200 Years. 200 Stories. Story 14: “Heartworm Attack ”

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illustration of a nematode parasite
Joseph Leidy's illustration of a nematode parasite of the bullfrogArchives Coll. 12 D box 4 vol. 5

Heartworm Attack

Joseph Leidy, the father of American Vertebrate Paleontology, did not limit his research to fossils. Two years before he described Hadrosaurus foulkii, the most complete dinosaur skeleton known in 1858, he identified heartworm, a serious parasitic disease that affects dogs and some other mammals. He described the culprit, a nematode worm, and named it Filaria immitis. (It was later renamed Dirofilaria immitis.)

Leidy related the circumstances leading up to the discovery: “Mr. Joseph Jones recently presented to me two specimens of the heart of the dog.” According to Leidy, one dog's heart contained five filariae (the long, thread-like adults). In the second dog, “the right auricle and ventricle, and the pulmonary artery in its ramifications through the lungs are literally stuffed with Filariae.” Leidy noted that the blood of the second dog contained “a great number of the young.”

Leidy noted that the first dog had an appetite that was “voracious and insatiable, and notwithstanding he was abundantly supplied with food, he remained in a very lean condition.” The dog afflicted with the mass of worms “was always so thin as to resemble a skeleton.”

Thanks to Leidy's identification of heartworm, scientists have created medications to treat it. Want to know more about Leidy? See the online exhibit on Joseph Leidy or visit the Academy to see Hadrosaurus foulkii in our Dinosaur Hall!

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