Unfortunaetly, TB has become increasingly common in zebra danios recently and this is almost certainly the cause of your fish's deformity. I'm sorry to say that the few times I have encountered it the only solution was euthanasia. Other symptoms include swimming with a slant, with the head constantly upwards, the fish losing weight or not growing and lethargy including slow swimming and periods of 'resting' on plants and gravel (in fish like danios this is unnatural). Unfotunately, the symptoms will vary widely and the only certain symptom is the one your fish is displaying. You should isolate him and you can try to treat him with some antibiotics but it may or may not help. I would actualy think it kinder to eauthanise him as he will only be suffering.
I doubt the cause of the fish's condition is genetic though inbreeding can make fish more succeptible to disease. The same upplies to old age.
Though it can be transmitted to humans, it is not the TB that humans normaly get and is not deadly. It can infect you if it gets into open wounds or the like and will cause painful swelling but can be easily treated. Still, keep your hands out of the water as much as possible and you should where elbow-length gloves. Also remember that your other fish could easily contract it (not just zebra danios) and that the disease may be present in your tank long after the infected fish is removed. Some people will even say it's always present but only appears when a fish is weakened by stress, old age or bad water quality etc.
