Dog Heartworm Symptoms

 Dog Heartworm Symptoms-Diagnosis Treatment and Prevention

dog heartworm disease lethargicHeartworms are parasitic roundworms that are spread from one host to another through mosquito bites, and only months later will your dog start having dog heartworm symptoms. These worms are a type of filarial and they appear like small threads. Heartworm is also known as Dirofilaria immitis. Dogs are definitive hosts for heartworms and this means that the worms will inhabit, mature, and reproduce inside the body of these animals causing dog heartworm symptoms. Whereas the dog is the definitive host, mosquitoes are referred to as the intermediate hosts because the worms live inside mosquitoes for a relative short transitioning period. During this period they live in mosquitoes, worms larvae grow to be infective or develop the ability to cause heartworm disease.

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dog heartworm symptoms


Although heartworms infect dogs, they may also infect cats, foxes, wild felids, wolves, coyotes and in rare cases humans. The parasites are given the name heartworms, though actually they inhabit the lung arteries along the pulmonary arterial vessels for the better part of their lifespan in dogs, and this is why much of the primary effects on the health of a dog manifest as damage of the lung blood vessels and surrounding tissues. In other times adult heartworms migrate to reside in the right side of a dog’s heart where they could extend to inhibit blood flow in the great veins in cases of heavy infections, and this eventually causes damage to these parts if the dog heartworm symptoms are not treated.

Clinical signs and symptoms of heartworm disease in dogs

Dog Heartworm Symptoms TiredHeartworms can cause different health problems in a dog and they include infections and failure of organ like lungs, liver, heart and kidneys and corresponding tissues. The liver and heart are the most susceptible to the damage caused by these worms, and this is particularly because the adult worms live in the arteries of these organs which results to damage of the blood vessels and tissues. Usually in the early stages of the infestation, there may not be noticeable heartworm symptoms. However as the infection progresses it results to chronic infestation that is accompanied by physiological changes in the body of a dog. When the worms have infected the dogs body the infestation can have an acute onset. In normal cases, dogs with a low number of worms (worm burden) infestation especially those that are not exercised vigorously may not show signs of the disease.

Although on the onset of infestation, no abnormal clinical signs are noticed, when the disease develops to mild levels, dog heartworm coughing signs are witnessed. As the infestation progresses to moderate levels, the coughing may be accompanied by intolerance to exercise or strenuous body activity, and abnormal lung sounds.

In its severe form, heartworm disease shows signs of coughing, intolerance to strenuous activity and difficulties in breathing, a condition known as dyspnea. Severe dog heartworm symptoms are also characterized by abnormal lung sounds and enlargement of the liver (hepatomegaly). Likewise, a dog with severe infection may also show signs of fainting or temporary loss of consciousness (syncope). This condition is caused by poor supply of blood to brain. A dog may also develop abnormal sounds of the heart as well as accretion of fluid in the abdominal cavity, a condition known as ascites. If not treated, severe infection may result to death.

Stages of heartworm infection

There are ideally four stages or classes of heartworm infection and the higher the class the more serious the condition is and the more the heartworm symptoms are pronounced. The severity of heartworm disease has a direct correlation with the number of worms inside a dog or the worm burden. The worm burden number may range from 1 to 250 worms in a dog. The severity of the disease also depended on how the body of the dog responds to these worms and the period the infestation has taken. In addition, the activity of the dog helps determine the severity of the infestation.The severity of the condition may also be determined by aspects such as when the symptoms are first seen because they may not easily be noticeable or detected in dogs with low worm burden. Below are the stages of heartworm infection;

Stage 1- In this stage, there may be no dog heartworm symptoms at all, though the infestation has already started. Similarly, there may be mild symptoms such as occasional cough.

Stage 2- In this level of infection, a dog shows mild to moderate symptoms. An occasional cough may be witnessed which is accompanied by feeling of weariness even after a moderate activity.

Stage 3- As the infestation advances, the body becomes weak and the dog may lose weight and show general loss of body wellbeing. The occasional cough now becomes persistent. In addition, in this stage, there is tiredness after having mild activity. A dog also experiences troubles in breathing and heart failure may be witnessed. During this level of infestation, changes in heart and lungs can be detected by use of chest X-rays.

Stage 4- This is the very serious condition as is referred to as caval syndrome. In this stage, the dog heartworm symptoms are characterized by heavy infestation of heartworms. A large mass of worms is found in blood, a situation that causes blockage of blood flowing back to the cardiac. This stage can be life threatening and requires surgical approach to remove the worms. The surgical procedure is risks and most of the dogs that suffer caval syndrome die even when the surgery is performed. However, not all dogs will develop this caval syndrome.

Heartworm life cycle

mosquito carrier of heartworm larvaeWhen the heartworms grow to adults, the females release offsprings known as microfilariae. These offsprings are released into the bloodstream of dogs and if a mosquito bites the infested dog, it is infected with these microfilariae. While living inside the mosquito, the microfilaria begins to develop into larvae. Under the right environmental conditions, they become infective larvae capable of infecting a host or dog.

The microfilariae will take about 10 to 14 days inside a mosquito to be able to turn into an infective form. One aspect with microfilariae is that they cannot become infective larvae without getting into the body of mosquitoes. When the larvae have become infective, they are passed or transmitted to another dog through a mosquito bite wound. In the newly infected dog, they stay there for quite a while. It may take about 6 to 7 months in the newly infected dog for the larvae to develop to adults worms. Adults begin to mate where the female worms release offspring in bloodstream and this completes the life-cycle.

