111 - Heartworm and Related Nematodes

Abstract

•First Described: Heartworm was first described in dogs in Italy in 16261 and in the United States in 1847.2•Cause: Dirofilaria immitis, belonging to the superfamily Filarioidea and family Onchocercidae. A related nematode, Dirofilaria repens, is found in southern and central Europe, Africa, and Asia but is not currently endemic in North America.•Affected Hosts: Although canids (domestic dogs, coyotes, foxes, wolves, and other wild canids) are the definitive hosts for heartworms, the parasite has been found in more than 30 species of animals, including domestic cats and wild felids, bears, ferrets, seals, sea lions, and humans.•Intermediate Hosts: There are multiple mosquito vectors in every region of the United States. More than 70 species of mosquitoes have been shown to be capable of transmitting heartworms; 25 species have been proven to be significant vectors.•Geographic Distribution: Heartworms are endemic in North, Central, and South America; the Caribbean Islands; the coastal regions of Africa, southern Europe, and Asia; Japan; Indonesia; and Australia.•Route of Transmission: Female mosquitoes feeding on a microfilaremic canine host ingest microfilariae. The ingested microfilariae undergo a transformation and two molts over a 2- to 4-week period to become infective third-stage larvae (L3). The L3 are then deposited on a dog’s skin in a droplet of hemolymph by a feeding female mosquito. The L3 enter through the bite wound into the subcutaneous tissue.•Major Clinical Signs: Signs of heartworm disease can range from a cough and exercise intolerance to dyspnea, abnormal heart and lung sounds, hepatomegaly, syncope, ascites, and death.•Differential Diagnoses: These include primary pulmonary diseases (pneumonia, chronic bronchitis, allergic lung disease), pulmonary thromboembolism, pulmonary hypertension, and right-sided heart failure.•Human Health Significance: Dirofilaria immitis is of public health concern even though the number of reports of infection in humans is relatively small. The most common clinical syndrome reported in human infections is the formation of a pulmonary nodule or nodules within the lung parenchyma.