Chytrid fungus

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About Chytrid Fungus

Chytrid Fungus (KIT-rid) (Batrachochytrium sp. - Batrachochytrium dendrobatidis) is a fungal pathogen 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 bred in the 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 have 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.

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.


How does it kill?

The fungus consumes the Keratin in the amphibian's skin, the skin is afected and grows thicker therefore inhibiting the animals ability to breath through its skin and to regulate its internal electrolytes.

The build up of electrolyte salts such a potassium and sodium in the body is now believed to stop the heart.[1]

It takes around 2–3 months for a typical infected frog to die from this fungus. The speed of the infection varies with temperature as the fungus prefers cooler temperatures to grow.

Treatment

There a several known working treatments available to the home frog owner.

Terbinafine Hydrochloride and the Heat treatment are the most commonly used.


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.

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.

7g of domestic unrefined Sea Salt is an acceptable substitute of the above salts.

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


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.

Due to serious human health concerns associated with Chloramphenicol, it was banned for use in aquarium fish in the United States. Contact your physician prior to attempting this treatment. [1]

Terbinafine Hydrochloride Treatment

LamisilATspray.jpg

The commonly available over the counter liquid spray form of human foot fungus treatment 'Lamisil AT' (Terbinafine Hydrochloride) has been discovered to be successful in treating amphibians.[2]

Treatment is as follows:
Buy Lamisil AT Athlete's Foot Spray Pump (1% Terbinafine Hydrochloride). This is available in the USA, Canada and UK.

Put 10 squirts into 200ml of water. Soak frog for 5 minutes per day for 10 days, being sure to have solution get onto the entire frog. Keep the frog in a clean set up after each treatment as putting it back into the original tank will just keep reinfecting the frog. Sterilize and redo the original set up and any instruments that may have come in contact with the frog or its water before reintroduction of the frog. Best to wear disposable plastic gloves and swap them after frog is inserted into treatment area.

Heat treatment

By heating the water holding the frog to 32°C (89.6°F) for the minimum period of four days (96 hours) the fungus and its spores are known to die.[3]


Place the frog into a small tank of about 15-20 Litres (4-5.3 US G.) and find a heater that can be set to warm the water to a steady 33-34°C (91.4-93.2°F) (it may help to insulate the tank sides and bottom with a towel). Provide water circulation to aid oxygenation of the water as warm water holds less.

It is not recommended to use a air pump with hose and an air stone as this is pumping 'cold' air into the water and will be a potential haven for the Chytrid fungus to survive.

Dechlorinate the water.

Provide a overhead light to the tank as this will help heat the water surface area and overhanging air to at least 33-34°C (91.4-93.2°F) .

Use an accurate thermometer, preferably one with a minimum/maximum temperature memory to record the minimum temperature the water gets to. Place the sensor as far away from the heater as possible.

Add a 1% solution of sea salt to the water to aid the frog's recovery.

Adjust temperature of the tank to current temperature of the water holding the frog and introduce the frog.

Slowly over a six hour period increase the temperature of the heater until you get to the target temperature.

If the frog is mature (at least one year old) and well sized, do not feed during the five days. If the frog is very young or is looking slim then a single light feed every two days can be done. But ensure any waste droppings from the frog are removed and monitor the water for ammonia levels. At these high temperatures any level of detected ammonia is more lethal (see Ammonia toxicity). Using a daily ammonia removing treatment bottle may be prudent.

It has been observed that the frog will be less active than normal. But whether this is due to the high temperature or the stress of the new environment is unknown.

After the five days, slowly lower the temperature back down to a more normal 25°C (77°F) over another six hour period.

Latest News on treatment of Chytrid Fungus

In March 2009, Professor Reid Harris published papers (Skin microbes on frogs prevent morbidity and mortality caused by a lethal skin fungus. ISME Journal, in press, doi:10.1038/ismej.2009.27. and Addition of antifungal skin bacteria to salamanders ameliorates the effects of chytridiomycosis. Diseases of Aquatic Organisms 83:11-16.) on the use of a common bacteria Janthinobacterium lividum which appears to kill the pathogen if present on the skin of the amphibian in sufficient numbers. After applying this bacterium to infected tree frogs it did indeed kill the fungus.

More on this research which started in 2006 - A Silver Bullet?

The bacteria appears to be used in Universities as a teaching aid, so perhaps the bacteria could be obtained and sold to Pet amphibian owners? Perhaps a Walstad tank constructed with this bacterium would cure infected Dwarf African Frogs in America and Canada? --Quatermass 10:02, 21 June 2009 (UTC)

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.

Temperature


Killing the fungus in your aquarium

method one

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. However, this will likely kill any plants you have in it.

method two

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 an arid climate.

method three

Lastly remove all amphibians from aquarium, vacuum substrate and leave aquarium without amphibians for ~3 months. The fungus needs Keratin to survive and without this it will eventually starve.[4]

method four

To ensure equipment is clear of CF, you must dry out the equipment.
Once all moisture is gone do a countdown of at least three hours and and CF spores should all be dead.[3]

Links

References

  1. BBC - Secrets of frog killer laid bare. Science 23 October 2009: Vol. 326. no. 5952, pp. 507 - 508. Article: Life and Death Play Out on the Skins of Frogs by Elizabeth Pennisi
  2. The Frog.org web site March 2008 by Steven Busch
  3. 3.0 3.1 Johnson PDF paper - Fungicidal effects of chemical disinfectants, UV light, desiccation and heat on the amphibian chytrid Batrachochytrium dendrobatidis
  4. Johnson ML, Speare R. Survival of Batrachochytrium dendrobatidis in water: quarantine and disease control implications. 2003 Aug
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