Longenbaugh Veterinary Hospital P.C.

15703 Longenbaugh, Ste. F
Houston, TX 77095



Longenbaugh Veterinary Hospital / Animal Hospital of Cypress Happy Dog 77095. Come see Henry!

Understanding Heartworm Prevention!


How do heartworm preventatives work?
Why does my pet need a yearly heartworm test?
Why don't all veterinarians have the same policy?

Hopefully the information in this article will answer these questions.  Heartworm disease is a serious disease that results in severe lung disease, heart failure, other organ damage, and death in pets, mainly dogs, cats, and ferrets. It is caused by a parasitic worm called Dirofilaria immitis. The worms are spread through the bite of a mosquito.  The dog is the definitive host, meaning that the worms mature into adults, mate, and produce offspring while living inside a dog. 

The heartworm has several stages.  Heartworm preventatives work to kill the initial stages.  Your preventative works by killing the larvae that have infected your dog during the PREVIOUS 30 days.  Many people think it protects for the next 30 days, but it doesn’t.  If you are not consistent with your preventative, it is possible that some larvae may reach the stage which is not affected by the preventative. These can grow into adult worms and cause heartworm disease.  The key to preventing heartworm disease is giving a preventative every 30 days. 

A heartworm test is a test to see if your pet has adult heartworms.  If a heartworm-positive dog is not tested before starting a preventative, the dog will remain infected with adult heartworms until it gets sick enough to show symptoms.  Also, giving a heartworm preventative to a dog that has an adult heartworm infection may be harmful or deadly.  If microfilariae are in the dog's bloodstream, the preventative may cause the microfilariae to suddenly die, triggering a shock-like reaction and possibly death in some dogs. The test does not detect early stage larvae. A dog may appear healthy on the outside, but on the inside, heartworms may be living and thriving. A pet with no history of prevention should be tested initially. If no adult heartworms, the test will be negative and the pet can start Heartgard. Heartgard is the safest for these pets. The pet should be retested in 6 months to check for adult heartworms.  Remember that the initial dose of preventative only works to kill larvae for the previous 30 days.  Unfortunately there is a possibility that a pet will have larvae too young to be picked up on the test and too old to be affected by the preventative.  Carlos the pit-bull stray that we were fortunate to have come into our lives for 5 years until his death in October tested negative when we found him and 6 months later he tested positive.  We gave him heartworm preventative regularly, but we knew there was the possibility he could still be positive and he was.  He was treated and survived. The treatment is hard on pets, but the disease is even harder on pets and very expensive to treat.  A heartworm test is necessary.

Unfortunately many pet owners are not thoroughly educated on heartworm disease or how preventatives work.  Our emphasis at Longenbaugh is client education and pet health.  We adhere to our heartworm policy because it is based on the latest veterinary medical and American Heartworm Society recommendations.