# Cure for chytrid?



## ccc (Nov 22, 2006)

interesting article:

http://news.bbc.co.uk/2/hi/science/nature/7067613.stm


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## Julio (Oct 8, 2007)

very intersting, thanks for hte article.


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## jess (Sep 10, 2007)

still, i'm skeptical. itraconizole can also be used to cure captive amphibians of the disease. the article implies that frogs that are treated are then "resistant" to chytrid, but there's no follow-up support for that statement. 

if it truly does make a frog resistant to chytrid after reintroduction, that would be awesome, but it's still unrealistic as a solution to the global issue.

i'm very interested to see the peer-review scientific article that comes from this.


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## Ed (Sep 19, 2004)

I would wait to see the actual article in print and for follow up work to be done on it for the following reasons, 

the media release touts it as first making the frog's resistant and then stating it cures it. These are two totally different things. The second reason is because chloroamphenicol has until that article no known activity against any fungi (it is even used in yeast cultures to suppress bacterial growth) so it is an odd choice to start trying to cure fungal infections in any case. 

The third thing is that even if the frogs were rendered resistant or cured, it does not solve the problem where chyrid is in the enviroment as it is incrediably unlikely that the offspring of the frogs would also be resistant.... 

Ed


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## bbrock (May 20, 2004)

Ditto to Jess and Ed. I too think we need to wait for the peer-reviewed pub to draw any real conclusions. It is an interesting development, but I'm not so sure about "breakthrough".


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## rozdaboff (Feb 27, 2005)

It will be an interesting read when (and if) it is published.

Like Ed mentioned, the mechanism of action of chloramphenicol has not been shown to affect fungi previously (it blocks bacterial protein synthesis). However, in reading the BBC article, they are only using live animals as their experimental groups - not culture techniques. It is possible that the chloramphenicol is working on the commensal bacteria of the frogs - which allows a less prevalent bacterial species unaffected by the chloramphenicol to colonize the frogs. It is then the presence of this bacteria that affects the chytrid, either by outcompeting it or by producing a product that affects chytrid.


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## Ed (Sep 19, 2004)

At least in one caudate species (Plethodon cinereus) there are bacteria that can outcompete chytrid.. But I would like to see the information directly. 
(and if it does enable a different bacteria to colonize and outcompete the chytrid, this change in bacterial flora may be a temporary item, which would mean that the frogs could be susceptiable later...) 

Ed


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## sbreland (May 4, 2006)

I wouldn't be so worried about the fact that chloramphenicol has never shown any effects on fungus before... one of the mysteries of medicine is how a seemingly unrelated medication will have unexplainable effects in an application that was never thought possible. It happens all the time in human medicine... why not here? 
One thing I drew from the article and how it could relate in a global sense is that IF it does make them more resistant, they were talking about reintroducing captive bred species to the wild. Previously they have done that but the releases have all just died within a few years due to lack of resistance. If the claims are true, it sounds like they think that they could release captive treated populations to the wild and they would have more resistance then, giving them a better chance at survival. I do agree though that the article leaves a lot to the imagination and that the journal needs to be seen first, and that this doesn't really address existing wild populations (unless you go out and collect them and treat them and then re-release them... now you're talkin big $$$$$). Still though, I look at this as any good news is a start.


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## bbrock (May 20, 2004)

Ed said:


> At least in one caudate species (Plethodon cinereus) there are bacteria that can outcompete chytrid.. But I would like to see the information directly.
> (and if it does enable a different bacteria to colonize and outcompete the chytrid, this change in bacterial flora may be a temporary item, which would mean that the frogs could be susceptiable later...)
> 
> Ed


But if this does turn out to be the case, it would be a substantial leap forward in our knowledge of how to counter chytrid. In the short term, it may provide a tool to pre-treat released animals so they don't immediately succumb to the fungus. Or perhaps it could buy the animals time enough to survive exposure to chytrid that leads to natural immunity. But this is all conjecture at this point and we can only hope. I do think that the probiotic approach has offered the greatest hope yet.


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## rozdaboff (Feb 27, 2005)

sbreland said:


> I wouldn't be so worried about the fact that chloramphenicol has never shown any effects on fungus before... one of the mysteries of medicine is how a seemingly unrelated medication will have unexplainable effects in an application that was never thought possible. It happens all the time in human medicine... why not here?


