Family - Pets
By: - at May 31, 2013

How To Keep Your Dog free of Heartworm Disease

Dogs may be infected with different types of worms including hookworms, tapeworms, round worms, and heartworms. These worms affect dogs differently depending on the type of parasite and the worm burden. Dogs infected with heartworms tend not to show indications of infection in the first six months before the worms mature to adults. These worms can affect the health of your dog and in severe cases, they can lead to death. It is important to learn how to detect if your dog may be infected with heartworms so that treatment can be sought in advance.

What are dog heartworms?
Heartworms also known as Dirofilaria immitis are parasitic roundworms that can infect dogs and other animals like cats, foxes, wolves, and sea lions. The worms can also infect humans but on very rare occasions. Heartworm disease is a type of filarial disease transmitted by mosquitoes from one host to another. The dog acts as the definitive host meaning that without man's best friend, these worms would of probably not made it to adulthood.

Heartworms mature and reproduce in their definite host like the dog. A mosquito is an intermediate host where the worms live for a short period of time before they are passed to a dog. Inside a mosquito’s body, this is where the larvae of the worms become infective meaning that they develop the ability to cause heartworm disease. Without the mosquito, heartworm larvae cannot become infective.

Infected Dog Heart - The White Stringy Things Are Worms:
Infected Dog Heart - The White Stringy Things Are Worms
By Alan R Walker via Wikimedia Commons

Although the parasites are referred to as heartworms, they tend to cause more damage on the lungs because in the better part of their life they largely inhabit the lung arteries as well as the pulmonary artery blood vessels. Nonetheless, adult worms may move and reside on the right side of the heart of a dog where they live in the great veins causing damage to the heart.

How do heartworms infect dogs?
Heartworms are spread through mosquito bites. When the heartworms develop to adults, the females release offsprings known as microfilariae, which move to the bloodstream of a dog. If a mosquito bites a dog infected with microfilaria, the mosquito gets infected with these offsprings. The microfilariae live in a mosquito for about 10 to 14 where they develop to infective larvae.

How do heartworms infect dogs
By Anka Friedrich via Wikimedia Commons

One thing with these heartworms is that the microfilariae cannot become infective if they do not pass through a mosquito. If the mosquito bites a healthy dog, it infects it with the larvae through the bite wound. When heartworm larvae have entered the bloodstream of a dog, it takes about 6 to 7 months for them to develop to adult worms.

Removed Heatworms:
Removed Heatworms

After the worms reach maturity, they begin mating and reproducing in a dog with the females releasing their offsprings into the bloodstream. Once the offsprings are released to the dog’s bloodstream, the lifecycle is complete and larvae can start infection in other dogs when picked by a mosquito. Heartworm disease is only spread through a mosquito bite and it is not a contagious disease.

How can you detect that your dog is suffering from heartworm disease
Heartworms cause various complications when they infect a dog and the symptoms will largely depend on the worm burden (the number of worms in a dog), the dog size, the level of activity or activeness of the dog and the parts of the body where there is heavy infestation. These worms cause organ failure including the heart, lungs, liver, and kidneys as well as infection of the surrounding tissue like the blood vessels. In their early infection, dogs may not show signs and they can lead a pretty normal life. However, when the infection is high or the dog is very active, the signs begin to show up.

How can you detect that your dog is suffering from heartworm disease

As the infection progresses, physiological changes are witnessed in the dog’s body. The advancement of the infection can be categorized into different stages which include;

  • Stage I - This is the initial period of infection and in most cases, there may be little signs or no noticeable signs at all. In this stage, the infection has already begun and it is only a matter of time before the dog is overwhelmed by the worm burden. One symptom noticed in a dog at this stage is an occasional mild cough. If your dog has started coughing, you need to contact a veterinarian to examine it.
  • Stage II - In this stage, your dog shows mild to moderate symptoms. The number of worms may have increased causing more harm that begins to show signs. The coughing is still occasional and the dog appears tired after a moderate physical activity.
  • Stage III - This is where the signs show up clearly. As the worm infection advances, the dog suffers more. The occasional coughing becomes frequent. Your dog experiences a weight loss. It also looks unwell and may spend much of its time resting in a corner of your home. After a mild activity, the dog seems very fatigued. Moreover, your dog also shows complications in breathing and the heart may begin failing. A chest x-ray may be required to examine the damages in heart and lungs due to increased worm burden.
  • Stage IV - This is the most serious stage of heartworm disease and is referred to as the vena cava or caval syndrome. Heavy worm burden leads to blockage of blood vessels causing impaired flow of blood back to the heart. Dogs that have reached this infection stage require surgical procedure to remove the worms. However, not many dogs will survive the caval syndrome and they will eventually die even after a surgery. Nonetheless, some dog heartworm infections may not develop to caval syndrome.

In severe infections, a dog may show abnormal sounds of the lungs and liver enlargement. Your dog may also show signs of fainting due to poor circulation of blood to brain arising from blockage of blood vessels by the worms something that leads to temporary loss of consciousness.

sick dog

In addition, a dog may have abnormal heart sounds and fluid that accumulates in the abdominal cavity. Such symptoms can easily lead to death of your dog if not checked immediately.

Diagnosis of Heartworms in a Dog
Different tests may be performed to determine the presence of heartworms and microfilariae larvae in the body of a dog. These tests include antigen test, microfilarial concentration test and chest X-ray. The most accurate test is the antigen test, which involves identifying an antigen that is produced by adult female heartworms. However, in this test, there may be false results especially during early infection before the worms develop to adults.

