Heartworm Awareness

April is National Heartworm Awareness Month

Heartworm disease is a serious and potentially fatal disease that is widespread in pets. Heartworms live in the heart, lungs and blood vessels of affected pets. This causes severe lung disease, heart failure and damage to other organs in the body. Heartworms also live in other mammal species such as wolves, coyotes, foxes, sea lions and even humans in some rare cases.

Dogs are a natural host for heartworms, which means the worms that live inside your pet mature into adults, mate and produce offspring. Dogs have been known to harbor several hundred heartworms in their body.  Long lasting damage to the heart, lungs and arteries can affect the quality of life long after the parasites are gone.

Cats are an atypical host for heartworm. If they do become infected, most of them do not survive into the adult stage. They generally only have 1-3 worms, which means that damage can occur.  Immature heartworms can cause damage in the form of a condition called heartworm associated respiratory disease (HARD). The medication used to treat dogs for heartworm disease can’t be used in cats.

How is heartworm transmitted from one pet to another?

       This is where the mosquito comes into play. The adult female heartworms that are living in coyotes, foxes, wolves, or dogs produce microscopic baby worms called microfilaria. These baby worms circulate in the blood stream. When the mosquito takes a blood meal from the infected animal, it picks up the baby worms which mature into “infective stage” larvae over the period of 10-14 days. The mosquito then bites a dog, cat or wild animal, in which the infective larvae are deposited on to the surface of the animal’s skin.  These larvae enter the new host within the wound left behind by the mosquito. It then takes 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5-7 years in dogs and 2-3 years in cats

Signs and symptoms

        Early stages of the disease may not be noticeable in your pet. The longer they are infected, the higher the chance is for symptoms to occur.

        Signs for dogs may include: Persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As heartworm disease progresses, heart disease may develop. The longer the disease is present and the more worms your pet has can cause blockages of blood flow within the heart that can lead to cardiovascular collapse which is life threatening. Unless your pet has emergency surgery to remove the worms from the heart, few dogs survive.

        Signs of heartworm in cats can either be subtle or very dramatic. Symptoms may include: Coughing, asthma like attacks, periodic vomiting, loss of appetite or weight loss. Unfortunately, in some cases, the first sign of symptoms is sudden collapse or sudden death.

Is your pet at risk for heartworm disease?

       Heartworm disease is spreading to new regions of the country each year. Even if you live in a place that doesn’t have a high incidence, you may travel with your pet not realizing that where you are going does have a higher incidence of heartworm. Also, stray, neglected and animals traveling to your area may be carrying it. For example, when hurricane Katrina hit, 250,000 pets, many of which were infected with heartworms were adopted out and shipped to all different parts of the country.

How and when should you test your pet?

        We use an in house blood test that can detect the heartworm antigen. We recommend testing your pet at 6 months of age and then yearly after that. It takes at least 6 months to show positive on the test. We recommend yearly after that.

If your pet has not been on heartworm prevention, the recommendation would be to test prior to prevention. You may be wondering why we recommend yearly testing if your pet is on prevention? We need to make sure the prevention they are on is working. Preventatives are highly affective, but giving one dose late or skipping could be the difference if your pet becomes heartworm positive. The National Heartworm Association is recommending year round prevention to be given.

        Heartworm disease is harder to detect in cats than dogs, because they don’t always have adult heartworms. We can antigen test for it, but the veterinarian may also take an x-ray or use an ultrasound to look for heartworms. Prevention is the best way to go for cats, especially since there is no approved treatment for them.

My pet tested positive, now what do I do?

       Not all dogs have microfilaria circulating in their bloodstream or have been on heartworm prevention drugs that kill microfilaria. We will perform an occult heartworm blood (ELISA) test to detect antigens (proteins) given off by adult female heartworms. Any dog that tests positive for heartworm disease will have additional testing done. We will perform chest x-rays to evaluate the size of your pets heart and see if there are any changes to their lungs. If heart failure is suspected, the Doctor may recommend an echocardiogram to make sure there is no other reason for heart failure to be occurring. Some laboratory testing will be done as well to check other internal organs as well. If other disease processes are found, those would be treated first since heartworm treatment can adversely affect the kidneys and liver.

The treatment used in dogs is an adulticide such as Immiticide. There are 2 different dosing schedules available:

1  1.      2 intramuscular injections are given 24 hours apart. This way kills 90-95% of adult heartworms usually in 2-3 weeks.

   2.    Dogs with right sided heart failure or changes in their lungs on x-rays are administered the Immiticide in split doses. This method kills fewer heartworms with each injection which limits the risk of worsening lung problems or acute death. With this treatment, 1 intramuscular injection is given, the pet is rested for 4-6 weeks, then 2 injections given 24 hours apart.  

This form of treatment is not recommended in cats because killing of the adult heartworms can be fatal if too many die at once. Cat’s lungs can’t handle more than 1-2 heartworms dying at once.

Products that have ivermectin such as heartgard can be used to slowly kill some of the adult heartworms if the product is given for at least 18 months. We do not recommend this method because if your dog is too active, you risk pulmonary embolism and sudden breathing problems. We only use this method if there are other health concerns going on at the same time.

Baby microfilaria can be treated after the adult heartworms have been treated. This is an oral form of ivermectin that we give, while your pet is hospitalized for the day so we can monitor. This kills a large number of microfilaria within 2-8 hours after the medication is given.

All pets are kept quiet for 6 weeks following treatment to prevent any pulmonary embolisms or acute death. 4-6 months out, we will run some additional testing to make sure the heartworm disease has cleared. If your pet remains positive, the treatment would be repeated.

Prognosis

Most dogs do well with treatment and are able to be started on prevention after treatment is complete. We have several types of preventions available depending what works best with your lifestyle. If your pet has kidney, liver, or lung changes problems during the treatment, prognosis is guarded if the problems persist after treatment. Some dogs are able to return to normal activity, but may not have the same energy level they had before. Dogs with right sided heart failure may have a poor prognosis because of the treatment and may need treatment for the rest of their lives. 

Preventions

We have different preventions available. We offer monthly chewables, monthly topicals or a 6 month injection available.