Is Animal Testing (for Medical Purposes) Ethically Acceptable or Not?

[sun rise]

As for the animals, some commonly used species in certain fields are rats, guinea pigs, dogs, and monkeys

And so I'd amend my prior statement to include the choice of the least conscious animal possible.

What would you designate a "serious disease"? Is there a specific threshold beyond which a disease qualifies for such a designation?

I'm not an ethicist who has thought about this in detail. One thought though is whether or not there's a current treatment and the research is designed so that a business can patent a new drug for the same issue or not. Other criteria could be how widespread the disease is, how much suffering and death it causes, the odds that the research will find a cure and so forth.