How does such a thing happen?

This little dog came to me Monday, having never seen a veterinarian in her life.
And she’s 10 years old.
And her fecal flotation is negative for intestinal parasites.
And her heartworm test is negative.
It seems so amazing as to be impossible, but it’s true.
Granted, she will have to have
another heartworm test in six months before she’s out of the woods. Still, don’t you find it pretty amazing that a dog can live in the Deep South, where mosquitos are thick and heartworms abound, and not (yet) suffer from that parasite?
There is only one explanation: the immune system.
There is no doubt that Mindy Sue has been bitten by mosquitos in her ten years of life, and that some of those mosquitos were carrying heartworms. Somehow, during the process of larval stages injected by the mosquito maturing through the various phases, the little dog’s immune system “zapped” them before they could proceed to become adult worms.
Don’t think this is a reason to not give your pet heartworm preventive! Dogs can and do die from heartworm disease all the time if their heartworm infestation is not detected early enough.
And, as we’ve said recently, with Immiticide heartworm treatment medication currently being unavailable, it’s a bad time to skip heartworm preventive doses, or even be late with them. Editor’s Note: As of December, 2011, Immiticide was again available through Merial’s European source.
See you tomorrow, Dr. Randolph.