You’re thinking about the old drug, an arsenical(?) that had to be injected IV. The current recommended therapies, considered SOPs, include the only currently approved adulticidal drug, melorsamine dihydrochloride (or Immiticide). While it is still no walk on the park, it is MUCH LESS dangerous than the older drug. If, by any chance, you see a vet suggesting the old old method, run like hell the opposite way and get a new vet ASAP.
The current, most common preventive medications are all macrocylic lactones. Some resistance and breakthrough heartworm have been reported. The good thing is, though, if the owner can show proof of current heartworm prevention, the drug company usually will foot all or at least part of the treatment.
There are different reasons why it may be on the rise. It may have always been there, but not been diagnosed. Unlike canine tests, which can detect the antigen, feline tests detect just the antibody. And they are not very reliable. And sometimes, due to the parasite biology and life cycle in cats, there is no antigen to be detected.
So many cases could have been misdiagnosed, mismanaged, or simply missed. Also, many cats present DEAD, and if the owners/veterinarians do a necropsy, then they find the cat had worms. If they hadn’t done one, they wouldn’t have known.
I have never given my 3 dogs or two indoor cats the preventative medication (or flea medication for anyone but my flea-allergic Tibetan Terrier, or regular vaccinations). To me it’s not worth the cost and possible side-effects, short and long term, and the risk is acceptable. I do get the dogs tested for heartworm at their (infrequent) check-ups. I’m not a big believer in doctors for myself, and I think most of the current veterinary recommendations for dogs are a load of BS. Some vets (and doctors) support my various opinions and conspiracy theories, but certainly not the majority.
I prefer to spend my money on non-drug preventative measures, for all of us: optimal nutrition, exercise, and plenty of sunshine (vitamin d!). My older dogs are now 13 and 10 and in great health, not an issue between them.
I live in Philadelphia, incidence is relatively low here. If I was in an area with more risk I would put the dogs on Heartgard.
Different breeds of dog have different kinds of appetite. So it’s possible that the pills you give to your dog might not be suitable to it. Do not try to do any kind of experiment with your dog’s appetite, it can be harmful to it.