Dogs And Heartworm Disease

By Lambert Vet Supply | 1/1/2017 | Posted to Dog Health

Mosquitos and target practice. Us versus them. We swat them, slap them, spray them and curse their existence, but still they vex us! Yes, it does seem like we have a bull’s eye painted on us at times. Sadly, it is not just a human burden, but also one animals must endure. Besides being annoying, mosquitos pose serious health risks for all.

Mosquitos serve as the gateway, the incubator, the means of delivery for a whole list of nasty diseases and infections for humans and pets. For dog owners, mosquitos transport one of the most dreaded conditions possible for canines - heartworm disease.

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What is a heartworm exactly?

The cycle to produce heartworms involves several players and events, but the mosquito is the common denominator in the process. Adult female heartworms living in an infected dog, fox, coyote, or wolf produce microscopic baby worms called microfilaria, which circulate in the bloodstream.

As a mosquito bites an infected animal for a blood meal, it picks up these tiny worms. Now, living inside the mosquito, these baby worms mature into “infective stage” larvae in about 10 to 30 days. Cats can get heartworm disease, tooReady for another meal, the mosquito will pass on these infective larvae when it bites another dog or wild animal. Via the bite wound, the infective larvae will enter its new host after being deposited on the surface of the animal’s skin, taking about six months to develop into adult heartworms inside the dog.

When fully grown inside a dog or other wild animal, heartworms can live for five to seven years. A female worm is 6-14 inches long and 1/8 inch wide and causes most of the damage. The male is about half the size of the female. As natural hosts and due to long life expectancy, it is possible for dogs to harbor several thousand worms in their hearts and adjacent large blood vessels when infected. Once inside a dog, the adult worms will produce microfilaria that will also continue to mature until they are adults, repeating the cycle.

What is heartworm disease?

Simply put, heartworm disease clogs up a dog’s heart and the major blood vessels leading to the heart and lungs. This heartworm blockage reduces the blood supply to other major organs of the animal’s body, especially the lungs, liver and kidneys. Prolonged blood reduction to vital organs can cause them to malfunction.

Learn about the heartworm life cycle in dogs

The worms obstruct the arteries leading to the lungs, irritating the lining of vessels that connect from the heart to the lungs. Overtime, these “worm jams” make the heart work harder to pump blood through the lungs to receive oxygen, eventually enlarging the heart and leading to failure.

Most dogs are diagnosed with heartworm disease between two and eight years of age because of the time involved to produce adult heartworms. Because of this, the disease may be well advanced when found. It is rare in young dogs since the microfilariae have not had time to mature.

Why is heartworm testing important?

The American Heartworm Society (AHS) makes strong recommendations for ANNUAL TESTING of every dog as part of a complete heartworm prevention program. The reasoning stems from its own estimates, which show only half of dogs in areas prone to heartworms receive the proper preventive medicine. This number is reduced further because only about 75% of canines receive all the required monthly doses.

The AHS recommends the following guidelines for proper heartworm disease prevention:

  • ALL dogs should be TESTED ANNUALLY for heartworm infection. This will allow a veterinarian to catch heartworms earlier for effective management.
  • Dogs should be tested for heartworm if an owner is going to switch from one preventive to another. If a pet owner selects another heartworm preventive option, there are specific time periods in which the pet should be retested in order to ensure the dog is protected. It will be necessary to test more often.
  • Puppies can begin taking heartworm preventives without testing first. This can begin under the age of seven months since it takes about six-and-one-half months after being bitten by an infected mosquito before the dog will test positive. Testing should occur four to seven months after starting the heartworm medication to determine the presence of a heartworm infection.

As always, consult with your veterinarian about testing schedules and options.

Related Article: Dog Owners Declare War on Heartworm Disease >>

Testing Options

A blood test can detect/confirm heartworm disease.

An antigen test will look for specific antigens from adult female heartworms, and has proven very successful in confirming canine heartworm infection. These tests are performed on-site by a local veterinarian or at many veterinarian reference laboratories. These tests are better at detecting female heartworms at least seven or eight months old, but less likely to find worms younger than five months old.

Developed in the late 1970s and early 1980s, antibody tests have largely been replaced by the more effective antigen test. However, the antibody test is the most common test used in finding heartworm in cats.

Testing positive. What now? Treating heartworm disease

If a dog is diagnosed with heartworm disease, work closely with a veterinarian in tackling the problem. The vet will need to assess what stage the infection is in and look for underlying conditions, which may hinder the dog’s recovery, such as heart and lung damage and liver and kidney function. These problems will have to be dealt with first before drug treatment can begin.

A continuing shortage of a drug called melarsomine hydrochloride, marketed as Immiticide®, has forced vets to look for other primary solutions in treating heartworm in some cases. Two of these are ivermectin and Noromectin. A vet may prescribe one of these and will give it in a series of deep-muscle injections in a dog’s back over a 24-hour period OR two or more shots given a month apart.

A vet will monitor for side effects and a dog will be required to maintain strict bed rest or short-term hospitalization to watch for signs of shock or other adverse results. The dog may be quite sore and stiff at the injection site so the vet may prescribe pain medication.

