Battle Ground Veterinary Clinic, P.C.
Wellness Care
Heartworms: Prevention, Testing, and Treatment
What are heartworms? Heartworms are large parasite roundworms. The adult worms are several
inches in length and live in the heart of several area domestic pets and wildlife including dogs,
cats, ferrets, coyotes, and foxes. Heartworms are transmitted through bites from mosquitoes
that have been infected with the heartworm disease from the blood of another host animal. The
larva then matures and makes its way to the heart of its new host. Adult heartworms grow to a
large size and cause damage to the heart and lungs through inflammation, inappropriate clot
formation, and congestive heart failure. The outcome of the disease is very serious and
potentially fatal.
Are heartworms a serious threat? Yes! According to research in 2001, over 247,000 heartworm
positive dogs and cats were reported in the United States. As Indiana has a plentiful supply of
mosquitoes, the likeliness of a bite is very high. Heartworm positive pets have been found in our
area and we strongly advise year round protection for all dogs and cats.
How can heartworm infestation be prevented? A once a month heartworm preventative such as
Interceptor or Heartgard can be given to dogs and cats with 100% effectiveness. These
preventatives are sold according to weight and require a veterinarian prescription. Additionally,
many of the heartworm preventative products help protect against common intestinal parasites
including roundworms, hookworms, and whipworms. (see our Intestinal Parasite link for more
details) The medication comes as a chewable flavored treat which most pets eat eagerly. We will
happily provide you with a prescription once your pet has had an annual physical exam and a
negative heartworm test.
Can prevention be stopped in the winter? It is strongly recommended to continue heartworm
prevention every month regardless of season. While mosquitoes are not as prevalent in the
winter months, just one bite can infect your pet. A heartworm blood test is only able to detect
infection which initiated 6 months or more before the test date. The best way to avoid
infestation is to give prevention once monthly year round.
What should I do if doses have been missed? If it has been 6 or more months since your pet’s
first missed dose, a heartworm test is necessary before restarting prevention. Giving prevention
to a heartworm positive pet is potentially fatal. If it has been less than 6 months, please call our
office for special instructions.
How is my dog tested? Dogs are tested with a simple blood test which is sent to an outside lab.
Results from this test are generally returned the next business day. Heartworm checks are
recommended yearly and typically performed during the annual exam and vaccination visit. If
doses have been missed, it is important to test more frequently to ensure valid results.
Why is my cat not tested? A reliable and accurate test does not exist for feline heartworm testing.
In addition, there is no approved drug for the treatment of a heartworm positive cat. It is
possible, however, for cats to contract heartworms and the awareness of this ailment is
becoming ever more prevalent. Giving a once monthly dose of prevention is highly encouraged
for cats and dogs alike.
What are the signs of a heartworm positive pet? Symptoms are most commonly coughing and
rapid breathing. Weight loss and vomiting may also occur due to heartworm infestation. If these
problems occur, please call our office to make an appointment for an exam and heartworm test.
Many pets, however, will not show any outward symptoms at first. This is yet another reason
why blood screening test are so valuable.
What if my dog tests positive? There is a treatment available for dogs carrying the heartworm
disease; however there is some risk involved with treatment. Side effects can range from mild,
such as pain at the medication injection site, to very severe. When a dog is diagnosed with
heartworm infection, a radiographic examination and additional blood work are performed to
rule out any other medical problems. The treatment then involves a series of injections. The first
treatment requires a three day hospitalization so the activity is restricted and the dog is closely
monitored for adverse effects. The medication used kills the adult heartworms and the dog’s
body must slowly break down these large worms. If the patient is too active during this time,
there can be severe and potentially fatal reactions in the lungs. The second treatment is given
one month later and requires a day’s hospitalization. Three months following the second
treatment, a heartworm test is performed to be sure we have successfully removed all adult
worms. As you can see, the treatment is quite involved and affected dogs can be left with
permanent damage in the heart and lungs. Our goal is to protect your pets and prevent this
serious illness!