What are Helminths?

Helminths are parasitic worms that cause a wide variety of infectious diseases, some of which involve the musculoskeletal system. Helminths may be classified into nematodes or roundworms, trematodes or flatworms, and cestodes or tapeworms.

Hookworm disease is caused by Ancylostoma duodenale or Necator americanus.

Loiasis, or African eye worm disease, is produced when the filaria Loa loa become deposited in the victim's skin after the bite of the mango fly and burrow into the deeper subcutaneous tissue. Calabar swellings represent localized areas of allergic inflammation found especially in the forearm. The dead worms cause abscesses or undergo calcification.

Filariasis is produced by the adult worms of the species Wuchereria bancrofti or Brugia malayi, which localize in the lymphatic and soft tissues of the human body. Loiasis and onchocerciasis (caused by Onchocerca volvulus) are also forms of filariasis. Eventually filariasis can lead to massive lymphoedema or elephantiasis, especially of the legs and the scrotum. An affected limb may be greatly enlarged and show soft tissue thickening, blurring of subcutaneous fat planes, soft tissue calcification and a linear striated pattern on radiographs.

Dracunculiasis is an infectious disease caused by the guinea worm (Dracunculus medinensis), often after ingestion of water contaminated with the vector, a water flea. Radiographic abnormalities are produced in the lower extremities and hands by calcified dead parasites within the subcutaneous tissues. Long, curled radiodense shadows are observed. Presence of a guinea worm adjacent to a joint may lead to a reaction with joint effusion and secondary bacterial infection.

Cysticercosis occurs when the larval form of the Taenia solium tapeworm, Cysticercus cellulosae, becomes deposited in muscle, subcutaneous tissue, various visceral organs (heart, brain, lung, liver) and the eye. A foreign body reaction followed by caseation and calcification may occur when the larvae die. Radiographs reveal elongated calcifications with the long axis of the calcified cysts lying in the plane of the muscle bundles.

Echinococcosis is caused principally by the larval stage of Echinococcus granulosus. Larval cysts may develop in various viscera, particularly the liver and the lungs, and may calcify, producing irregular curvilinear, eggshell-like cystic radiodense areas. Bone lesions may also occur, principally in the vertebral column, pelvis, long bones, and skull. Radiographically, the expansile cystic osteolytic lesions may reveal cortical violation and formation of a soft tissue mass with calcification. CT scanning shows a soft tissue mass adjacent to sites of bone involvement. On MR images, numerous cystic lesions of high signal intensity in T2-weighted spin-echo sequences are characteristic. Pathologic fracture, secondary infection, rupture into the spinal canal, transarticular extension and intrapelvic extension sometimes occur.

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Last Updated: Feb 10, 2010

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