Canine heartworm, Dirofilaria immitis


Canine heartworm, Dirofilaria immitis, is a significant health risk for dogs, causing severe and potentially fatal disease. The parasitic nematodes are transmitted by mosquitoes, more than 60 different mosquitoes of various genera act as intermediate hosts. Dirofilariosis is worldwide distributed and occurs especially in warmer climatic zones, spreading across Southern Europe and the Americas at an alarming pace. This effect seems to be related to global warming expanding the activity season of vector mosquitoes, but also increased human mobility and “traveling” pets. The adult stages of the parasitic nematode are up to 30 cm long in dogs, live up to 7 years and reside in the pulmonary arteries and in the right ventricle of the heart.

Treatment of dirofilariosis is problematic, because approved drugs (arsenical melarsomine dihydrochloride) can cause adverse neurological reactions. Treatment also carries a significant risk of lethality due to pulmonary thromboembolism (blockage of the pulmonary artery by dead nematodes). To this day no vaccines are available. These issues prompted the American Heartworm Society to recommend year-round chemoprophylactic treatment for dogs. This requires monthly topical or oral administration of anthelmintics, predominantly macrocyclic lactones. However, not all dog breeds tolerate these chemotherapeutics which cross the blood-brain barrier and cause severe adverse effects.

A major problem in heartworm prevention is increasing resistance formation against anthelmintic drugs. An important reason for lack of efficacy of heartworm prevention and resistance formation is owner compliance. The high frequency of drug application which is required for heartworm prevention is prone to failures; regular treatment may often be interrupted. Failure of owner compliance to maintain regular monthly preventative therapy is estimated at 10-20%.

The current costs for heartworm prevention are very high (60-100 $/dog/year), which is another drawback in the fight against heartworm disease. More cost-efficient, less labor-intense and more efficacious methods are urgently needed.


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