Give the next regularly-scheduled dose. Once a dog gets infected, it takes seven months for that infestation to mature. Keep giving your regular heartworm preventative as directed, and then, seven months later, get another test. And if it's negative, great, your dog is probably fine.

We can. Vector control or mosquito control is probably the most important. Mosquitoes breed in standing water, so try to eliminate standing water in your area. Flower pots can be a source of water for them to replicate in. Also, there are certain high feeding times for mosquitoes—morning is one, and then at dusk. Avoid having your dog hanging out outside during those times, and it might decrease your dog's risk of mosquito bites. However, that alone is not a preventative.

Even dogs in the house get infected with heartworm. Mosquitoes can get in the house and bite your dog and inject five to 10 baby worms into your dog.

No, there are none that we would recommend. In dogs with heartworms and baby worms circulating in their blood, some of these heartworm preventatives are not appropriate in that situation, as dogs can have an allergic reaction if they have baby worms circulating in the blood with certain products. We avoid those products in the initial treatment of a positive dog because of that.

An occasional dog can have diarrhea, but it’s very rare. And with some of the topical products, the products placed on the skin, you have an occasional dog sensitive to the carrier or whatever it is in that topical product. That dog might have some itching and hair loss in that area. Again, that's pretty rare, though. These products are safe for the Collie breeds. You'll read about that sometimes, and people worry about that. Sometimes, Collies have trouble with certain medications, but these products are all very safe.

The heartworm preventatives are 95% effective, if not more. There are a few cases of resistant heartworms that have become more recent. They used to be 100% effective. Now, they're about 95%, I would say. And that's still pretty good.

Also, some people are under the misconception that they don't have to give preventives in the winter. That's not true. Especially here in North Carolina, we have temperatures where mosquitoes can replicate and infect dogs all year. We recommend year-round treatment in most places in the United States now.

There are many products out there. They're called macrocyclic lactones, that's the class of medication, and they're very safe monthly pills. And many of them treat intestinal parasites as well. There's also an injection called ProHeart. There's ProHeart 6 and ProHeart 12 for people that have trouble remembering to get pills monthly. And there are topical products—Advantage Multi and Revolution are a couple of them out there that we apply topically to kill the worms. Many of these products are also effective against intestinal parasites, and some of them are combined with flea and tick products. The product we choose depends on the individual dog's lifestyle and the owner's needs.

In the cases of advanced heartworm stages, where the dog is in heart failure or has portacaval syndrome, a terrible complication dogs can get with heartworms; we treat those dogs differently. They need to have their heart failure treated, and sometimes, they require surgical removal of those worms, and it carries a very poor prognosis.