Causal Agents:Cestodes in the genus Spirometra, including S. mansoni, S. ranarum, S. mansonoides and S. erinacei, as well as the aberrant Sparganum proliferum.

Life Cycle:

Adult members of the genus Spirometra live in the intestines of dogs and cats .  Eggs are shed in feces and embryonate in the environment .  Eggs hatch in water and release coracidia , which are ingested by copepods.  The coracidia develop into procercoid larvae in the copepod intermediate host .  Second intermediate hosts, including fish, reptiles and amphibians, ingest infected copepods and acquire procercoid larvae.  The procercoid larvae develop into plerocercoid larvae in the second intermediate host .  The cycle is completed when a predator (dog or cat) eats an infected second intermediate host .  Humans cannot serve as definitive hosts for Spirometra spp., but serve as paratenic or second intermediate hosts and develop sparganosis.  Humans acquire sparganosis by either drinking water contaminated with infected copepods or consuming the flesh of an under-cooked second intermediate or paratenic host.  Spargana can live up to 20 years in the human host.

Geographic Distribution:The genus Spirometra occurs worldwide in distribution, although most human cases of sparganosis are recorded from southeast Asian countries.  Sparganosis is endemic in animals throughout North America, although human cases from this area are rare.

Clinical Features:Migrating spargana cause various symptoms depending on the final location in the host.  Spargana may locate anywhere, including subcutaneous tissue, breast, orbit, urinary tract, pleural cavity, lungs, abdominal viscera and the central nervous system.  The migration in subcutaneous tissues is usually painless, but when spargana settle in the brain or spine a variety of neurological symptoms may occur, including weakness, headache, seizure, and abnormal skin sensations, such as numbness or tingling.  If the inner ear is involved, the patient may experience vertigo or deafness.  Occasionally, Sparganum proliferum can cause

proliferative lesions in the infected tissue, with multiple plerocercoids present in a single site.

Laboratory Diagnosis:Diagnosis is usually made by the recovery of a sparganum from infected tissue.  The presence of a sparganum is diagnostic and identification to the species level is usually not warranted.  However, the best way to identify the species is to infect an appropriate definitive host with a living sparganum and identify the adult after maturation.

Diagnostic findings

Microscopy

Treatment:The immature forms of Spirometra spp. are resistant to praziquantel and mebendazole, and currently there is no recommended drug therapy for sparganosis.  Surgical removal of the complete sparganum is the best treatment.

Microscopy

Sparganosis is infection by the third-stage plerocercoid larva (sparganum) of pseudophyllidean cestodes of the genera Spirometra and Sparganum, the latter of which may be an aberrant Spirometra sp.  The definitive hosts for Spirometra spp. are canids and felids, and humans serve as only paratenic or second intermediate hosts for the parasites.  Spargana can be found in many organs in the human host, including the pleural cavity, eyes, pericardium, abdominal cavity and viscera, and the central nervous system.

A B

A, B:  Proliferating spargana in groin tissue of a patient from Paraguay, stained with hematoxylin and eosin (H&E).

C D

C: Proliferating sparganum in lung tissue in a patient from Taiwan, stained with hematoxylin and eosin (H&E).D: Higher magnification of the sparganum in Figure C.  In this image, calcareous corpuscles (green arrows) can be seen.

E F

E: Sparganum removed from the chest wall of a patient.  The worm measured about 70 mm long.  Image from a specimen courtesy of the Oklahoma State Department of Health.F: Sparganum removed from the ocular conjunctiva of a patient from Taiwan.  The worm measured 40 mm long.  Image courtesy of Dr. John H. Cross and the Uniformed Services University of the Health Sciences, Bethesda, MD.