Heartworm Disease

What is heartworm?

Heartworms live in the heart, lungs and the surrounding blood vessels of pets, causing severe lung disease, heart failure and damage to other organs in the body. These worms can grow to be feet long!  Heartworm disease can affect many species from dogs to cats and ferrets, but heartworms also live in wolves, coyotes, and foxes (which are carriers).

How do dogs get heartworm?

Dogs are the natural host for heartworms, which means that heartworms that live inside the dog mature into adults, mate and produce offspring. If untreated, their numbers can increase, and dogs can have several hundred worms in their bodies. Heartworm disease causes lasting damage to the heart, lungs and arteries, and can affect the dog’s health and quality of life long after the parasites are gone. For this reason, prevention is the best option.

How is heartworm transmitted?

The mosquito plays an essential role in the heartworm life cycle. Mosquitos are how heartworm is transmitted from animal to animal.  Adult female heartworms living in an infected dog (or other species) produce microscopic baby worms called microfilaria that circulate in the bloodstream. When a mosquito bites and takes a blood meal from an infected animal, it picks up these baby worms, which develop and mature into “infective stage” larvae over a period of 10 to 14 days. Then, when the infected mosquito bites another dog, the infective larvae are injected into the new host through the mosquito’s bite wound. Once inside a new host, it takes approximately 6 months for the larvae to mature into adult heartworms. Once mature, heartworms can live for 5 to 7 years in dogs.  Because of the longevity of these worms, each mosquito season can lead to an increasing number of worms in an infected pet.

What are the signs of heartworm in dogs?

In the early stages of the disease, many dogs show few symptoms or no symptoms at all. The longer the infection persists, the more likely symptoms will develop. Active dogs, dogs heavily infected with heartworms, or those with other health problems will often show clinical signs.

Signs of heartworm disease may include a mild persistent cough, reluctance to exercise, fatigue after moderate activity, decreased appetite, and weight loss. As heartworm disease progresses, pets may develop heart failure and the appearance of a swollen belly due to excess fluid in the abdomen (condition of heart disease). Dogs with large numbers of heartworms can develop sudden blockages of blood flow within the heart leading to a life-threatening form of cardiovascular collapse. This is called caval syndrome, and is marked by a sudden onset of labored breathing, pale gums, and dark bloody or coffee-colored urine. Without prompt surgical removal of the heartworm blockage, few dogs survive.

What is the risk of heartworm in New York?

Stray and neglected dogs and certain wildlife such as coyotes, wolves, and foxes can be carriers of heartworms, which those types of animals will not be on any type of prevention. Mosquitoes blown great distances by the wind and the relocation of infected pets to previously uninfected areas also contribute to the spread of heartworm disease.

Transporting and relocating dogs have become increasingly common practices for many valid reasons. Whether the situation is a pet accompanying their traveling owners or the necessary relocation of homeless animals for adoption, these exercises carry a risk of spreading infectious diseases.  This includes the transmission of heartworm disease.

The recent devastation with Hurricanes Harvey and Irma will increase the threat of heartworm disease through the relocation of dogs who lived in endemic heartworm areas into new communities, including New York State, where heartworm may not currently be entirely common.  The same incidence occurred following Hurricane Katrina.  Following that storm, nearly 250,000 pets were adopted and transported throughout the country forever changing the incidence of heartworm in many areas of the country.  The American Heartworm Society and fellow veterinarians in clinics and shelters throughout Texas and Florida are warning that nearly 80% of dogs over 6 months of age could be heartworm positive.  Heartworm disease is already highly prevalent in the southern half of the United States and as it is spread by mosquitos, its incidence is expected to unfortunately increase due to the significant amounts of rainfall that has occurred in these areas.

The loving and well deserving pets from these areas are in need of forever homes, but they can potentially be afflicted with this serious disease.  An adoring companion can be found amongst these pets displaced by the hurricanes but make sure to ask the adoption organization you are working with whether their animals have been tested for heartworm disease.  Also, based on the life-cycle of the heartworm itself, your pet may need to be re-tested at some point in the future to establish if your pet is indeed free of heartworm infection.

To also reduce the risk of heartworm for your pet at home, heartworm prevention is key.  This disease is 100% preventable if your pet is on monthly prevention.  There are many different safe and effective option for heartworm prevention for your specific pet.

Many factors must be considered, even if heartworms do not seem to be a problem in our area.  Our area may have a greater incidence of heartworm disease than you realize, these following examples should be taken into consideration when thinking of prevalence.

You may unknowingly travel with your pet to an area where heartworms are more common.  Many people from this area travel to Florida during the colder months, or others have relatives or travel on vacation to the south (South Carolina, Tennessee for example) are states that are all heavily infected with heartworm.

The fact is that heartworm disease has been diagnosed in all 50 states, and risk factors are impossible to predict. Multiple variables, from climate variations to the presence of wildlife carriers, cause rates of infections to vary dramatically from year to year.  And because infected mosquitoes can come inside, both outdoor and indoor pets are at risk.

At the Village Veterinary Clinic of Hamburg we have had a couple of heartworm positive dogs this past year.  These dogs had come to the area from the south, but the statements above are still true.  New pets come to the owners and they are unaware of their heartworm status.  They were not tested, or on any type of preventative.  There is no way of knowing how long they have been positive.  There is also no way to know if they were exposed to any mosquitos, then allowing that mosquito to travel and infect the next pet.

