Sparganosis

Sparganosis is a parasitic infection caused by the plerocercoid larvae of the genus Spirometra including S. mansoni, S. ranarum, S. mansonoides and S. erinacei. It was first described by Patrick Manson in 1882, and the first human case was reported by Charles Wardell Stiles from Florida in 1908. The infection is transmitted by ingestion of contaminated water, ingestion of a second intermediate host such as a frog or snake, or contact between a second intermediate host and an open wound or mucous membrane. Humans are the accidental hosts in the life cycle, while dogs, cats, and other mammals are definitive hosts. Copepods (freshwater crustaceans) are the first intermediate hosts, and various amphibians and reptiles are second intermediate hosts. Once a human becomes infected, the plerocercoid larvae migrate to a subcutaneous location, where they typically develop into a painful nodule. Migration to the brain results in cerebral sparganosis, while migration to the eyes results in ocular sparganosis. Sparganosis is most prevalent in Eastern Asia, although cases have been described in countries throughout the world. In total, approximately 300 cases have been described in the literature up to 2003. Diagnosis is typically not made until the sparganum larva has been surgically removed. Praziquantel is the drug of choice, although its efficacy is unknown and surgical removal of the sparganum is generally the best treatment. Public health interventions should focus on water and dietary sanitation, as well as education about the disease in rural areas and discouragement of the use of poultices.

Symptoms Clinical presentation of sparganosis most often occurs after the larvae have migrated to a subcutaneous location. The destination of the larvae is often a tissue or muscle in the chest, abdominal wall, extremities, or scrotum, although other sites include the eyes, brain, urinary tract, pleura, pericardium, and spinal canal. The early stages of disease in humans are often asymptomatic, but the spargana typically cause a painful inflammatory reaction in the tissues surrounding the subcutaneous site as they grow. Discrete subcutaneous nodules develop that may appear and disappear over a period of time. The nodules usually itch, swell, turn red, and migrate, and are often accompanied by painful edema. Seizures, hemiparesis, and headaches are also common symptoms of sparganosis, especially cerebral sparganosis, and eosinophilia is a common sign. Clinical symptoms also vary according to the location of the sparganum; possible symptoms include elephantiasis from location in the lymph channels, peritonitis from location in the intestinal perforation, and brain abscesses from location in the brain. In genital sparganosis, subcutaneous nodules are present in the groin, labia, or scrotum and may appear tumor-like. Ocular sparganosis a particularly well-described type of sparganosis. Early signs of the ocular form include eye pain, epiphora (excessive watering of the eye), and/or ptosis (drooping of the upper eyelid). Other signs include periorbital edema and/or edematous swelling that resembles Romana's sign in Chagas disease, lacrimation, orbital cellulitis, exophthalmos (protrusion of the eyeball), and/or an exposed cornea ulcer. The most common sign at presentation is a mass lesion in the eye. If untreated, ocular sparganosis can lead to blindness. In one case of brain infestation by Spirometra erinaceieuropaei, a man sought treatment for headaches, seizures, memory flashbacks and strange smells. Magnetic resonance imaging (MRI) scans showed a cluster of rings, initially in the right medial temporal lobe, but moving over time to the other side of the brain. The cause was not determined for four years; ultimately a biopsy was performed and a 1 cm-long tapeworm was found and removed. The patient continued to have symptoms.

Transmission The parasite is transmitted to humans in three different ways. First, humans may acquire the infection by drinking water that is contaminated with copepods housing Spirometra larvae. Second, humans may acquire the infection by consuming the raw flesh of one of the second intermediate hosts, such as frogs or snakes. For example, humans consume raw snakes or tadpoles for medicinal purposes in some Asian cultures; if the snakes or tadpoles are infected, the larvae may be transmitted to humans. Third, humans may acquire the infection by placing raw poultices of the second intermediate hosts on open wounds, lesions, or the eyes for medicinal or ritualistic reasons. If the poultice is infected with plerocercoid larvae, the human may become infected. According to Zunt et al., human infection most often occurs following ingestion of infected raw snake, frog, or pig, although contact with infected flesh of an intermediate host can also cause infection. The high prevalence in Korea may be explained by the ingestion of dog meat. In the Western hemisphere, the most common cause of infection is drinking contaminated water.

Hosts, reservoirs, and vectors Definitive hosts of Spirometra include dogs, cats, birds, and wild carnivores, while humans are accidental hosts. First intermediate hosts include copepods and other fresh-water crustaceans, while second intermediate hosts include birds, reptiles, and amphibians. The intermediate hosts are also the reservoirs of Spirometra. There are no vectors of Spirometra.

Incubation period The incubation period of Spirometra is 20 days to 3 years.

Morphology The sparganum larvae are white, wrinkled, and ribbon-shaped. They range from a few millimeters in length to several centimeters. The anterior end can invaginate and bears suggestions of the sucking grooves that are present in the scolex of the mature worm. The absence of a scolex or protoscolex in Spirometra is a key difference in differentiating between Taenia solium and Spirometra. The worm's body is also characterized by a stromal network of smooth muscle. In general, plerocercoids in the East (S. mansoni) are described as larger and more delicate than those in the West. The eggs of S. mansonoides provide an example of the general morphological characteristics of Spirometra eggs. S. mansonoides eggs resemble the eggs of D. latum, with some specific differences. S. mansonoides eggs measure 57-66 μm by 33-37 μm, which is smaller than the eggs of D. latum. The eggs of S. mansonoides are also ellipsoidal and have a conical, prominent operculum.

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