Schistosomiasis

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Schistosomiasis
Classification and external resources
Schistosomiasis itch.jpeg
Skin blisters on the forearm, created by the entrance of Schistosoma parasite.
ICD-10 B65
ICD-9 120
MedlinePlus 001321
MeSH D012552

Schistosomiasis /ˌʃistəsɵˈməsəs/ (also known as bilharzia, snail fever, and Katayama fever)[1][2] is a disease caused by parasitic worms of the Schistosoma type. It may infect the urinary tract or intestines. Symptoms may include abdominal pain, diarrhea, bloody stool, or blood in the urine. In those who have been infected a long time, liver damage, kidney failure, infertility, or bladder cancer may occur. In children it may cause poor growth and learning difficulty.[3]

The disease is spread by contact with water that contains the parasites. These parasites are released from freshwater snails that have been infected. The disease is especially common among children in developing countries as they are more likely to play in infected water. Other high risk groups include farmers, fishermen, and people using infected water for their daily chores. Diagnosis is by finding the eggs of the parasite in a person's urine or stool. It can also be confirmed by finding antibodies against the disease in the blood.[3]

Methods to prevent the disease include improving access to clean water and reducing the number of snails. In areas where the disease is common entire groups may be treated all at once and yearly with the medication praziquantel. This is done to decrease the number of people infected and therefore decrease the spread of the disease. Praziquantel is also the treatment recommended by the World Health Organization for those who are known to be infected.[3]

Schistosomiasis affects almost 210 million people worldwide,[4] and an estimated 12,000[5] to 200,000 people die from it a year.[6] The disease is most commonly found in Africa, Asia and South America.[3] Around 700 million people, in more than 70 countries, live in areas where the disease is common.[6][7] Schistosomiasis is second only to malaria, as a parasitic disease with the greatest economic impact.[8]

Classification[edit]

Species of Schistosoma that can infect humans:

Avian schistosomiasis species cause swimmer's itch and clam digger itch

Species of Schistosoma that can infect other animals:

S. bovis — normally infects cattle, sheep and goats in Africa, parts of Southern Europe and the Middle East
S. mattheei — normally infects cattle, sheep and goats in Central and Southern Africa
S. margrebowiei — normally infects antelope, buffalo and waterbuck in Southern and Central Africa
S. curassoni — normally infects domestic ruminants in West Africa
S. rodhaini — normally infects rodents and carnivores in parts of Central Africa

Signs and symptoms[edit]

Above all, schistosomiasis is a chronic disease. Many infections are subclinically symptomatic, with mild anemia and malnutrition being common in endemic areas. Acute schistosomiasis (Katayama's fever) may occur weeks after the initial infection, especially by S. mansoni and S. japonicum. Manifestations include:

Occasionally central nervous system lesions occur: cerebral granulomatous disease may be caused by ectopic S. japonicum eggs in the brain, and granulomatous lesions around ectopic eggs in the spinal cord from S. mansoni and S. haematobium infections may result in a transverse myelitis with flaccid paraplegia.[13]

Calcification of the bladder wall on a plain x-ray image of the pelvis, in a 44 year old sub-Saharan man. This is due to urinary schistosomiasis.

Continuing infection may cause granulomatous reactions and fibrosis in the affected organs, which may result in manifestations that include:

Bladder cancer diagnosis and mortality are generally elevated in affected areas.

Pathophysiology[edit]

Life cycle[edit]

Schistosoma life cycle. Source: CDC

Schistosomes have a typical trematode vertebrate-invertebrate lifecycle, with humans being the definitive host.

Snails[edit]

The life cycles of all five human schistosomes are broadly similar: parasite eggs are released into the environment from infected individuals, hatching on contact with fresh water to release the free-swimming miracidium. Miracidia infect freshwater snails by penetrating the snail's foot. After infection, close to the site of penetration, the miracidium transforms into a primary (mother) sporocyst. Germ cells within the primary sporocyst will then begin dividing to produce secondary (daughter) sporocysts, which migrate to the snail's hepatopancreas. Once at the hepatopancreas, germ cells within the secondary sporocyst begin to divide again, this time producing thousands of new parasites, known as cercariae, which are the larvae capable of infecting mammals.

Cercariae emerge daily from the snail host in a circadian rhythm, dependent on ambient temperature and light. Young cercariae are highly mobile, alternating between vigorous upward movement and sinking to maintain their position in the water. Cercarial activity is particularly stimulated by water turbulence, by shadows and by chemicals found on human skin.

The most common way of getting schistosomiasis in developing countries is by wading or swimming in lakes, ponds and other bodies of water that are infested with the snails (usually of the genera Biomphalaria, Bulinus, or Oncomelania) that are the natural reservoirs of the Schistosoma pathogen.

Humans[edit]

Penetration of the human skin occurs after the cercaria have attached to and explored the skin. The parasite secretes enzymes that break down the skin's protein to enable penetration of the cercarial head through the skin. As the cercaria penetrates the skin it transforms into a migrating schistosomulum stage.