Chest X-rays May Show Signs of Heartworms in Dogs:
Chest Xrays May Show Signs of Heartworms in Dogs

A false antigen test may also occur if there are few adult heartworms in body and when the worms are only males. When all's said and done, false tests are a rare occurrence. Dogs that have few worms remain asymptomatic and they may not show symptoms until the number of worms has increased substantially to begin causing more harm.

A veterinarian may also perform a microfilarial concentration test. In this test, a blood sample is taken and examined under a microscope to find out if there are microfilariae in the blood specimen. Again, a negative test result may occur but this does not rule out presence of the infection. This is because; about 10 to 25 percent of dogs do not have microfilariae in the peripheral blood. This means that a dog may be infected with the worms but they have not yet migrated to the peripheral blood.

microfilarial concentration test heartworm test

In severely ill dogs, chest x ray is the best test to perform because it shows the extent of damage that the worms have caused. With heavy infection or high worm burden in pulmonary artery, the imaging may show enlargement of the heart ventricle. Other tests may also be done such as an electrocardiogram-ECG, which may show heart arrhythmias and enlargement of the right ventricle.

Because low worm burden may result to asymptomatic condition where no signs are noticed in a dog, this can prevent the early detection of the infection. This gives the worms a chance to multiply inside the dog’s body thus causing harm. By the time the worms are detected, they have already caused serious health complications to your dog. For an effective treatment and to save the life of your dog, an early diagnosis of heartworm disease is needed.

What are the treatment options available for dog heartworm infection?
Treatment of heartworm disease in dogs is aimed at eliminating microfilariae and the adult worms. The treatment of the infection depends on severity of the symptoms and the location where there is heavy infection. Complications of drug toxicity as well as dislodging of dead worms to the lungs should be examined when providing treatment.

There are two drugs that have been approved by the FDA in treating heartworm disease in dogs and they are namely; thiacetarsamide and melarsomine. Of these two drugs, melarsomine, which is sold under the brand name immiticide, is safer than thiacetarsamide which is marketed under the name Caparsolate.

immiticide melarsomine

It is important that you discuss with the veterinarian on the most suitable drug to be applied in treating your dog of heartworm infection. The thiacetarsamide drug is injected directly into the vein (intravenously). The drug may be administered two times a day for two days. The use of thiacetarsamide or Caparsolate has side effects like loss of appetite, vomiting, diarrhea, jaundice, and failure of the kidney. This drug can cause toxic reactions and at times it can lead to death of the dog.

Another disadvantage of using thiacetarsamide drug is that it may not destroy all the worms because the immature ones that have not developed to adults tend to resist this medication. Before your dog is administered with Caparsolate, it should be evaluated to ensure that it does not have high health risks like kidney, heart, and liver complication. This is because; dogs with these complications are not suitable for the drug.

dog being treated for heartworms

On the other hand, Immiticide or melarsomine is more effective in treating heartworm disease and it is capable of destroying up to 90 percent of the worms. Another advantage with this drug is that it has fewer side effects and it may be a good alternative for dogs that have problems of the liver, heart and kidneys. However, it requires close supervision by a veterinarian when administering these drugs.

Immiticide is administered through intramuscular injections. It is injected once in a day for two days though the period of administering the drug may vary depending on severity of the worm infection.

heartworm medications

A surgical procedure is applied in treating dogs that are seriously ill. If your dog has the vena cava syndrome (a serious and very severe infection of the heartworm disease), the most appropriate treatment is a surgical procedure. A surgery reduces the risks of kidney and liver failure in seriously ill dogs. It also minimizes the risks of thromboembolism or dislodging of dead worms into the veins causing blockage in blood flow.

A follow-up treatment is needed to ensure that all the worms and microfilariae have been eliminated. When adult worms are killed with use of drugs, a veterinarian may advise you to wait for a few weeks before your dog is treated of larvae or microfilaria. Treatment of microfilariae may be done with drugs like ivermectin. This is the most effective drug in destroying microfilariae and it has fewer side effects.

To help fight heartworm disease in dogs, you need to ensure that you keep your dog away from mosquitoes. However, this may not be easy and what you need to do is ensure that your dog remains indoors in the evenings and afternoons to avoid mosquito bites. Mosquitoes tend to actively feed during the evenings and afternoons.

dog kept indoors

Another way you can control heartworm infections is by spraying your yard with insecticides to kill mosquitoes. The mosquitoes breed in areas with stagnant water and this means that if there are any swampy areas within your premises, the waters should be removed. In areas that are prone to heartworm infections, dog heartworm prevention pills may be used as prevention measures. Last but not least, your dog may need to be tested after sometime to determine if it has been infected with these dangerous worms.

By Chemically Treating Your Yard You Decrease the Likelihood of Heartworms:
By Chemically Treating Your Yard You Decrease the Likelihood of Heartworms

In a nutshell, the severity of heartworm disease is determined by the number of worms in a dog. A dog may have one to 250 worms and the more the number, the severe the symptoms. The activity of the dog also determines how severe the heartworm disease symptoms are. In addition, the period of infection and the way in which the dog’s body responds to the infection also determines the severity of symptoms. The first signs you should look for in a dog are occasional coughing, change from active state to a sedentary life, and lethargy after a mild activity.





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