During the four weeks it takes for the worms to die, the dog must be kept from running and playing since the dying/dead worms may migrate to the heart or lungs and cause a life-threatening blockage. Monthly heartworm preventive medicine will also be administered during this time to catch other worms in development. Abnormal symptoms during the treatment like diarrhea, coughing, vomiting and depression should be reported to a vet.

Generally, the success rate for dogs treated for heartworm is about 98 percent and most will not require additional intervention. A few will require another treatment if heartworm tests still indicate a presence six months after the initial injections. It can take months before a dog will have a negative heartworm antigen test.

Due to Immiticide’s shortage, some vets have also used a “slow method” of treatment using Heartgard and doxycycline (prescription required) with positive results. Always consult with a veterinarian about the best treatment route for your dog.

What are the symptoms of heartworm disease?

Initial symptoms for an infected dog may be mild and subtle and are often chocked up to aging. Most dogs do not show any early signs of the disease, which means by the time it is caught it is usually in an advanced state, making it riskier and more difficult to cure. Heartworm disease is divided into four stages.

Stage One: Most dogs will appear healthy and happy and blood tests may even be negative at this phase. Some owners may notice a slight cough, but nothing will seem irregular for the vet even during an examination. However, many pet owners and vets will not realize there might be indicators of more serious issues. For pets later diagnosed with heartworm disease, one veterinarian did mention seeing signs of premature aging in dogs with gray around the muzzle and forelegs as a possible sign, but this has not been clinically supported.

Stage Two: Symptoms may have progressed enough to be detected during testing at this point. Other indicators may be fatigue after exercise or a lingering dry cough. This cough results from three things: bronchitis that develops as pieces of dying worms become trapped in the lungs, fluid accumulation in the lungs as the heart fails and the enlarged, damaged heart pressing on the dog’s esophagus. Signs of heart disease will appear on an x-ray. Lab tests may show mild anemia and urine analysis may indicate some minor protein loss.

Stage Three: At this point, the disease will show up well on x-rays. Dogs will continue to cough, exhibit tiredness from exercise or avoid exercise completely. Dogs may also have trouble breathing. Weight loss and severe vascular damage on an x-ray will appear. Lab work may show acute anemia and marked urinary protein loss.

Stage Four: Untreated, this stage of heartworm disease is fatal. The impact of the disease will be very noticeable with breathing issues, coughing, and marked exhaustion after exercise or hesitancy to exercise. Dogs can appear lethargic for extended periods of time as well. At this point, heartworm disease will have made an impact on other organs like the lungs, kidney and liver. A dog’s stomach may look pear-shaped or pot-bellied as his liver enlarges and fluid accumulates in the abdomen.

If a dog experiences the Caval Syndrome, it will collapse in shock and dark, brown urine will be evident. Heartworms will be visible by ultrasound and blood work will be abnormal. This dog is dying and the surgical removal of adult heartworms via an incision through the jugular vein is the only way to save it. If a dog manages to survive this medical emergency, any further heartworm infection treatment must wait until the dog is stable enough to return to an earlier disease stage.

Every stage of treatment for heartworm disease carries some risks. The longer heartworm disease goes undetected, the more difficult it is to cure. The best defense, of course, is a good offensive attack through a regularly, applied regimen of heartworm preventive medicine.

How can heart heartworm disease be prevented?

While the manufacturers and the ingredients will vary from brand-to-brand, pet owners must take into consideration what works best for his or her canine companion. Make sure the products specifically states it is chemically engineered to kill parasitic worms like heartworms, round worms and hookworms. It is always good to consult with a veterinarian about the best plan of action, but take into account if a spot-on treatment might be best if your dog is not a fan of chewable tablets. Both spot-on and tablet choice provide protection against heartworm disease. All of these chemical components work with varying capacities to prevent heartworm formation.

Four primary chemical-based treatment options exist for heart disease protection:

  • Ivermectin-The primary ingredient in Heartgard® Plus and several other brand names
  • Selamection-The principal ingredient in Revolution®
  • Moxidectin-The primary ingredient in Advantange Multi®
  • Milbeymycin Oxime-This combination is used by Sentinel®, Sentinel® Spectrum and Trifexis®

Not sure what product would work best for you? Consult with your vet to get the best possible product for your canine.

View our heartworm preventive comparison chart »

Take Preventive Action

Most vets agree on three things about preventive action, follow the product’s directions and administer it monthly on a regular basis AND maintain heartworm medication year-round. Cases of heartworm have appeared in all 50 states so even dogs that live in the northern United States are still at risk. Heartworm treatments are usually priced in the $30 to $40 range for a 6 to 12 month supply. Most veterinarians will begin heartworm preventive treatment as young as six or seven months in puppies to ensure life-long control, but always work with your vet to find the best course of action for a pet.

While people can take direct action against mosquito attack, pets must depend on humans for assistance when it comes to heartworm. Keep that bull’s eye off your dog when a mosquito is looking for a target and help him live a longer, happier life in return.

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The information contained in The Well Pet Post articles is not intended to replace a one-on-one relationship with a veterinarian and is not intended as medical advice. If you have a health con­cern about your pets, please consult with an appropriately-licensed veterinarian. Never dis­re­gard pro­fes­sional veterinary advice or delay in seek­ing it for your pets because of some­thing you have read on this blog or in any linked materials.
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