Bearded Dragon illness

Question
My brother bought a female bearded dragon that was a golden brown color, about 1 year old and maybe 6 inches long. He read books and websites and made sure the cage size, temperature, water, terrain, food, etc were all what they were said to be. After about 3 weeks the lizard turned completely black, began to vomit, and diarrhea, listlessness and died. This all happened within about 24 hours.
My mother and I were thinking that maybe the lizard came with a disease or maybe she ate a diseased mouse. Can you help us with any other ideas of what may have happened?
Thank you very much for your time.

Answer
Hi Kyla

That must have been terribly shocking and traumatic for your brother and family. Unfortunately it would be pure speculation for me (or even a reptile veterinarian) to try to guess at what may have caused that death. They symptoms you mentioned are not specific to any one disease or condition. You mentioned that the dragon was about a year old at the time but also said that it was 6 inches long. If that was the total length (including tail) and not just the body length then it was severely under sized for its age as well. A one year old dragon, even a female, would normally be over a foot long in total length. That would certainly suggest that it was likely not well and had not been thriving before your family acquired it.
I'm not clear from your post whether the dragon was eating and appeared otherwise healthy in the 3 weeks prior to its death. Most illnesses (infections, intestinal parasites) and conditions like intestinal impaction that affect beardeds do not have the rapid onset of symptoms that you described. They tend to  progress more slowly with days of lethargic behaviour, closed eyes and lack of appetite. I should mention that fireflies are one thing that will kill a bearded quite quickly, just in case your brother fed her insects from outside. Fireflies possess a toxin that beardeds and some other repitles are quite susceptible to.
Mouse colonies can sometimes harbour Salmonella but reptiles are not affected with the same enteric symptoms that this bacteria causes in humans. I doubt the mice were involved.

I hope this experience has not turned your family off the idea of beardeds altogether.