I just got my girl back from a 3 day stay at the vet. Thought I'd share a little of my experience as a word of warning to my fellow Jack owners.
Gracie is an active (duh) healthy four year old terrier girl. She's current on all her shots, and isn't regularly exposed to other dogs. I do have two cats, but they are indoors. Early Wednesday morning, I awoke to sounds of Gracie throwing up. I didn't pay too much attention because I was mostly asleep, and kind of thought I was dreaming. When I got up around 7 a.m., I walked into the living room and was greeted with puddles of bloody vomit. Not tiny puddles, either. Total carnage. I freaked out. The cats were acting normal, but Gracie was not. She's a picky eater sometimes, so it didn't raise any flags when she hadn't eaten much of her food for the previous week. But now, I realized I should have paid better attention. Also, I hadn't really paid attention to whether or not she was going to the bathroom. I usually let her out, she does her thing, barks at stuff, and then comes back in when she's finished. She was listless and I had to carry her outside. When I got her leash, she just leaned on me and didn't jump around like she usually does. I called the vet and they had me bring her in.
I had to drop her off, because I had to get to work. The vet called me a few hours later and said it looked like
Hemorrhagic Gastroenteritis. They aren't really sure the causes, but it's common in little dog breeds, and young adult dogs. They put her on IVs and antibiotics, and it took a couple of days, but she recovered. She's a little thinner now, but you have NO IDEA how glad I am to have her home.
So anyway...keep an eye on your doggies, and trust your instincts. If you think they're acting abnormally, you're probably right.