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Filariasis or heartworm of the dog is caused by the infestation of the animal by a parasite that is carried inside it, through the bite of a mosquito.

ATTENTION: cats are also at risk of heartworm

Depending on the type of parasite introduced, the disease can develop in two ways.

The first caused by the parasite Dirofilaria repens which remains localized in the skin, the second and more serious, that caused by Dirofilaria immitis which affects the cardiopulmonary system.

Heartworm  disease in dogs

Also called  cardiopulmonary dirofilarisosis , it is a serious disease that affects dogs of any breed, gender and age.
A majority of cases have been verified in large-sized males living mainly outdoors rather than small-sized ones living at home.
The disease is caused by a parasite from the nematode family, or roundworms, called  Dirofilaria immitis . The adult parasite can reach considerable dimensions: 12-17 cm the male, 25-32 the females.

, Filariasis or Filaria, Nuova Fattoria Pet Food

The disease has spread mainly in Northern Italy , in particular throughout the Po Valley , in the areas around the Po and in the lake areas .
In recent times there have been cases of disease and unfortunately they are constantly increasing, also in other geographical areas: such as Tuscany , the flat and coastal areas of Sardinia and in some areas of Sicily and Campania .

Transmission of the disease

The transmission of the disease occurs through the bites of common mosquitoes and / or even the tiger mosquito , which are simply the vehicle of the worm larvae.

Cycle of contagion

We can summarize the heartworm infection cycle in six phases

F1 : the mosquito bites an infected animal and by sucking its blood ingests the larvae of heartworm in their first stage of growth (micro-filaria).

 F2 : In about a week the larvae mature inside the mosquito and are ready for the next stage.

F3 : in another seven days the larvae develop further evolving to the infesting form.

F4 : The parasite enters the circulatory system of the new host animal reaching up to the capillaries when it is bitten by a heartworm-carrying mosquito. In about 10 days the larvae further evolve taking the final round worm shape.

, Filariasis or Filaria, Nuova Fattoria Pet Food

F5 : In the new host animal, the larvae of the parasite  Dirofilaria immitis   once they become worms enter the circulatory system and settle in the vicinity of the heart and lungs, causing heart and respiratory problems. They grow and spread massively so that, if the disease is not diagnosed and treated in time, it can lead to the death of our animal. The adult worms of  Dirofilaria Repens larvae , on the other hand, go to localize in the subcutis, causing much less damage.

F6 : Adult worms can reproduce and release micro-filariae into the dog’s circulatory system; the micro-filariae (first evolutionary stage) reach the capillaries where they infest another mosquito while sucking the blood and the cycle begins again. After reproducing, the worm dies, but the infected dog has suffered serious damage.


  • Itching
  • Presence of subcutaneous nodules
  • Decreased appetite
  • Tiredness, exercise intolerance
  • Dry cough especially after exercise
  • Anemia

Preventive interventions

  • minimize the chances of the mosquito coming into contact with our dog through repellent substances.
  • At night, during periods in which mosquitoes are present, it is advisable, as far as possible, to keep our friends indoors, possibly protected with mosquito nets.
  • After consulting the veterinarian, treat our dog constantly with drugs that act by inhibiting the development of adult parasites; this treatment is called  micro-filaricide therapy: this therapy is a real cure to prevent the micro-filaria from evolving into an adult parasite. This type of treatment should be undertaken in the period from April to December inclusive. The treatment can be undertaken on animals that are at least 6 weeks old.

In animals that have never undergone prophylaxis treatments, it may be appropriate to perform a test for the detection of heartworm antigens: a simple, slightly invasive and painless test that is performed by taking a few drops of blood.

In conclusion

In the prevention of Filariasis as for Leishmaniasis , prevention is a must but it cannot exempt us from subjecting our animal to a visit to a veterinarian, who will be able to verify through simple clinical tests what the real state of health of the animal is, in the in case of contagion, he will be able to intervene immediately and in any case he will show you which prevention system is most suitable for your animal.

As always, we remind you that this article, like all the others published on our site, has the simple purpose of making our readers aware of some issues related to the world of pets and does not in any way pretend to replace the judgment and opinion of a veterinarian. , which must always and in all circumstances be consulted.

The Staff of Nuova Fattoria Srl