Some stuff in the article I can't agree or disagree with as I can find no other appropriate articles with a quick internet research. I have other resources at home with access to veterinary papers.
I disagree with a lot of what it says though, and you're misinterpreting it incorrectly as well.
Most mosquito species in American are appropriate hosts. The three main species I mentioned before that are often active in winter months once it's above 50 degrees all can pass on HW. Aedes communis, Culiseta inornata, and Anopheles freeborni are all capable of carrying microfilaria and passing them on and are all known to be active once the weather hits 50 degrees. These are all species found in the northern US as well. I can't speak as to temperature maturation for microfilaria, but from speaking with my vet on tonight she feels that as long as the mosquito is active, there is the chance to spread it on, but I simply do not know that one.
You mention FEMALE mosquitos, which makes you think that half the mosquitoes that bite you are male. But that is the article you posted trying to pull the wool over your eyes and make it seem less like a threat, vs. yes I agree some websites that make it seem super scary. I bet you didn't know that it's simply females that carry the microfilaria because females are the only gender that feed on blood? Males do not bite anything. They feed on flower nectar. So of course only female mosquitos transmit HW.
Once the microfilaria is in the blood stream of a dog (or cat), they do not need a further bite from a mosquito to mature into adults. It takes roughly 6 months for the microfilaria to mature into adults, but they need no further outside help once they are in the blood. While the microfilaria is in the bloodstream they cause no harm, but once they mature into adults in the heart they can cause severe damage. Yes eventually if new microfilaria are not introduced into the blood stream, the adult heartworms will die off but this can take years, and there can be infestations with hundreds. Again, the only reliable test only detects female ADULTS already in the heart. So damage is already being done.
I would not say a dog with a strong immune system can fight them off, because I've seen plenty of young "healthy" dogs with HW disease, one was a 4 year old german shepherd we treated for 8 months before it still eventually died.
My biggest pet peeve is when everyone accuses vets pushing stuff for the money. Frankly, vets don't make a lot of money. Yes, there are some out there, but for the most part, vets simply follow their education to offer you the best option they feel for your pet. I feel the biggest reason vets push for year round is NOT because of making money, but the opposite, to avoid lawsuits. Owners sue or take you to the boards over EVERYTHING. If a vet didnt recommend you do year round heartworm, and then your dog gets HW in December (rare but I think it could definitely happen), then who are you going to blame?
Vets have to protect outliers. Yes, most dogs will NOT get HW in December. Most mosquitos are dead or hibernating. But a lot of mosquitos hibernate in basements and crawl spaces and what not IN buildings. I don't know about you, but my house never gets below 68 degrees in the winter. There are minor possibilities, yes I agree minor, but still possibilities that dogs could get infected in "winter" months (BTW I checked NY records, every single day in December, January, and February, the 3 coldest months in NY, had record highs in the 60s and 70s, so it could happen. Freak warm front). Vets HAVE to recommend it in the freak possibility that your dog is the rare outlier that gets infected with HW in December.
Not only that, but the common practice of shipping dogs all over the world for "rescues" is a large cause of infestation. Colorado, where I live, NEVER use to have fleas, we NEVER had HW. We did, but minor cases. Now, increased temperatures combined with lots of dogs from out of state (we got a TON of dogs in after hurricane katrina), we see a LOT more cases. Just last year I saw 3 different dogs diagnosed HW positive at my day practice within 1 week, which was VERY unusual and a high number. 1 was a geriatric lab, the other two were middle age dogs.
I don't tell people to do stuff because I could make money off it. In fact I'm very anti-a lot of common stuff in the field. I feed raw, for example. But I recommend the same thing I would do for my own dogs, because I am very educated in veterinary medicine, and I see first hand the consequences of NOT following those recommendations. 1 year old unvaccinated dogs dying of distemper, I've seen it. 4 year old german shepherds dying of heartworm, I've seen it.
ANY article that starts off on a 3 paragraph tangent about how everything we do is just to take your money, I'm not going to take seriously. Because it's offensive. And it's ridiculous. There are horrible vets out there. But there are more good ones. And I think most would recommend it.
Don't give HW if you dont want to, it's your choice. Don't fool yourself into thinking "early" detection is going to do anything though, because "early" detection is still adult infestation in the heart, but your right to make your own calls. And don't blame vets for just following industry standards in preventative medicine.