Heart worm



The transmission of heart worm (dirofilariosis) occurs via various mosquitoes. In this process, a mosquito transmits the pathogen (larvae) to the dog during the sucking act. Transmission from dogs to humans is not known. Infection of a human through the bite of a mosquito is unlikely. 


The causative agent of dirofilariasis is a specific filarial species called Dirofilaria immitis. The larvae, also called microfilariae, are already formed in the vector, the mosquito, and are transmitted to the host, the dog. After transmission, they settle on the heart and in the artery leading to the lungs, where they develop into adult parasites, the macrofilariae, after no later than four months. These heart worms grow to a thickness of about 1 mm, and reach a length of up to 30 cm. About 6 months after infection, the females produce microfilariae, which enter smaller blood vessels with the blood and may be reabsorbed by mosquitoes during the sucking act.

They settle mainly in the right side of the heart, the large pulmonary artery and the sections of the vena cava close to the heart and cause severely limiting symptoms.

Incubation Period

Between a few weeks and, in rare cases, years. Infestation cannot be detected until at least six months after transmission. 


In fact, infections are often inconspicuous. In other cases, the first symptoms may develop only about six months after infection, i.e. when the worms mature. Infestation manifests as shortness of breath, cough, anemia, decreased performance, palpitations, liver congestion and weight loss. 


The microfilariae, the larvae, are detected in most cases with the help of a so-called Knott test.
In contrast, the macrofilariae, the adult heartworms, can be detected by an ultrasound examination of the heart and an X-ray examination. In addition, antigen detection in serum (ELISA test) provides information about an infestation. This kind of test can be done at the earliest six months after infection. 


Filariae can be completely treated and controlled. Microfilariae are normally treated with spot-on preparations, while macrofilariae are primarily treated with Immiticide® injections, as well as “Doxycyclin”, “Ronaxan”. Depending on the progress of the infestation, this disease can be fatal.