While it is a possibility Stace, it is highly unlikely. For many drugs currently in use - we know that they work, but don't always know the mechanism of action. However, the mechanism of chloramphenicol is understood for the most part. The drug targets an enzyme (peptidyl transferase) that is essential in bacterial protein synthesis by binding to the 50s subunit of the bacterial ribosome (prokaryotes have 50s and 30s ribosomal subunits). Fungi, as eukaryotes, have very different ribosomes (consisting of 60s and 40s subunits), and the drug can't bind. That is why many antimicrobials are so effective against bacteria, but have limited effects in the patient being treated with the drug. If chloramphenicol were able to bind and inhibit - this would not only likely be seen in many other types of fungi, but also higher eukaryotes.

Furthermore, by performing the experiments with animals and not in culture, there are numerous other variables that can't be controlled for - which is why any claim of direct action of chloramphenicol against chytrid must be taken with a grain of salt. However, this is a great example of why culture type experiments, which control for most other variables, are often limited in their power, as they cannot include the interactions of many effects at the level of the organism.


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## bbrock (May 20, 2004)

sbreland said:


> One thing I drew from the article and how it could relate in a global sense is that IF it does make them more resistant, they were talking about reintroducing captive bred species to the wild. Previously they have done that but the releases have all just died within a few years due to lack of resistance. If the claims are true, it sounds like they think that they could release captive treated populations to the wild and they would have more resistance then, giving them a better chance at survival.


But even in the article they state they have no clue how this resistance is working. It could be simply that by treating the fungus, the frog's immune system reacts to the fungus and the treatment simply allows the frog to survive - giving the immune system a chance to develop immunity. That could be good and bad. Bad, because it would still require frogs to be exposed to chytrid to become "resistant". Which means captive frogs would have to be exposed to chytrid, then treated for the fungus, prior to release. And then their offspring would just as likely die from the fungus in the next generation. But it could also make it easy to develop an attenuated strain of the fungus that could be sprayed in the environment. That would expose wild frogs to an asymptomatic form of the fungus, allow them to develop natural immunity, and then more likely survive exposure to the more virulent strain. So there could yet be some neat stuff come out of this work. I just don't think it is time to declare a "breakthrough" just yet.


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## Ed (Sep 19, 2004)

You also need to keep in mind that amphibians during metamorphosis undergo a period of fairly severe immunosuppression (theorized to prevent the larval lymphocytes from reacting to adult tissue antigens) and this could be a strong indicator of why remnant populations of infected anurans may not have any recruitments as up to 100% of the infected tadpoles may die. 

Also being resistant is not necessarily a good thing as the tadpoles are resistant to chytrid infection but it can significantly affect thier growth and size at metamorphosis (see http://www.ingentaconnect.com/content/k ... awler=true ). 

Ed


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## bbrock (May 20, 2004)

Ed said:


> You also need to keep in mind that amphibians during metamorphosis undergo a period of fairly severe immunosuppression (theorized to prevent the larval lymphocytes from reacting to adult tissue antigens) and this could be a strong indicator of why remnant populations of infected anurans may not have any recruitments as up to 100% of the infected tadpoles may die.
> 
> Also being resistant is not necessarily a good thing as the tadpoles are resistant to chytrid infection but it can significantly affect thier growth and size at metamorphosis (see http://www.ingentaconnect.com/content/k ... awler=true ).
> 
> Ed


Yet another paper I'd like to get my hands on. I really miss access to a research library.

But I'm not sure you can chalk this up to resistance per se. Yeah, the tadpoles weren't killed, but they still had to battle the disease apparently. If they were resistant prior to exposure, those effects may not have occured. But you are right that this shows just how many hurdles still need to be jumped.


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## Ed (Sep 19, 2004)

Hi Brent,

I can dig out other references.. the general consensus is that other some mouth part deformations in some species tadpoles have little in the way of direct mortality from chytrid. (Depending on the species, tadpoles tend to have less keratin that adult frogs which is why chytrid doesn't seem to kill them. For an interesting abstract see http://abstracts.co.allenpress.com/pweb ... /?ID=27470 

Ed


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