The first documented case of human Dirofilaria infection occurred in 1887 by de Magalhaes, who reported a subcutaneous infection in a male child from Brazil.  In the United States, the first case of subcutaneous dirofilariasis to be reported occurred in 1941 in New Orleans, in which Dirofilaria infection was discovered in a female cadaver (Shah).  Before this, although D. immitis was known to be the infectious agent of dog heartworm, it was not thought that members of the genus, Dirofilaria, were capable of infecting humans.
    The first case of human pulmonary dirofilariasis was not reported until 1961 (Shah).  Before this (mainly in the 1950s), chest x-ray examinations showed pulmonary nodules in many patients, which were misdiagnosed as carcinomas.  Surgical resection of these nodules revealed immature filariae within the nodules.  When these cases were later reviewed, the filariae were identified as D. immitis.