Diagnosis of heartworm infection

The symptoms of heartworm infestation largely depend on the size of a dog and number of adult worms in the body of the dog. Usually dogs, which have low numbers of the worms or worm burden, will remain asymptomatic for some time meaning they may not show dog heartworm symptoms. This situation may hinder the early detection of worms giving them the chance to start multiplying thus causing harm to the dog. When there is substantial amount of adult worms to cause physiological changes in dog’s body, some of the early signs may start developing such as tiring easily and being intolerance to exercise.
There are different tests that can be done to detect the presence of heartworm infections and the most accurate is antigen test. This heartworm antigen test helps identify any antigen, which may have been produced by adult female worms. However, false test results may occur when diagnosing the dog heartworm symptoms in early stages of the infestations, if the larvae have not developed to adults. It may also occur when there is low worm burden or fewer adult heartworms.

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Similarly, the tests for antigens may turn false if only male worms are present. However, false positive results are uncommon. Thorough testing is essential to eliminate any doubts for other conditions like dog parvo symptoms.
Microfilarial concentration test may be performed and in this test, a blood sample is taken and examined of the presence of the parasites under a microscope. Again, there may be false positives in this test because about 10 to 25 percent of dogs infested with heartworms do not have the microfilariae circulating in peripheral blood meaning that the larvae may be present in body and not in the peripheral blood. When there is a heavy infestation in dogs, a chest X-ray may be done to determine the extent of heartworm disease and symptoms. This is perhaps the best test to help determine the severity of the infection. X-ray test can show enlarged right ventricle or pulmonary arties arising from heavy infestations of worms. Other tests that may be performed are ECG and echocardiogram. Blood and urine sample may also be obtained for further tests especially for infections, which have extended to the liver and kidneys.

Treatment of Dog Heartworm Symptoms

dog tirednessTreatment of dog heartworm symptoms depends on a number of factors and one is the location of infestation in the dog’s body and any health complications that may be inherent such as lung or heart failure and kidney or liver disease. If the condition is mild or moderate meaning low infestations, the veterinarian will carry out dog heartworm treatment to eliminate all adult worms and destroy any larvae or microfilaria that may be present. It is essential that when medication is being done, complications of drug toxicity be avoided. There may also be complications of passing dead worms into lungs, which can be fatal. Veterinarians will examine the treatment approach to go for such as eliminating the microfilaria first and then moving on to get rid of adult heartworms.
You need to discuss with the veterinarian on the most appropriate mode and method of treatment of dog heartworm symptoms. In eliminating adult worms, mainly two drugs that have been approved by FDA, and they are melarsamine and thiacetarsamide. If a veterinarian recommends medication with Caparsolate or thiace tarsamide, the drug is administered intravenously meaning injecting it directly into veins. This drug is given two times a day and for a period of two days. There may be some side effects or toxic reactions when using Caparsolate as one of the dog heartworm treatment options and they include vomiting, loss of appetite, jaundice, diarrhea, kidney failure or even death. In addition, Caparsolate may not eliminate all the heartworms especially the immature ones because they tend to be resistant to the drug. Therefore, it may require treatment with Caparsolate to be followed by another medication for microfilariae. Similarly, dogs at higher health risks especially those with dog heartworm symptoms like liver, heart and kidney complications may not be suitable to use this drug.

Melarsamine drug a lower health risk Immiticide

Immiticide on is capable of eliminating about 90% of the worms and this makes it a more effective drug than Caparsolate. In addition, immiticide or melarsamine drug has relatively lower health risks and could be administered to dogs with problems in heart, liver or kidneys but with close supervision by a veterinarian. This dog heartworm medicine is given through intramuscular injections once in a day for a period of two days or depending on the severity of the infection. For seriously ill dogs, especially those with caval syndrome, a surgical removal may be recommended. Such dogs are not good candidates for drug treatment because of side effects such as liver and kidney failures as well as thromboembolism.

Followup heartworm antigen test

A heartworm antigen test may be required after the treatments particularly within 3 to 5 months to determine if the drugs administered were effective in eliminating the dog heartworm symptoms. If the test turns positive, a retreatment may be opted to get rid of the remaining worms. When the adult worms have been killed through drugs, the next treatment is aimed at killing circulating microfilariae or larvae. The veterinarians may wait for several weeks to allow for dog heartworm treatment recovery from effects of previous therapy before they administer microfilariae treatment. Of the drugs used in treating microfilariae, ivermectin is the most effective and has fewer side effects in dogs that do not show sensitivity in drugs. Apparently, none of the microfilariae treatment drugs have been licensed for use.

Dog Heartworm Symptoms Prevention of Dog Heartworms

Prevention is the best way of controlling heartworm disease. Keeping your dog away from mosquito bites may be the best dog heartworm prevention measure, but this is not 100 percent practically attainable. To reduce the chances of your dog being bitten by mosquitoes, it should remain indoors in late afternoons and evenings. This is the time when these insects actively feed on your dog. You can also spray the yard as well as remove stagnating water to reduce the breeding of mosquitoes but then again this may never eliminate the problem. A heartworm-prevention program with the use of dog heartworm prevention pills may be devised in areas prone to this disease. In addition, antigen test may be repeated on an annual basis or as recommended by a veterinarian to examine dog heartworm symptoms.

Causes of heartworms and treatments for dogs.

Here is a great resource guide (pdf) for you to check out about dogs that have been infected with Heartworms. It is from the Houston Collie Rescue located in Stafford, TX. and is titled “Heartworm Treatment Aftercare“.  The following is a excerpt from the guide:


In severe cases, the worms grow, reproduce, and migrate from the heart to arteries, the lungs, and even other organs in the body. It is a horrific disease that no dog should have to endure and is completely preventable by heartworm pills, which kill the microfilaria deposited in the blood stream by mosquitoes before they can invade the heart, mature, consume the heart, and kill the dog.




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