To put your mind at ease, it's highly unlikely that not cleaning the cage or the new puppy resulted in Speedy's death. Before I go into possible causes of death, i just want to mention that a hibernating hamster looks like a dead hamster. If your home was cooler than normal in the last 24 hours, that can be enough to send a hamster into hibernation. I know there's not much chance of this, but it does happen once in awhile. If that's a possibility, you could call your dad and have him try to warm up the hamster. As I said, this is only an outside chance, but I did want to mention it.
Without having a vet perform a necropsy, there is no way to know for certain what caused Speedy to die. There are, however, three likely causes. Because he died suddenly with no obvious symptoms, many conditions are ruled out.
Cardiomyopathy (a disease of the heart muscle itself, rather than a clogging of arteries) is inherited in some lines of hamsters. It seldom produces symptoms, resulting in sudden death when the heart just stops beating.
Salmonellosis is another possibility. This is caused by the salmonella bacteria. Hamsters can be afflicted by two forms of this illness. One form is long-term and has many symptoms. The other has a very sudden onset with a rapid death. This is a common cause of death when a hamster seems fine in the evening and is found dead in the morning. If you fed Speedy fresh vegetables and fruits from the grocery store without washing them, he could have contracted salmonellosis. You can read more about it here:
If you think salmonellosis is a possibility, it's very important to carefully disinfect everything associated with the hamster, and wash your hands thoroughly afterwards. It can be passed to humans.
Hamsters also can have strokes. A stroke often results in partial paralysis, but if severe enough, it can cause death. I suspect that Speedy died from one of the above three causes.
I feel bad for your poor son, and for you in having to break the news to him. If he would take some comfort in writing a little memorial for his hamster or reading comforting words such as the Rainbow Bridge story, you may want to help him use one of these free sites to do those things:
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