Not Much Room for a Mouse 

D. E. Larsen, DVM

We had several clients who always wanted to talk with me rather than the front desk. That was on the phone or in person. They were always men, and for the most part, they were large animal clients.

They were accommodated if my time allowed for the conversation. These guys didn’t abuse their status in the clinic, and they were always willing to wait their turn or call back if it was a phone call.

So, when I noticed Bill standing aside out in the reception room, I knew he was waiting to speak with me.

As soon as I had a spare moment, I stepped out to the reception room and motioned Bill to come back. He followed me to the surgery room. It was the only open room we had at the time.

Bill was one of my favorite large animal clients. His cow herd was not large, but it was well cared for, and I often visited his place. If he needed a dog looked at, he would send it in with his wife. He had cats on his farm, but I think they were like the barn cats of my youth. They were pretty much on their own.

Bill was a tough man. He had been in the Marines during World War Two and fought in the Pacific. Bill was on Iwo Jima. And he even had similarities in his appearance to Lee Marvin.

“Now, Doc, I don’t want you to be laughing at me,” Bill said as he laid a small towel down on the surgery table. “And I didn’t kill this little guy. I would have, had I found it alive, but I found it dead.”

I carefully unwrapped the towel. It seemed like I could remember almost the same conversation with Bill a year or two ago.

There in the towel was a dead mouse. And a pitiful-looking little mouse.

“I have never seen anything like this before,” Bill said. “You always seem to have all the answers. It is sort of like nature is sending me stuff to see if I can stump you, one of these days.”

I pulled on a pair of exam gloves and picked up the little mouse. On closer exam, the skin was moving. I parted the fur, and there was a breathing hole. I turned the mouse on its back. There were four large lumps on his ventral abdomen. Then I found three similar masses on each side and two on his back.

“Bill, did you ever see any warbles on your cow’s back?” I asked. “I mean, we treat them now, but twenty years ago, warbles were common.”

“Yes, I used to squeeze them when I was a kid,” Bill said. “The biggest grub you could imagine would pop out of those warbles.”

“Do you see all these lumps on this mouse?” I asked. 

“Yes, that is why I brought him in for you to look at,” Bill said. “You know, I have a bunch of grandkids. I don’t want them exposed to anything from some sick mouse or squirrel.”

“Well, if you watch these lumps, they move,” I said. “The mouse is dead, but these lumps are still alive. These are like those big grubs you popped out of those warbles on the back of a cow.”

“These are from heel flies?” Bill asked.

“No, it is a different fly, but sort of the same type of life cycle,” I said. “These are Cuterebra larva. They are from a rodent bot fly. We see them in rabbits and occasionally a cat. In those animals, they are a nuisance. In this little mouse, there is not much room for a mouse. It is all larva.”

“So, nothing to worry about for grandkids,” Bill said.

“Probably not,” I said. “I have seen a note or two about these on people, but I would guess that is pretty rare. Especially if you bathe once in a while. Probably the biggest risk would be for one of the little ones finding a mouse like this and picking it up while it is still alive.”

“If I just left this mouse out in the barn, would those things go ahead and hatch?” Bill asked.

“I think the flies didn’t read the book very well,” I said. “If a parasite that kills the host, generally it kills itself. There are so many larvae in this mouse; he has just been consumed. In a few days, these larvae will be dead.”

“Do you want me to dispose of this guy?” Bill asked.

“No, my garbage can is as good as your manure pile,” I said. “I can get rid of the mouse. And there are a couple of gals here who need to see him. So they can know what people are talking about next time we get a call.”

“How many times to see something like this?” Bill asked.

“Bill, I have never seen one of these larvae on a mouse before,” I said. “I see two or three cats every year with one of these. It is a big circus to pull the larva out, especially if we have a curious client who wants to watch.”

“Okay, you can throw the towel away also,” Bill said. “Billie as was definite that she didn’t want me to bring that back to the house.”

“That’s good. I will just put the whole thing into the trash can,” I said.

“Do I owe you anything?” Bill asked.

“No, I will get out of you on my next call,” I said.

Photo by Alexas Fotos from Pexels