Neuroschistosomiasis

Ernest Nwazor FMCP MBBS (Dr. Nwazor of University of Port Harcourt Teaching Hospital (UPTH) has no relevant financial relationships to disclose.)
Kiran Thakur MD (Dr. Thakur of Johns Hopkins Hospital has no relevant financial relationships to disclose.)
Joseph R Zunt MD MPH (Dr. Zunt of the University of Washington has no relevant financial relationships to disclose.)
Karen L Roos MD FAAN, editor. (Dr. Roos of Indiana University School of Medicine has no relevant financial relationships to disclose.)
Originally released February 8, 2015; expires February 8, 2018

Overview

Schistosomiasis, a helmintic infection caused by a blood fluke of the genus Schistosoma, remains one of the most widespread parasitic infections in the world (Carod-Artal 2008; Clerinx and Van Gompel 2011). Despite advances in diagnosis and treatment, schistosomiasis continues to cause significant disability in endemic regions.

Neuroschistosomiasis refers to infection of the central nervous system caused by Schistosoma species, most commonly Schistosoma japonicum, Schistosoma mansoni, and Schistosoma hematobium. Spinal cord disease is the most commonly reported manifestation of both Schistosoma mansoni and Schistosoma japonicum infection whereas involvement of the brain is typical of Schistosoma japonicum infection (Carod-Artal 2008). Neuroschistosomiasis is likely underdiagnosed and may provoke greater disability than the systemic infection.

Key points

 

• Schistosomiasis is a common intravascular infection caused by parasitic Schistosoma trematode worms.

 

• People are infected during routine agricultural, domestic, occupational, and recreational activities that expose them to infested water.

 

• Involvement of the central nervous system by schistosomes may or may not determine clinical manifestations.

 

• Neuroschistosomiasis results from migration of parasite eggs into the nervous tissue and resultant host immune response.

 

• Antischistosomal drugs, corticosteroids, and surgery are useful for treating neuroschistosomiasis.

Historical note and terminology

In 1851, Theodor Bilharz Maximilian, a German Surgeon, discovered the trematode worm in an autopsy while working at the Kasr-el-Aini Hospital of Cairo in Egypt, initially naming it Distomum haematobium. Later in 1851, he communicated his findings to his old teacher, Carl Theodor Ernst von Siebold in a series of letters. In 1853, extracts from these letters together with von Siebold's comments were published in the German Zoological Journal (Bilharz and von Siebold 1853).

Due to the peculiar morphology of the worm, it was clear that it could not be included in the genus Distomum as was initially proposed; thus, the parasite was described in 1856 as Bilharzia haematobium by Meckel Von Hemsbach in a thesis entitled “The Geology of the Human Body” (Meckel 1856). Weinland, apparently not knowing of this thesis, re-described the worm as Schistosoma haematobium in 1958 (Weinland 1858). However, in 1948, the International Commission on Zoological Nomenclature established the name Schistosoma and it is, thus, the current name of the parasite (International Commission on Zoological Nomenclature 1950). Bilharz also described Schistosoma mansoni, but this species was re-described by Louis Westenra Sambon in 1907 at the London School of Tropical Medicine who named it after his teacher Patrick Manson (Brant et al 2006). The life cycle was described by da Silva in 1908 (Brant et al 2006).

Molecular phylogenetic studies suggest that Schistosoma spp. originated in Asia and that a pulmonate-transmitted progenitor colonized Africa and gave rise to both the terminal-spined and lateral-spined egg species groups, the latter containing Schistosoma mansoni (Sambon 1907).

Schistosoma mansoni likely appeared only after the transatlantic dispersal of Biomphalaria from the neotropica to Africa, an event based on African fossil record, occurred about 2 to 5 million years ago. This parasite became abundant in tropical Africa and then entered the New World with the slave trade (Morgan et al 2003).

Schistosomiasis was originally thought to have been exported from Africa to South America during the period of slave trade where it found favorable climatic conditions that promoted its spread. Factors that favor spread include growth in international travel, refugee and population migration, and the development of new water resources (Ross at el 2002). Schistosomiasis is more common among travelers returning from the tropics.

Five species of Schistosoma are known to infect humans: Schistosoma mansoni, Schistosoma hematobium, and Schistosoma japonicum are the most widely distributed whereas Schistosoma mekongi and Schistosoma intercalatum are restricted in geographic distribution. Most granulomas following schistosomal infection develop in the intestine, the liver (Schistosoma mansoni and Schistosoma japonicum), or the genitourinary tract (Schistosoma haematobium) (Ross et al 2002). Cerebral schistosomiasis is usually caused by Schistosoma japonicum whereas Schistosoma mansoni and Schistosoma haematobium typically cause myelopathy (Pollner 1994).

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