Leopardess said:
Well yes, if your fish are sick and you stick open wounds into the tank you may just be asking for it. My point was not to scare people off and have them freaked out about simply cleaning their tank. You have the same odds, presumably, of catching the disease any time you go swimming anywhere...its not as if fish tanks are the "cause" of it. Re: the cess pool comment, that is true, but Earth is also a closed system, whose water supply must also support the wastes and needs of every animal on it, aquatic or not

But we're digressing here quite a bit
We are digressing here quite a bit here and I dont want to sound like I am going for an argument, I am not.

I am not trying to scare people and maybe this informayion dose not belong here, if so I appologise. But you talk of the earth being a closed system, I agree and so I assume you are refering to our fish tanks as closed systems which I totaly disagree with.You speak as though our tanks are holding only a lttle more bio-load than what the earth supports,eg. even if you kept one neon tetra in a 1000g tank that would still not come close to bio-load/water volume that the rivers and lakes are supporting(taking into account terrestrial animals). If you are not calling our tanks closed systems then you must agree that higher bio-load means more wastes and more wastes mean more disease. So in actual fact I am saying that the fish we keep in our tanks can be, under certain circumstances ,more prone to disease which translates into more risk for us. So yes I believe that you are more likley to be affected if you have sick fish and you have cuts on your hand, that being said M marinum is an uncommon infection. In the United States, studies report an approximate annual incidence of 0.27 confirmed cases per 100,000 patients ,so it is very unlikely that you will be infected by this.
This however is very concerning. This is an extract from this web page.
"Over the pass decade it would appear that mycobacteriosis (Fish Tuberculosis) has slowly developed a stranglehold on the rainbowfish hobby in Australia. Information from international sources would indicate that it is also commonplace among rainbowfishes in both Europe and North America. I believe that it is now so widely circulated in the hobby that it is almost impossible not to be beset by it at some time. In fact, it may be bordering on an epidemic. Most cases of mycobacteriosis are not reported or more often, are simply misdiagnosed. Mycobacterial infections of fish can only be confirmed by positive laboratory findings. " This is a scary thing ,most of M marinum cases are not reported or misdiagnosed and can only be indentified through scientic methods. This could mean that one of us may have already had this disease in our tanks. And let me ask you this if you knew you fish were infected by this and you had an open wound on your hand would you knowingly put your hand in the water? I know I wouldn't.
http://members.optushome.com.au/chelmon/Myco.htm
Don't you agree that this information should be passed around, and not informing people just because it may scare some of them is no reason to not pass it around.
But I will say again
dont panic ,it is very unlikely that you will be affected, that being said if your fish are sick I would show a little caution putting your hands in the water if they have cuts on them.
Btw I have always put my bare hands in my tank and I will continue doing so, in fact as ergo sum said in his post with big tanks sometimes you have to get inside them to clean them and my tank is no exception.