Henderson Animal Care Hospital

PO Box 1987
Henderson, TX 75653



Heartworm Infection

in dogs


Heartworms are a very prominent parasite in the East Texas area.  The good news is, it can be PREVENTED!!!  Heartworms are spread through mosquitoes.  A mosquito carries heartworm larvae, called microfilaria.  When a mosquito bites a dog, it injects the microfilaria under the skin of the dog.  The microfilaria then travels through the blood stream to the right side of the heart.  There, it grows into an adult heartworm and starts to breed, making more microfilaria which in turn grow into adult worms in the heart.  A mosquito then bites the infected dog and picks up microfilaria from the blood stream, and the cycle starts all over again.  This cycle from microfilaria to adult breeding heartworms takes about 6 months.


Why this is a problem:  The heart's job is to pump blood to the lungs and the body.  The right side of the heart will pump blood to the lungs.  If you have 20-30 worms (20 cm in length each), you can imagine how much trouble the heart has pumping blood through to the lungs.  When this happens, blood begins to back up into the abdomen, and the adult heartworms begin to work their way to the lungs.  When blood starts to back up into the abdomen, it is called ascites, and the heart is starting to fail.


Clinical Signs to Look for: If your dog is not on heartworm prevention, he needs to be tested immediately!!  Some things you may notice in a positive dog: coughing, exercise intolerance, bloated abdomen, anorexia, pale mucous membranes, lethargy, and trouble breathing. 


Screening: We can perform a small blood test on your dog to determine if he has heartworms.  Even if your pet is on heartworm prevention, they must be tested once a year.  If your dog has not been on prevention, and he has a negative test today, he will also need another test in 6 months (see the life cycle above).


Prevention: Heartworms are easily prevented.  Puppies are able to start heartworm prevention as early as 6 weeks of age, and no later than 8 weeks of age.  If your puppy is over 6 months old, he will need a heartworm test before a preventative can be prescribed.  We have several monthly heartworm preventatives available, and your pet must have a heartworm test once a year to receive a prescription.


Treatment: Keep in mind, prevention is less expensive, and much easier on your pet.  If your pet is not on prevention, he needs to be tested NOW!!!  Treatment to kill adult heartworms consists of 3 injections into the lumbar muscles.  The first injection is administered, then 30 days later, 2 injections are given 24 hours apart.  During this time, your pet may experience side effects, and strict cage confinement is necessary.  Depending on the severity of heartworms in your pet, your veterinarian may prescribe oral medications for a few weeks before treatment is initiated.


For more information, please visit the American Heartworm Society page.