cause of rats death?

Question
QUESTION: I raised this baby roof rat until he was about nine months old or so.  I took excellent care of him - I built a giant cage for him and fed him fresh veg/grain/fruit every day along with the complete nutrition rodent blocks, and he got lots of daily attention and roam-around time.  He turned out to be a very sweet, affectionate pet.

And he seemed perfectly healthy until about a week ago or so.  His behavior/energy/appetite didn't change except for two things.  First, he was slightly less fastidious than normal about grooming his back end - occasionally we'd find poops hanging off the fur there (normal poops).  Second, he developed a bald patch in his back.  The skin underneath looked pretty normal (not lumpy, red, weepy, or scaly at all) except for a tiny little scab near the center of it.  We never saw him grooming or scratching the bald spot.  It appeared last week while I was out of town (my live-in boyfriend was in charge).

Today I came downstairs and found him dead.  He was lying across the ceramic plate we use to feed him - it looked like he was relaxing on a hot day or something (it isn't hot here now, though) with his head resting on the plate.  He had no external injuries.  But there was some blood in his mouth and nose - no blood in the surrounding area, though, so it wasn't profuse bleeding.

The only other thing I can think of is stress.  He had been antagonizing (squeaking/hissing at) the domestic rat we got him as a companion (when the roof rat was about 5 months old) for some time.  They never fought enough to draw blood, but we could tell they were never going to be good friends, and just yesterday we decided to find another home for the domestic rat and posted an ad on craigslist.  So this was a source of stress for the roof rat - his aggression had gradually escalated since the domestic rat reached sexual maturity.  But the blood in his nose and mouth makes me think that it wasn't stress that (alone) killed him.

I know that without an autopsy there's no way to be sure what the cause of death was.  But I thought you might have some ideas about possibilities.  Thanks for your time and effort.

ANSWER: That bald spot with the scab in the center was probably ringworm. That's what it sounds like to me. It may have been brought on by stress (stress lowered his immunities enough to allow him to contract ringworm) or he may have had it for months and you never would have known. I'm guessing he got it from the new rat you put in with him - its very easily contracted from animal to animal, and can be spread to humans, too.

You kept the roof rat with the domestic for 4 months before deciding they would never be friends? I'm surprised it took you so long. Most people give up within a week or two. Fact of the matter is, wild rats and domestic rats will ALWAYS hate each other. I know people who have raised orphaned roof rats in litters with their fancies and had the roof rats grow up to argue/fight/hiss and display aggression at their adoptive siblings. In the future if you decide to get a rat a buddy it should be done before puberty hits (5 to 8 months) in males; the younger you introduce them, the easier they'll get along. Also, you should always introduce the older, existing male to a much younger male, to prevent arguing. And domestic rats should NOT be housed with wild rats.

Who knows, for sure, what was going on with that particular strain of roof rat line. Maybe 9 months was old age to them.. maybe they have rampant cancer or his mother was a sickly rat herself, thus why he was orphaned to begin with. He may have had underlying respiratory problems or, most likely, heart problems (rats are very prone to heart disease). It's hard to tell given he had absolutely no symptoms. I'm very sorry for your loss, either way. You did wonderful by raising him, to begin with! Most people wouldn't, and those who try rarely succeed.

---------- FOLLOW-UP ----------

QUESTION: Thanks for taking the time to answer me; I really appreciate it.  I know that it's not uncommon for rats to die suddenly, but it's the blood in his mouth and nose that has me wondering about the cause.  Would a heart attack/failure explain it?  I guess it's a possibility that the blood was from another, related problem.  The roof rat was a runt to begin with and runts usually have health problems, so I may never really know.

Just so you know, the two rats were friends at first.  The domestic rat was about 5-6 weeks old when we introduced them, and the roof rat was about 5 months old.  We had been trying for months to find a baby male domestic in our area (we didn't want to buy one from a pet store) because of exactly what you said about puberty.  The roof rat started antagonizing the domestic a couple of months later, so the fighting had really only been going on for 1-2 months before we decided to separate them.

Answer
Heart disease usually displays with cyanotic feet and tails (blue skin), and I've seen a few bleed from the nose in such a fashion, though usually its trauma or lung failure that causes excessive bleeding from both the nose and mouth. Lung failure normally is a gradual thing and can be caused by chronic infection (which you said wasn't likely, as he hadn't been sick) or cancer. I know cancer is very very common in domestics but I'm not sure about wilds.. I would imagine it would be, but I honestly don't know the facts about cancer in a wild population.