While it is true that the northeastern states do not have a great number of heartworm cases, we do get at least a few every year.  There have been a few dogs in the past few years that have never left the area and they were heartworm positive.

Here is an actual video from one of those heartworm positive dogs! We take a blood sample and look under the microscope for the worms, called microfilaria.  These worms live in the bloodstream and when they mature they go to live in the heart, lungs, and surrounding blood vessels!

How is my dog tested for heartworm?

Heartworm disease is a serious, progressive disease. The earlier it is detected, the better the chances the pet will recover. There are few, if any, early signs of disease when a dog is infected with heartworms, so detecting their presence with a heartworm test administered by a veterinarian is important.  Heartworm testing is very simple and everything is done at the hospital.  It just requires a few drops of blood from your dog.  We are able to receive results within 10 minutes.  If positive, further testing may be required by the veterinarian.  The tests we have at the hospital, test for antigens or exposure to the disease.

When should my dog be tested?

Puppies under 7 months of age can be started on heartworm prevention without a heartworm test (since it takes at least 6 months for a dog to test positive after it has been infected), but should be tested 6 months after your initial puppy visit.

For adult dogs (7 months and older), if your pet has never been on any preventative, we will do a heartworm test, confirm that is negative.  We will then need to repeat the test again in 6 months (if your pet got bit by a mosquito the day before your test, it will take 6 months to show up positive, need to confirm no disease).

We are advocates for year round prevention.  This disease is 100% preventable if on heartworm medications year round.  If you are on medications year round we test every 2 years.

If you choose to do prevention on a “seasonal” basis, we will test yearly.  Just remember, in this area seasonal typically was April-October.  We are now having warmer days in the middle of November, so our “seasonal” months are changing.  If this is occurring, please keep your dog on preventative for longer duration.

If you choose to test and not medicate, we will test yearly to ensure that your pet is still negative for heartworm.

If you are also getting your heartworm medications elsewhere (online, for example), we will test yearly.  We do this because we cannot ensure that the product you are getting is the actual product, with correct formulation, dosing, etc.  The companies that create these products will not guarantee their online sold products for this reason as well.  They will only guarantee products sold through veterinarians.

What happens if my dog gets heartworm?

No one wants to hear that their dog has heartworm, but the good news is that most infected dogs can be successfully treated.

The veterinarian will confirm the diagnosis. Once a dog tests positive on an antigen test, the diagnosis will be confirmed with an additional test (called a Knott’s test, which looks for the microfilaria, this test is sent out to an outside lab). The treatment regimen for heartworm is both expensive and complex.  According to the American Heartworm Society Guidelines. their are diagnostics necessary to begin.  Chest x-rays are necessary to look at the size, shape of the heart.  We look at the lung patterns.  We want to see if there is any inflammation or damage occuring.  We also run a full panel of regular bloodwork (CBC, chemistry panel, electrolytes) to determine if other body organs are functioning or if they are affected by the disease.  We then need an echocardiogram (done by an internal medicine specialist), they need to confirm the amount of heartworms present and classify the disease condition of your pet.  Once that is completed, we can administer the treatments.  To treat heartworm it is typically injections of an immidicide, which will kill off the adult heartworms. Dogs with no signs or mild signs of heartworm disease, such as cough or exercise intolerance, have a high success rate with treatment. More severe disease can also be successfully treated, but the possibility of complications is greater. The severity of heartworm disease does not always correlate with the severity of symptoms, and dogs with many worms may have few or no symptoms early in the course of the disease.

After treatments strict exercise is needed. Your dog’s normal physical activities must be restricted as soon as the diagnosis is confirmed, because physical exertion increases the rate at which the heartworms cause damage in the heart and lungs. The more severe the symptoms, the less activity your dog should have.  While the heartworms are dying off after the immidicide, rest is needed to help reduce the amount of inflammation that is being caused and the risk of reaction.

Test and prevent. Approximately 6 months after treatment is completed, a heartworm test is done to confirm that all heartworms have been eliminated. To avoid the possibility of your dog contracting heartworm disease again, you will want to administer heartworm prevention year-round for the rest of their life.

How do heartworm preventatives work?

All approved heartworm medications work by eliminating the immature (larval) stages of the heartworm parasite. This includes the infective heartworm larvae deposited by the mosquito as well as the following larval stage that develops inside the animal. Unfortunately, in as little as 51 days, immature heartworm larvae can molt into an adult stage, which cannot be effectively eliminated by preventives. Because heartworms must be eliminated before they reach this adult stage, it is extremely important that heartworm preventives be administered on a strict schedule (monthly for oral and topical products). Administering prevention late can allow immature larvae to molt into the adult stage.

What are the different types of heartworm preventatives available?

Heartgard: Prevents heartworm; kills hookworms and roundworms.

Revolution: Prevents heartworm; kills adult fleas; prevents flea eggs from hatching and prevents infestations; treats and controls ear mites; treats and controls sarcoptic mange; controls American dog tick infestations

Trifexis: Prevents heartworm; kills fleas and prevents infestations; treats and controls hookworms, roundworms and whipworms.

Check out these documents from the American Heartworm Society for additional information on heartworm disease:

For more information about heartworm visit: https://www.heartwormsociety.org

For more information about heartworm please visit: http://www.petsandparasites.org

For more information about heartworm please visit: http://www.capcvet.org

To see how prevalent heartworm is in your area visit: http://www.capcvet.org