas of Africa where the ground temperature is easily this high.


[edit] Chloramphenicol Treatment

In Early November 2007 a new experimental cure treatment for CF was announced. The PDF detailing the treatment can be found here. At this time, this has not been tried yet on the dwarf African frog and a starting dose of 10ppm is recommended.

  • PDF file (Chloramphenicol cures chytridiomycosis) can be found from nzfrogs.org. Or see here.
  • If people trying this drug could discuss their results on the discussion page at the top of the page, this would be appreciated. --Quatermass 15:34, 4 November 2007 (CST)

[edit] Quarantine

Keep the animal at the lower end of its temperature range. This allows the fungi to develop more rapidly and therefore you can be sure it is not present if you quarantine for 2 months. Otherwise add an extra month to be sure.


[edit] Temperature

  • It is said that the fungus stops reproducing above 32°C (89.6°F) and dies within 6 hours out of water.
  • The fungus also dies if the temperature rises above 35°C (95°F) for more than 6 hours.


[edit] Killing the fungus in your aquarium

  • Remove the animals and treat them separately.
  • Remove any plants and throw them away. They will not survive the high temperature.
  • Remove any fish and keep they away from the frogs for at least 2 months (the fungi can live in the water without the frogs for around 7 weeks).

Thoroughly dry out the aquarium, all the ornaments and all equipment for at least 12 hours. Start the countdown from the last droplet of water to go. The fungi can't live in the dry.

Alternatively heat up the aquarium water slowly (to prevent the glass cracking) to at least 40°C (104°F) and the fungi will die within 6 hours if you maintain this temperature.

[edit] Links

  • Amphibian Ark - Chytrid fungus and chytridiomycosis with an article on field-Sampling Protocol for Batrachochytrium dendrobatidis from living amphibians, using alcohol preserved swabs.
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