Sparganosis is an infection by the plerocercoid larvae of various diphyllobothroid tapeworms belonging to the genus Spirometra. It is similar in morphology and life cycle to the fish tapeworm, Diphyllobothrium latum. Sparganosis is reported sporadically around the world; a higher prevalence of the disease occurs in several Asian countries.
Sparganosis, of the genus Spirometra, is a Pseudophyllidean tapeworm. There are several species of Spirometra, including S. mansoni, S. mansonoides, S. erinacei, S. ranarum, S. decipiens, S. houghtoni, S. proliferum
The larvae are often referred to by the generic name Sparganum, because this stage was previously thought to represent a separate genus.
History of Discovery:
The genus Sparganum was originally described by Diesing in 1854. Manson reported the first human case of sparganosis in China in 1882, caused by Sparganum mansoni, the predominant species in Asia. In 1935, Mueller described Spirometra mansonoides, which is the predominant species in the United States. The first case of infection of the nonproliferative form of S. mansonoides was reported by Moore in 1914, and the first case of infection due to the proliferative form was reported by Stiles in 1908.
The clinical manifestations of sparganosis depend on which organs or tissues are involved. Subcutaneous tissues are most likely to be infected by the parasite, but visceral organs and the orbit of the eye, and rarely, the brain. The early migratory stages in the development of the sparganum are asymptomatic, but when it has reached its final site and begins to grow, its presence elicits a painful inflammatory reaction in the surrounding tissues. Sparganosis can cause intestinal obstruction, and the parasite has been recovered from the wall of the intestine, the breast, the scrotum, the epididymis, ureter, urinary bladder, abdominal cavity, heart, and lung.
The larval worms usually grow into irregular nodules (1 to 2 cm in diameter) and surround tissues, becoming edematous and painful. These nodules may persist for months or even years without any symptoms then suddenly become painful. Some patients complain of migratory nodules that come and go for many years.
Ocular sparganosis produces an especially intense reaction, with periorbital edema. Ocular sparganosis may result in blindness, as the parasite migrates to the conjunctiva and enters the orbit. In the orbital tissues, the larva is located in the posterior pole, producing inflammation that results in exophthalmia and lagophthalmia, which in turn, causes ulceration of the cornea. Ocular sparganosis causes intense pain, irritation, excessive lacrimation, and marked swelling of the eyelids.
Cerebral sparganosis is characterized by seizures, fatigue, confusion, headaches, memory loss, coma, fever, paresthesias, hemiparesis, motor weakness and other CNS symptoms. Cerebral sparganosis most likely involves the cerebral hemispheres, especially the frontoparietal lobes, in some cases extends to the cerebellum. The disease may appear as a massive cerebral hemorrhage.
Proliferative sparganosis, caused by S. proliferum, begins with a subcutaneous tumor in the thigh, shoulder, or neck, and eventually spreads to other parts of the skin, the muscles, and the internal organs, such as the lungs, abdomen, and brain. Nodules may open because of ulceration or scarification. Infection progresses over 5 to 25 years, and is fatal in all reported cases.
Sparganum infection occurs by three major routes. Infection is acquired by drinking water contaminated with copepods infected with the procercoid larval stage of the parasite. The larva penetrates the gut wall and moves to the muscles or subcutaneous tissues, where it grows into the Sparganum larva. The larva may then migrate to the subcutaneous tissues.
Infection may occur through ingestion of undercooked meat, such as pork, that is infected with the plerocercoids. In some areas, snakes or tadpoles are consumed raw for medicinal purposes. If they are infected with plerocercoids, these parasites may be capable of penetrating the intestinal wall to infect humans, causing sparganosis. The plerocercoid larva (sparganum) is released in the intestine, then loses the strobila and the scolex and migrates through the intestinal wall to the tissues, where it grows back to its full length.
Human infection may also be caused by the practice of placing poultices of frog or snake flesh on open wounds or other lesions, or the eyes. This practice is common in many Asian cultures.
Hosts & Vectors:
Dogs and cats are the primary hosts of the adult worm. The first intermediate hosts are copepods, or freshwater crustaceans. The second intermediate hosts are amphibians, reptiles, birds, and mammals. Humans are considered to be the accidental intermediate hosts. Snakes and tadpoles/frogs are the vectors for sparganum.
