# Study of Frog Disease May Benefit Human Medicine



## wmarkjones (Aug 31, 2010)

I came across a very interesting article today at Study of Frog Disease May Benefit Human Medicine : TreeHugger. The major emphasis in this article is on the Chytridiomycosis disease, otherwise known as the "Chytrid infection", which according to the article "is a disease caused by fungal infection and has been identified in amphibians around the world. Surveys have shown that as much as 30 percent of global amphibian populations have been affected and it is believed to be responsible for the extinction of more than 200 frog species."

One of the very interesting statements from this article was, "Now, new research has revealed that the key to survival [of the fungal disease] is population density: The fungus needs lots of hosts to infect and reinfect to continue growing, otherwise, it stabilizes." The intriguing aspect of this statement regarded the implication that the private care of low populations could possibly ensure survival of the species. That is, those caring for frogs personally, with the usual, commensurate low population densities, can actually be perpetuating the particular species being cared for by maintaining an environment that is naturally resistant to this fungal disease.

As a follow-on, one of the other intruiging questions posed in the article was suggested by the statement, "conservation efforts may be able to save susceptible frog species by preventing the disease from reaching this point." 

In your experience, how susceptible are your frogs to this disease? Also, if the susceptible species can be preserved by maintaining a low population density, what is that density breakpoint? Furthermore, since the article didn't provide specific information about population densities which coincided with the propagation of Chytridiomycosis, do you have any further information about such figures? Are we talking a population of 100? 50? 1000? And what is the radius of the population density referred to here? Finally, can you take practical measures to mitage the disease, such as splitting your populations between multiple tanks or other techniques, to avoid the problem of Chytrid infection?

My questions here arise from the lack of information in this article. I would enjoy hearing back from any of you that have more experience with this problem.

Thanks,

Mark


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## earthfrog (May 18, 2008)

Generally it is said that 'testing is too expensive' for individuals, to be used as an excuse for not doing chytrid testing on the frogs. 
This gives me an idea---someone, such as a vendor, could get supplies in bulk for chytrid testing and sell them individually to froggers so they could afford to test their collections themselves. I may do this myself and post the ad in the Supplies Classifieds. 

The idea of isolation in the prevention of the spread of chytrid is ideal but not currently feasible with the current management in this hobby in general. 
TWI is working on a chytrid-infection review of its own members, but this does not include the rest of the hobby in general. 
Thus we will continue to see valuable frogs lost due to often undetected chytrid within collections, and subsequent transmission to others through plant/frog trading.


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## edwardsatc (Feb 17, 2004)

The article from treehugger.com states:
“_Now, new research has revealed that the key to survival is population density: The fungus needs lots of hosts to infect and reinfect to continue growing, otherwise, it stabilizes_.”

The news article mischaracterizes the research. This statement leads one to believe that small or widely dispersed populations are at less risk. This research does not suggest this. In Vanderburgs journal article he states that “_Epidemiological theory generally suggests that pathogens will not cause host extinctions because the pathogen should fade out when the host population is driven below some threshold density_.”

Turns out that Vanderburgs research actually suggests that this is *not* the case. His results have shown that “_the high growth rate and virulence of Bd allow the near simultaneous infection and buildup of high infection intensities in all host individuals; subsequent *host population crashes therefore occur before Bd is limited by density-dependent factors*. Preventing infection intensities in host populations from reaching this threshold could provide an effective strategy to avoid the extinction of susceptible amphibian species in the wild_.”

As usual a journalist has totally misunderstood the research. Evidently he never read past the first line of the abstract. That’s why we should go to the source for science, not the news. The source in this case is:

Vance T. Vredenburg, Roland A. Knapp, Tate S. Tunstall, and Cheryl J. Briggs (2010) Dynamics of an emerging disease drive large-scale amphibian population extinctions. PNAS 107: 9689-9694

If anyone would like a copy, PM me with your email address.


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## wmarkjones (Aug 31, 2010)

edwardsatc said:


> The article from treehugger.com states:
> “_Now, new research has revealed that the key to survival is population density: The fungus needs lots of hosts to infect and reinfect to continue growing, otherwise, it stabilizes_.”
> 
> The news article mischaracterizes the research. This statement leads one to believe that small or widely dispersed populations are at less risk. This research does not suggest this. In Vanderburgs journal article he states that “_Epidemiological theory generally suggests that pathogens will not cause host extinctions because the pathogen should fade out when the host population is driven below some threshold density_.”
> ...


The abstract of the study you refer to is Dynamics of an emerging disease drive large-scale amphibian population extinctions ? PNAS. I would appreciate it if you refer me to a copy of the full study. You can either PM me or post it here as a PDF or weblink, if possible.

Thanks for the reference. I'll look at it further when I hear back from you.

I'm still interested in hearing from someone who has experience with this issue.

Mark


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## edwardsatc (Feb 17, 2004)

Here ya' go:

Dynamics of an emerging disease drive large-scale amphibian population extinctions ? PNAS


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