This disease has been prevalent for a long time and it seems to be getting worse and worse. For the longest time, it was virtually non existent where I live and now, it seems that more and more dogs here are testing positive for heartworm disease.
The next time you go to your vet, have your dog tested. Some of the signs and symptoms of this disease are very subtle (inflammation internally, tired, out of breath easily while playing, lethargic,etc), some are not so subtle. It’s best to get them tested and to be on top of things. If they have the disease and it is caught early, there are simple treatments and it can be reversed. If not caught early, the prognosis is usually grim.
Please have a look at this article and get your dog tested. It can be the difference between a healthy life and an early death.