The incubation period is 20 days to 14 months; however, sparganum larva can remain in the body for years or even decades before symptoms present.
The sparganum is a wrinkled, whitish, ribbon-shaped organism, 3 millimeters in width and up to 30 centimeters long. The sparganum is a solid-bodied larva that lacks a bladder, and has bothrids (two longitudinal grooves) at the anterior end, instead of suckers. The larva has an unsegmented strobila 20 to 30 cm in length, bundles of longitudinal muscle fibers scattered throughout the mesenchyme, and a thick tegument.
Copepods, the first intermediate hosts, ingest embryos, or coracidia, that have developed from Spirometra eggs that have been deposited in water sources with the feces of infected hosts. In the tissues of the copepods, the embryos become procercoid (first larva stage). When the second intermediate host ingests the infected copepod, the procercoid migrates through the intestinal wall to the tissues, and develops into the sparganum larva, or plerocercoid. The sparganum develops into the adult Spirometra in the intestines of dogs and cats, which are the primary hosts.
Localization of the lesion by computed tomography (CT) or magnetic resonance imaging (MRI) is helpful in diagnosing sparganosis. Removing the lesion and identifying the tapeworm is often required for definitive diagnosis. In the case of cerebral sparganosis, enzyme-linked immunosorbent assay of cerebrospinal fluid or serum may be diagnostically helpful, but diagnosis is usually made after surgical resection. The following findings on CT scans appear to make a reliable basis for clinical diagnosis of sparganosis affecting the central nervous system: hypodensity, ventricular dilation, irregular or nodular enhancing lesions, and small, punctuate areas of calcification. Experts recommend repeat CT imaging to assess for change in size or location of enhancing nodules, which indicates if the parasite is still alive.
Magnetic Resonance Image showing a round lesion in the subcortical area of the left frontal lobe.
Management and Therapy:
Surgical removal of sparganum larvae is usually curative. Praziquantel may be effective when administered at a total dose of 120 to 150 mg/kg body weight, over a 2-day period. However, treatment with praziquantel has produced only limited success. Cerebral sparganosis requires surgical excision of the parasite; praziquantel has no effect on adult worms in the central nervous system. There is no available treatment for proliferative sparganosis. Attempts at surgical removal of S. proliferum have been unsuccessful because of the widespread dissemination of the larva.
Sparganum that was removed from the right occipital cortex. (http://www.thejns-net.org/jns/issues/v85n6/toc_fs.html)
Epidemiology and Country Information:
Sparganosis is rarely seen in most parts of the world. Most of the human cases of sparganosis come from Asia and North America. Only a few cases have been diagnosed in Europe, Africa, South America, and Australia. S. mansoni predominately afflicts Asia, and S. mansonoides is found in the southeastern United States. S. houghtoni and S. erinacei are found in China and Japan, respectively. Cases of S. proliferum have been reported in Japan, the United States, Venezuela, and Paraguay.
The highest endemicity of sparganosis is in Korea and Japan, mostly because of dietary customs. In Korea, seroprevalence is 8% in some regions, and males are affected ten times more often than females. In a Korean study of sparganosis prevalence, 89% of the patients with cerebral sparganum lived in a rural area, and 75% had a history of ingesting raw frogs or snakes.
Ocular sparganosis is not uncommon in parts of Asia, especially China and Vietnam; cases of cerebral sparganosis have been reported in Korea. Cerebral sparganosis has been reported in Japan, Thailand, Italy, Korea, Greece, Hong Kong, and India.
Most of the cases of sparganosis occur in 20 – 50 year old individuals.
Public Health and Prevention:
In areas of endemic infection, people should be advised of the dangers of drinking water from ponds and ditches, which may contain infected copepods. Basic public health infrastructure should be strengthened so that all people have access to clean drinking water. The use of potentially infected animals for medicinal purposes must be discouraged. Prevention may be difficult because of cultural customs and dietary habits that involve raw frogs and snakes.
The World Health Organization www.who.int
The Centers for Disease Control & Prevention www.cdc.gov
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Parasites & Pestilence: Infectious Public Health Challenges
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