When to Start a Heartworm Preventative

Heartworm is a parasitic worm that lives off the infected host. Dogs and cats are most commonly infected with heartworm through the bite of a mosquito. The larvae grow inside the bitten animal over a period of three months as they migrate to the heart. Adult heartworms reproduce and obstruct the heart's chambers and blood vessels. Other organs can can also be damaged, eventually leading to death if untreated.

  1. Prevention

    • Heartworm can and should be prevented. Before you start your pets on a program, have them tested for worms and then tested again periodically after that. Once tested, your vet may put your pet on a monthly prevention program, such as Heartgard or Sentinel.

      There are a variety of options for prevention, including daily or monthly chew tablets, topical medications and now a six-month shot that is available only for dogs. These medications kill the larvae before they can grow into adult worms.

      For success, administer heartworm medication as instructed. Consistency is the key to success in prevention. Some vets recommend that animals be on a prevention program all year, because the medicine also prevents other parasites. Others believe using the medication during mosquito season is sufficient.

    When to Start

    • Start heartworm prevention with puppies as young as four weeks old and kittens at six weeks of age. If they are at this age during mosquito season, consult your veterinarian. Always treat your pet during mosquito season in your area--late spring and summer in most areas of the United States. In warmer climates, it is advisable to treat year-round.

    Symptoms

    • Unfortunately, there are no early symptoms of heartworm. After approximately seven months from infection, your animal may start showing symptoms of heartworm, which include weight loss, coughing and lethargy.

      A blood test will detect heartworm by showing microfilariae in the blood, but this test is not consistently positive until the animal has been infected for seven months. At this point, the animal is severely infected and needs immediate treatment. Treatment for dogs is difficult and expensive. It is also very hard on the dog; it takes months for it to recover.

    Cats

    • There is no effective treatment yet for heartworm in cats. Cats are more resistant hosts to heartworm than dogs and are often able to rid themselves of infection by themselves. However, if the worms grow, a cat will react severely to the dead worms being removed from its body. This may result in a shock reaction that is life-threatening.