Basically fish TB is a bacterial infection in humans that comes from a bacteria that infect fish (the technical term is zoonosis). As Bob said, a common sign of this disease is a sore on your hand that wont go away, and most peoples infections do not progress beyond this. However there have been cases in the UK and the US where people have lost limbs due to the infection, but this is extremely rare. The infection is carried by fish and aquarists come into contact with the bacteria when they put their hands in the tank during maintainence. Its even possible to get mouth infections if you suck start your hoses when siphoning out your tanks. You can avoid getting the infection by following simple hygiene such as washing your hands after touching your fish tanks or coming into contact with the water in your fish tanks, avoiding suck starting hoses, wearing gloves during maintainence, not putting your hands in the tank if you have open sores or other wounds, ect. Given this disease appears to come from fish only, this may be another reason to go with that shrimp only tank you've been dreaming of! With a proper diagnosis, fish TB is generally readily treated with antibiotics. However most common antibiotics used to treat infections often don't treat this bacteria, so the right antibiotic has to be used. So if you have a wound that won't heal, remind your doctor that you keep fish and asked to be tested for fish TB. As Bob also said, this is something to be aware of but not to freak out over.