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Heartworm: why your dog needs prevention.

Updated: Oct 31, 2020

Heartworm is on the rise in the Northeast. It's a dangerous condition. It's also preventable.

First off, let's talk about what heartworm is and how it is spread. 

Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and 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.

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 bloodstream.  Offspring can be detected in the blood 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 and slowly kill the animal it is hosting off of.  Imagine how uncomfortable it would be to have worms like that all around your heart and lungs.

Heartworm disease is a serious and potentially fatal condition caused by parasitic worms living in the arteries of the lungs and the right side of the heart of dogs, cats and other species of mammals.

It is a HUGE misconception that heartworm is only in the South. Although heartworm is 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. If you have mosquitos, you have a risk of heartworm.  Regions where heartworm disease is common have diagnosed infections in dogs as young as under 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. 

This year alone we have been involved with a dozen heartworm treatments for dogs in rescue that tested positive and lived here in Pennsylvania their whole lives. 

Unfortunately, you will not know looking at your dog if it becomes infected.  A heartworm infected dog with mild disease may appear to be perfectly normal upon physical examination. Severely affected dogs, however, may show signs of heart failure. Labored breathing or crackles may be heard in the lungs due to vascular clots and elevated blood pressure. 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 mucous membranes may appear in severely affected dogs. Clinical signs 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 heartworm positive dog puts animals within a 5-mile radius at higher risk of being infected. 

So how can you protect your pet?  A heartworm blood test is recommended for dogs to see if they have been infected in which your veterinarian can do.  If the test is negative, the dog can be placed on preventative measures.  NEVER put your dog on preventative without a negative blood test. This could be deadly for the dog. If you have a lapse of 3 months of the preventative, retest your dog before giving any preventative.  If the dog has a positive test, the next step is typically x-rays, ultrasounds and more bloodwork to see the extent of the disease.  The current recommendation is 60 days of doxycycline with heartgard administered monthly.  Then you have three sets of injections day 60, day 90 and day 91.  A medication by the name of Immiticide Merial.  It is a series of three deep muscular injections in the lumbar area.  This is very painful but necessary for the dog to rid the worms.  During heartworm treatment the animal must be kept on STRICT cage rest and have 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. The cost of this treatment is $1000 to $2000 dollars.

This all can be prevented by a monthly tablet.  A tablet year-round to keep your pet from having to go through this.   We recommend testing for heartworm yearly but at the very least every other year.  Please protect your pet.  We are seeing more and more cases every single year and the fact it is so easily preventable seeing this many cases is heartbreaking. No animal deserves to go through this.   

For more information, please visit the American Heartworm Society 

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