Prevention is the only weapon in the fight against heartworms


WITH ABOUT 60 species of mosquitoes ready to deal your dog a death sentence with one bite, prevention is the only weapon you have.

The killer heartworm is transmitted from dog to dog only by the mosquito. And, once your pet is infected with heartworm, it will eventually die unless a very painful and expensive treatment can effect a cure. Often it cannot.

Your pet should be tested by your veterinarian to be sure it does not have heartworm, and then should be put on preventive medicine. Giving a dog preventive medicine without knowing it is free of heartworm can be fatal.

It is never too late to begin the prevention, according to veterinarian Eddie Molesworth at the Main Street Veterinary Hospital on Reisterstown Road.

"Some owners give preventive medicine all year because it is easier to keep going, and also they know their animal is protected," he says. "Otherwise it should be started before the onset of the mosquito season and given until approximately two to three weeks after the first frost."

People cannot get heartworm from the mosquito, nor can they get it from an animal. It is predominant in dogs and has been reported in cats.

Molesworth says "the incidence has not increased. We see fewer cases than in the past because of awareness through client education." The highest incidence is in stray animals.

The journey of the heartworm is a cycle, starting anew when a mosquito bites an infected dog. Immature heartworms in the infected dog's bloodstream will not mature in that dog, but must be processed first by the mosquito. When it bites, the mosquito takes in some of the larvae. Over a period of about two weeks, they develop to the infective stage while in the mosquito's body. When the mosquito bites again, it deposits some of the larvae. It takes this infective larvae a month or longer to migrate to the dog's heart and lung area and begin to mature.

One dog can have 20 or more worms, nine to 14 inches long, within its pulmonary vessels, causing shortness of breath, loss of weight, listlessness, coughing and eventually convulsions and death. When a dog reaches this stage of infection, a cure is virtually impossible.

It is possible for a dog to have heartworms that aren't reproducing. Also, the dog may have a very strong immune response with antibodies that kill off the immature heartworms but cannot kill the adults. Veterinarians call this hidden heartworm; if they suspect it has occurred, they'll do further testing.

Cats are incidental hosts and seldom test positive, so a veterinarian looks for signs of hidden heartworm. "I've never had a cat with heartworm although it is reported in cats as far north as Vermont," says Molesworth. "With heartworm, cats have more of a pulmonary than a heart problem," he adds.

Anywhere there is a mosquito and one dog infected with heartworm, the chance of giving every dog in the area heartworm disease is great.

A test can determine whether immature heartworms are in the dog's bloodstream. Giving a dog medicine that kills heartworm larvae is the only way to prevent the infection. In the early stages of heartworm, an arsenic derivative can be used to kill the worms in the dog's body. If it works, the recuperation period after treatment is crucial.

As the worms die from the arsenic, they crowd into the heart chamber. And they stay there until absorbed into the dog's body. The dog must be kept very quiet for many weeks, until the worms are completely absorbed. With even slight exercise, the dog can have severe respiratory problems and die.

So, if you own and love a dog or cat, have it tested and begin heartworm preventive medicine, which can be administered by a monthly pill or a daily one. Ask your veterinarian.

Copyright © 2020, The Baltimore Sun, a Baltimore Sun Media Group publication | Place an Ad