Chytrid Fungus Background

Chytrid, chytrid, chytrid ... all you ever hear about is chytrid!

Over the past few years, there has been a LOT of publicity in the media about frog declines and, in particular, the role that disease has had in causing many species to decline and even disappear entirely. However, the overwhelming majority of attention thus far has been focused on the relatively recently discovered "chytrid fungus" (Batrachochytrium dendrobatidis for the scientifically inclined). Chytrid (pronounced KIT-trid) fungus is indeed a serious disease and it causes massive dieoffs where it occurs - but it is not the only disease which has been causing deaths in North Queensland and other parts of the globe.

a 2,000 times magnification of a chytrid fungus zoosphore

When people find a sick frog, they assume that it must have the chytrid fungus because of the publicity. The reality is that, for most frog species, the fungus itself is extremely hard to detect without the aid of a powerful microscope. Some of the symptoms it causes might be seen in some frogs - usually a pink or red flush on the inside of the thighs and the belly and a brown, granular sloughing on the bottom of the body - but not others, especially in the early stages.

A possible sign of chytrid outbreak is simply that many dead or nearly-dead frogs are found in a specific area during a time of year when daytime temperatures are consistently under 27 degrees celsius. Another indication is that frogs and toads will spend exhorbitant amounts of time soaking in water and will be found in ponds, etc. during the daytime. (Mass dieoffs can also be caused by someone spraying herbicides or other chemicals so the frogs will still need to be tested by a pathology lab or seen by an experienced disease researcher to determine if disease or poisoning is responsible.)

Even though there has been funding directed towards the study of chytrid fungus, there is still a lot that we don't know about this deadly fungus. Perhaps this might change now that chytrid fungus has officially been designated as a Key Threatening Process by the Australian government and some funding has finally been directed to pure research. In the meantime, the answers to these questions are still elusive:

  • Where did chytrid fungus come from? We know that worldwide, there are about 80 species of chytrid fungus which feed on algae, plant material, keratin (skin), etc. but why did the amphibian chytrid come to be toxic to frogs and tadpoles - did it mutate from another chytrid? - Was it altered by environmental conditions (pollution or increased UV) to become toxic? There are some who are convinced that chytrid came from Africa with shipments of Xenopus but this has been called into question by the International Society for Infectious Diseases.
  • How does chytrid kill amphibians? (Does it interfere with their hydrology? Does it produce a mycotoxin which is attacking their nervous system? Does it poison them? Does it alone kill the frog or does it cause something else to happen which kills the frog? Frogs are being concurrently attacked by many other pathogens which are considered "opportunistic" [meaning that these pathogens go around looking for vulnerable life forms to attack] so does that mean that frogs are being wiped out by diseases (any disease which happens a lot of the time to be chytrid) because they have become weakened immune systems?) There are also some who believe that chytrid kills by upsetting the osmotic balance in the body causing the heart to stop. Again, this is being debated. It is the personal view of this author based on cases she has seen that chytrid produces a mycotoxin once it has migrated through the skin, and this mycotoxin attacks the nervous system - slowing it down until all nervous system "communication" in the body is ceased. It would be great if this line of inquiry was persued to either prove it or dispute it !
  • Why doesn't chytrid kill all the frogs in a specific area? (In rainforest areas, stream-dwelling frogs are most affected by chytrid but other frogs which would use the stream are not affected.) Would this be a score on the "opportunistic pathogen" side of the board instead of the "emerging pathogen" side of the board chytrid is currently tacked onto?
  • Has chytrid fungus always been around but not 'active' all the time, or: has it come from somewhere else and is being spread by something such as another host, weather patterns, people, etc.? (While the prevailing view of delegates to the August 2000 international conference on amphibian disease in Cairns was that chytrid is a new disease which is being spread, it remains a controversial question and not all delegates agreed on this aspect. It is important which answer is true because we will find it difficult to devise containment and minimisation procedures if we don't know how the disease is related to environmental and other conditions.)

We also have two other pages in this site concerning the recognition and treatment of chytrid. Our hands-on experience with live cases of chytrid has been limited by our locally tropical climate which has discouraged chytrid from establishing here, but chytrid has finally arrived in Cairns as of 2005 and we have received our first case in May 2006. The information we present in our recognition and treatment pages is based on the treatment of a very limited number of cases and our procedures DO work. If we learn any techniques in the future which are more efficient, we will certainly post them.

 

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