pet mices mysterious death

Question
My daughter loves her 4 pet mice she bought from a pet store last July. They were the ones people bought to feed their snakes with.  She cares for them and takes care of them daily, she takes them out and handle them lovingly often.  Recently, one of the mice seemed to have a lump on the back.  A few weeks later, it died suddenly.  Even the night before it seemed active and normal.  This morning, another one seemed to have a lump on his back, but even last night it seemed normal and happy.  Tonight, we noticed it lay in the same spot for hours.  My daughter took it out gently and put it in a box with the bedding and all, and kept it in her room to watch it closely. It started to eat a little when my daughter crumbled the food and gave it to the little one, but it won't drink at all.  It lay there quietly.  An hour later, it seemed to have a spasm and kicked wildly, and died. It was still well last night, it's hard to believe or understand what have happened? It's real sad, each time. I don't want to bother you with the details about how attached my daughter is to them, (she is 18 years and going to college this fall).  We don't' have a clue what's happening. Is there a contagious disease that is spread among them? We don't want to loose another one. Would you help us to know what might be going on?  Oh, about 2 weeks ago, we found this little one have dendrites on the back fur. Other than that, nothing unusual.  The 4 lived nicely, occasionally we hear/saw them fight a bit, but never serious. They don't injure each other.  Thank you for your time and help.

Answer
Hi!

A mysterious lump would suggest a tumour, which is very probable, unfortunately, for a 10-month old mouse. These tend to be highly hereditary, and people who breed mice to serve as snake-food often do not care much for the health of the mice themselves.

It's rare albeit possible for a mouse to die of the indirect effects of a tumour overnight, and this would suggest that the kind of tumour-type this litter has inherited is a very aggressive kind, possibly near the spine itself?

I know it may sound silly to most people - but purchasing mice from actual breeders is a much better option than petstores. Locating a local mouse breeder is a whole other matter though! :-)

Unfortunately there's nothing to be done in case of a tumour but to take the pet to the vet to be put to sleep. I can most definitely relate to the sadness caused by a pet's departure, and wish you two strenght! I hope the remaining two will live a long, tumourless life. Best of luck!