 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.
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? The earliest cases of chytrid in museum specimens are in Xenopus,
the African Clawed frog, from way back in the 1930's.
- 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 attacked by many
other pathogens which are considered "opportunistic" [meaning
that these pathogens go around looking for weak 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 worldwide by something we can't see in the environment?)
- 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.)
- 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 recommend you visit
the Amphibian
Disease website at James Cook University. This is a comprehensive
site covering what we currently know about chytrid fungus as well as records
of all frogs and tadpoles in Australia and overseas which have tested
positive to chytrid.
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 suspected
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. As
we receive more cases this winter and continually refine our observations,
we will edit these pages to reflect the best knowledge we acquire about
this very serious disease problem.
Last edited: May 14th, 2006
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