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What is Dirofilariasis? How can we protect our dog?

Dirofilariasis is a parasitic disease widespread in the world!

The infected species are dog, cat, ferret, fox, wolf, seal horse. The man can rarely be accidental host and Dirofilaria immitis can not complete its cycle of development to adult parasite. The spread depends on the one hand, of the population of the reservoir host (usually a dog), which ends the life cycle of the parasite and is prepared mikrofilaremiya, and on the other hand by the mosquito population, where they develop early larval stages.

The disease is caused by Dirofilaria immitis. Adult worms with a length of 17-27 cm normal parasites in the pulmonary artery and right atrium. Microfilariae (long about 315 μm) are found in the bloodstream and live 1-3 years. Microfilariae are ingested by the mosquito during feeding. In the mosquitoes they ripe into larvae third degree (L3) for 8-28 days, depending on outside temperatures. After that the mosquitoes can infect by bite another animal. One mosquito can carry 10-12 larvae. In the infected dog for six months L3 ripes into L4 and L5 and turn into adult parasites. The L5 larvae are 1-2 cm long and may cause clinically manifested disease in their movement at the distal ends of the pulmonary arteries where they ripe. Dogs with a large number of migratory L5 may begin to cough 2-3 months before mikrofilaremiya or could be found antigens in the blood stream. The diagnosis in such cases is difficult. 6-7 months after invading, the dog develops mikrofilaremiya if there are adult worms – male or female. In about 10% of cases the mikrofilaremiya induces a powerful immune response  that could destroy the microfilariae. The adult worms live in the heart 3-5 years. While they are alive they rarely cause endarterit and embolization. However, they cause a violation of hemodynamics, increased blood pressure, right ventricular hypertrophy and right heart failure. These changes are stronger in physically active dogs. In sporting and working dogs can be cause a severe pathology, even with a small number of parasites.

Clinical signs

Many dogs with heartworm disease are asymptomatic! Visibly sick animals get tired easily, weaken, develop  asthma, especially after exercise, coughing, often with blood in sputum. The cough is the main clinical sign. A main factor in the disease are adult parasites which are found in pulmonary arteries and right side of the heart. But in some cases individual parasites can cause embolism of the arteries in the brain, eye, and other organs, which leads to relevant organ diseases.

In mechanical obstruction of the tricuspid valve or due to the development of cor pulmonale could be develop signs of right heart failure. During auscultation there are abnormal lung sounds (mostly wet wheezing), stronger and often split second heart sound, cardiac noise associated with tricuspid valve, cardiac arrhythmias. It can be observed ascites, hepatomegaly, icterus, liver and kidney dysfunction. Upon occlusion of the vena cava by parasites, which is obtained upon more than 60 adult worm, very often develops expansion and pulsation of jugular veins (retrograde venous pulse) disseminated intravascular coagulation and death by 24-72 hours due the cardiogenic shock. This condition is called vena cava syndrome (caval syndrome). Vena cava syndrome need to differentiate from the severe form of the disease without obstruction  to assess whether it is necessary or not surgery. The obstruction of vena cava can be proved most accurately by ultrasound.


Treatment is difficult, costly and lies quite risks. It is possible that patients in the advanced stage of the disease to be treated, but the likelihood of complications and even death is very large! That is why prevention against this disease is the best solution!


Veterinary clinic „Sofia“ offers initiative for the prevention of heartworm disease!

It is good before instituting preventive scheme to test for the presence of heartworms in the blood. It is best to do 1-2 times per year. It is advisable to start the program from 8 weeks of the puppies life. There are several options for administration, depending on the preference of the owner.