Heartworm disease in dogs

In humans and animals, especially in tropical areas, filaria are helminths, parasitic worms, of various organs: skin, lymphatic channels, eyes, heart and are responsible for often serious disorders. You will know about heartworm disease in dogs.

Heartworm disease known as heartworm disease is a serious filariasis in dogs caused by Dirofilaria immitis . It sometimes affects humans: it is a zoonosis.

Known throughout the world, it concerns in France the hot areas of the Mediterranean rim from the Maritime Alps to the Pyrénées-Orientales but the epicenter is located in the Camargue, Corsica and Overseas.

Parasite and transmission

Dirofilaria immitis , responsible for the disease is a nematode, a smooth white worm, without segmentation measuring a dozen centimeters for the male and twenty for the female for a millimeter in diameter.

The disease is transmitted by several species of mosquitoes which ingest larvae (microfilariae) during their meals on an infected dog. After a maturation period of 15 days in the insect, these larvae, which have become infesting, transmits through sting to another dog. They then migrate to the pulmonary arteries and the heart where they become adults and in turn give birth to larvae which are scattered throughout the bloodstream. This cycle lasts about six months in dogs.

The expansion of certain mosquitoes, including the tiger mosquito, and the increase in average temperature favorable to vectors explain an increase in the areas where the disease is rife. Country, hunting and herding dogs are more concerned than city dwellers.

Symptoms of heartworm disease in dogs

If the Dirofilaria parasite has been known since 1856, control of the disease (diagnosis, treatment, prevention) dates from the 1990s.

The symptoms observed are a result of the mechanical action and the amount of worms present in the heart. They worsen over time and are classified into four phases.

In phase I, there are no symptoms for sometimes several years. Then appears an alteration of the general state (phase II) with fatigue, irregular cough and weight loss. Finally in phase III, these symptoms worsen: the effort becomes difficult and then impossible, the cough sets in and breathing is painful (dyspnea), the weight loss intensifies, the appetite decreases. Anemia and a distended belly, characteristic of the presence of ascites (intra-abdominal fluid), appear as well as edema of the limbs. These signs correspond to pulmonary hypertension then to right heart failure (worms in the right ventricle and pulmonary artery) and finally to global heart failure suddenly decompensating (phase IV) shortly before the patient’s death.

Sometimes there are signs of pulmonary embolism, with one or more worms obstructing a pulmonary vessel. There is then a sudden respiratory distress, sometimes a coughing up blood (hemoptysis). Embolisms in other vessels are possible.

Heartworm disease in dogs


The observed cardiopulmonary signs may correspond to several diseases. It is necessary to specify their origin.

If these symptoms observed in places where the disease is rife are any clue, the laboratory confirms their origin. The biochemical assessment of the liver (liver enzymes), kidney (urea, creatinine) and hematology (count and formula of blood cells, platelets) is not specific but it helps to decide on the treatment. Finally, we can precisely identify the circulating larvae (microfilariae) in the blood stream.

Immunological tests will make it possible to confirm the presence of adult worms, with high specificity and high sensitivity. Easy to perform, they give immediate results.

Radiography, ultrasound and other more sophisticated techniques are useful in determining the fate of the patient.

Once the diagnosis has established which treatment should apply?

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Treatment of heartworm disease

Specific treatment aims at destroying adult worms and microfilariae.

At stage IV only a surgical intervention could propose to remove the worms.

In advanced stage III, the prognosis reserves and the treatment sometimes risky. It is vital to leave the patient at absolute rest. The only effective drug is melarsonamine (IMMITICIDE®), by intramuscular injection, twice 24 hours apart. The destruction of adult filaria sometimes causes complications: embolism already considered; the release of bacteria living in symbiosis with the worm, the Wolbachia responsible for inflammatory phenomena, sometimes state of shock. Complementary treatments are then necessary: ​​antibiotics (cyclins, cephalosporins), antihistamines, anti-inflammatory drugs, etc. Finally, corrective treatment for the symptoms observed must implement.

In the less severe phases, the causal treatment is the same, and the associated treatment lighter. In phase II, and a fortiori I, the prognosis is favorable. The disappearance of the parasites will be checked by an immunological test at two and three months.

Given the severity of the disease, an early diagnosis should make, if possible before the first clinical signs, and the advantages and disadvantages of the treatment should be carefully weighed.

Prevention of heartworm disease

It is necessary to carry out a detection test.

If it is negative, it is imperative to set up a prophylaxis in the regions where the disease is rife or for dogs who stay there temporarily. Milbemycins (moxidectin) or selamectin are used. These specialties, orally or in spot-on (in pipettes) must be used every month with regularity, before the departure in an enzootic zone and up to one month after the return.

As far as possible, we must also fight against vectors and mosquitoes.

In practice

Heartworm disease is serious when it becomes apparent. If you cannot sometimes treat it, Better to prevent it. Talk to your veterinarian who can, before any sign, in a routine consultation or at an early age perform a screening test.

If you live in a risk area, he will offer you prophylaxis and, if necessary, discuss treatment with you.

For those of you who are going on vacation in the South, he will tell you the risk and if necessary will put in place a prevention.

In all cases, find out, the risk is very real and the areas concerned are increasing.