What is heartworm?

Heartworm disease is a serious and potentially fatal condition caused by
parasitic worms living in the arteries of the lungs and occasionally in the
right side of the heart of dogs, cats and other species of mammals. Heartworms are
classified as nematodes (roundworms) and are filarids, one of many species of roundworms.  Dogs and cats of any age or breed are susceptible to infection.

How does a dog get infected with heartworm?

The disease is spread by mosquitoes that become infected with microfilariae while taking a blood meal from an infected dog. Within the mosquito, the microfilariae mature into the infective larval stage.  When a mosquito carrying infective heartworm larvae bites a dog and transmits the infection, the larvae grow, develop and migrate in the body over a period of several months to become sexually mature male and female worms.  These reside in the heart, lungs and associated blood vessels. As mature adults, the worms mate and the females release their offspring (microfilariae), pronounced: (micro-fil-ar-ee-a), into the blood stream.  Offspring can be detected in the blood (pre-patent period) about six to seven months after the infective larvae from the mosquito enter the dog. The male heartworms (four to six inches in length) and the females (10-12 inches) become fully grown about one year after infection, and their life span in dogs appears to average up to five to seven years.

I thought heartworm was only in the South? Can my dog get heartworm anywhere else?

This is a HUGE misconception. Although heartworm is believed to be more prevalent in the South, it has mitigated all over the US.  Canine heartworm infection is widely distributed throughout the United States.  Heartworm infection has been found in dogs native to all 50 states. All dogs,  regardless of their age, sex, or habitat, are susceptible to heartworm infection.  Regions where heartworm disease is common have diagnosed infections in dogs as young as one year of age, with most areas diagnosing infections primarily between the ages of three and eight years. Although there are differences in frequency of infection for various groups of dogs, all dogs in all regions should be considered at risk, placed on prevention programs and frequently examined by a veterinarian.

How do I know if my dog is affected?

A heartworm infected dog with mild disease may appear to be perfectly normal
upon physical examination. Severely affected dogs, however, may show signs of
right-sided heart failure. Labored breathing or crackles may be heard in the lungs due to vascular clots and elevated pressure. A history of coughing and inability to exercise are among the earliest detectable abnormalities. Tachycardia (rapid heartbeat), ascites (fluid in the abdomen) and hepatomegaly (enlarged liver) indicate right-sided
congestive heart failure. Hemoptysis (blood in the sputum) occasionally occurs and indicates severe clots and complications within the lungs. Anorexia (loss of appetite), cachexia (severe weight loss), syncope (fainting) jaundice or yellow bile pigmentation present in the skin and mucus membranes may appear in severely affected dogs. Clinical signs and disease experienced in such infections depend largely on the location of the worms. The primary response to the presence of heartworms in dogs, however,
occurs in the heart and lungs.  A yearly heartworm blood test is recommended for dogs to see if they have been infected.  Once a dog has a positive test the next step is typically x-rays, ultrasounds or labratory bloodwork to see the extent of the infection.

How is heartworm treated once a dog is infected?

There is currently one drug approved by the FDA for use in dogs for the elimination of adult heartworms. This drug is an organic arsenical compound. Dogs receiving this drug therapy will typically have had a thorough pretreatment evaluation of its condition and will then be hospitalized during the administration of the drug.  Melarsomine dihydrochloride (Immiticide®, Merial) has demonstrated a higher level of effectiveness and safety than any other adult heartworm treatment previously available. It is  administered by deep intramuscular injection (very painful for the dog) into the lumbar muscles. These injections are given after completing 30 days of doxicycline and 60 days of an ivermectin treatment (we currently use heartgard).  Depending on the severity of the heartworm, there are 2-3 injections.  The first injection is given, 30 days later another injection is given and then the third injection would be given 24 hours after the second injection if necessary.   During this treatment, the dog must be on complete crate rest and have very little activity except to go out on a leash to go potty.  This is to reduce the risk of complications.  The primary post-adulticide complication is the development of severe pulmonary thromboembolism. Pulmonary thromboembolism results from the obstruction of blood flow through pulmonary arteries due to the presence of dead heartworms and lesions in the arteries and capillaries of the lungs. If heartworm adulticide treatment is effective, some degree of pulmonary thromboembolism will occur.  When dead worms are numerous and arterial injury is severe, widespread obstruction of arteries can occur. Clinical signs most commonly observed include fever, cough, hemoptysis (blood in the sputum) and potentially sudden death. It is extremely important to not allow exercise in any dog being treated for heartworms. Often dogs with severe infections will also require the administration of anti-inflammatory doses of corticosteroids.

How can I prevent this in my dog?

While treatment of canine heartworm disease is usually successful, prevention
of the disease is much safer, more economical and PAINLESS for the animal and owner. There are a variety of options for preventing heartworm infection, including daily and monthly tablets and chewables and monthly topicals.  These products  are extremely effective and when administered properly on a timely schedule, heartworm infection can be prevented.  The American Heartworm Society is now recommending year-round prevention, even in seasonal areas. One reason for this is compliance – to make sure the medicine has been given properly by the pet owner. In addition, most monthly heartworm preventives have activity against intestinal parasites. Many of these same intestinal parasites that infect dogs can also infect people, with estimated infections occurring in three to six million people every year. So this added benefit of monthly deworming makes great sense.  Before starting a preventive program, all dogs should be tested and examined by a veterinarian.

Pictures of heartworms and actual hearts infected with heartworm....

Clicking on the link here will show you the cold truth about heartworm.  The photos are graphic, so please use discretion when viewing.