Julie is correct, but I read your first question differently. No dog can survive long (or with any QUALITY of life) if heartworm positive with adult heartworms clogging up the heart chambers. Any dog can be treated for heartworm but the more severe the infestation, the more difficult or dangerous the treatment can be.
In my rescue, we always treated dogs BEFORE adoption (because on rare occasions the dog CAN DIE and we do not want anybody to go thru that- on a newly adopted dog). We did have some of dogs have a BAD REACTION after the vet -given, treatment to KILL the adult worms. These dogs had to be rushed to an Emergency vet, when large numbers of DEAD heartworms began to affect the dog’s ability to breath, as they were being “shed out”. No way, should a new owner have to go through that terror (of hearing a dog struggling to breathe) or the EXPENSE thereof.
Yes, sometimes dogs who have only juvenile heartworms can be given the regular heartworm prevention and it PREVENTS them from maturing (or reproducing) & they are GRADUALLY shed out, but that can take UP TO A YEAR. At no time with any amount of heartworms can a dog be allowed to run freely or exercise as hard – as any healthy dog can. So while the normal heartworm prevention “treatment” can work on gradually getting rid of the juvenile version, we do not see it as a VIABLE or recommended way…. to get rid of them, unless the owner or rescue CANNOT afford the ($500 or more) speedy treatment for heartworms.
Dogs who are long infected with heartworms – BEFORE getting treatment, can have long-term heart damage – including dying sooner than normal, from congestive heart failure. (WE had that happen twice, to treated dogs). So some rescues weight that (since the would be adopters MAY have a shorter-lived dog) and do not place – but PUT DOWN dogs with adult heartworms, but it is a judgement call. If you have not talked to heartbroken families – who went through this, I do not think you can judge, this choice – NOT to treat but rather to euthanize (in some cases).
Puppies with umbilical hernias can easily be fixed with surgery at the same time as a spay or neuter, and that is USUALLY done; automatically. If adopting from an REPUTABLE shelter or rescue all animals should be FIXED prior to placement in a new home.
However, shelters may or MAY NOT check for heartworms & many ONLY test enough to clear them of ADULT heartworms (not the young juveniles) and shelters DO NOT normally absorb the cost of treatment BEFORE adoption….. so adopters NEED to BEWARE, of potential added costs.