The primary cause of red-leg is poor husbandry. Make sure that the terrarium is clean, the right temperature, avoid overcrowding, fecal matter removed, and any water in the terrarium must be clean and conditioned properly. The cause is a gram-negative bacteria Aeromonas and is characterized by reddish hemorrhages on the inner thigh. It is very serious and spreads quickly to other frogs. It is nearly 100% fatal unless treated properly in its early stages (it spreads so rapidly that there can be considerable damage to the internal organs before it manifests itself). Pseudomonas, Proteus, Citrobacter, Salmonella, and Escherichia coli can also contribute to the infection. Much easier to prevent than cure.