Photomicrography of bladder in S. hematobium infection, showing clusters of the parasite eggs with intense eosinophilia, Source: CDC

The newly transformed schistosomulum may remain in the skin for two days before locating a post-capillary venule; from here the schistosomulum travels to the lungs where it undergoes further developmental changes necessary for subsequent migration to the liver. Eight to ten days after penetration of the skin, the parasite migrates to the liver sinusoids. S. japonicum migrates more quickly than S. mansoni, and usually reaches the liver within eight days of penetration. Juvenile S. mansoni and S. japonicum worms develop an oral sucker after arriving at the liver, and it is during this period that the parasite begins to feed on red blood cells. The nearly-mature worms pair, with the longer female worm residing in the gynaecophoric channel of the shorter male. Adult worms are about 10 mm long. Worm pairs of S. mansoni and S. japonicum relocate to the mesenteric or rectal veins. S. haematobium schistosomula ultimately migrate from the liver to the perivesical venous plexus of the bladder, ureters, and kidneys through the hemorrhoidal plexus.

Parasites reach maturity in six to eight weeks, at which time they begin to produce eggs. Adult S. mansoni pairs residing in the mesenteric vessels may produce up to 300 eggs per day during their reproductive lives. S. japonicum may produce up to 3,000 eggs per day. Many of the eggs pass through the walls of the blood vessels, and through the intestinal wall, to be passed out of the body in feces. S. haematobium eggs pass through the ureteral or bladder wall and into the urine. Only mature eggs are capable of crossing into the digestive tract, possibly through the release of proteolytic enzymes, but also as a function of host immune response, which fosters local tissue ulceration. Up to half the eggs released by the worm pairs become trapped in the mesenteric veins, or will be washed back into the liver, where they will become lodged. Worm pairs can live in the body for an average of four and a half years, but may persist up to twenty years.

Trapped eggs mature normally, secreting antigens that elicit a vigorous immune response. The eggs themselves do not damage the body. Rather it is the cellular infiltration resultant from the immune response that causes the pathology classically associated with schistosomiasis.

Diagnosis[edit]

High powered detailed micrograph of Schistosoma parasite eggs in human bladder tissue.
S. japonicum eggs in hepatic portal tract.

Contemporary diagnosis involves detection of parasitic antigens by ELISA; all that is required from the patient is a blood sample. This screening method is highly effective. Microscopic identification of eggs in stool or, less commonly, the urine is another way of arriving at a positive diagnosis. For the measurement of eggs in the feces of presenting patients the scientific unit used is eggs per gram (epg). Stool examination should be performed when infection with S. mansoni or S. japonicum is suspected, and urine examination should be performed if S. haematobium is suspected.

Eggs can be present in the stool in infections with all Schistosoma species. The examination can be performed on a simple smear (1 to 2 mg of fecal material). Since eggs may be passed intermittently or in small amounts, their detection will be enhanced by repeated examinations and/or concentration procedures (such as the formalin-ethyl acetate technique). In addition, for field surveys and investigational purposes, the egg output can be quantified by using the Kato technique (20 to 50 mg of fecal material) or the Ritchie technique.

Eggs can be found in the urine in infections with S. japonicum and with S. intercalatum (recommended time for collection: between noon and 3 p.m.) Detection will be enhanced by centrifugation and examination of the sediment. Quantification is possible by using filtration through a nucleopore membrane of a standard volume of urine followed by egg counts on the membrane. Investigation of S. haematobium should also include a pelvic x-ray as bladder wall calcification is highly characteristic of chronic infection.

Recently a field evaluation of a novel handheld microscope was undertaken in Uganda for the diagnosis of intestinal schistosomiasis by a team led by Russell Stothard from the Natural History Museum of London, working with the Schistosomiasis Control Initiative, London.[14]

Tissue biopsy (rectal biopsy for all species and biopsy of the bladder for S. haematobium) may demonstrate eggs when stool or urine examinations are negative.

The eggs of S. haematobium are ellipsoidal with a terminal spine, S. mansoni eggs are also ellipsoidal but with a lateral spine, S. japonicum eggs are spheroidal with a small knob.

Antibody detection can be useful in both clinical management and for epidemiologic surveys.

Prevention[edit]

A few countries have eradicated the disease, and many more are working toward it.[citation needed] The World Health Organization is promoting these efforts. In some cases, urbanization, pollution, and/or consequent destruction of snail habitat has reduced exposure, with a subsequent decrease in new infections.

Snails[edit]

Prevention is best accomplished by eliminating the water-dwelling snails that are the natural reservoir of the disease. Acrolein, copper sulfate, and niclosamide can be used for this purpose. Recent studies have suggested that snail populations can be controlled by the introduction of, or augmentation of existing, crayfish populations.

For many years from the 1950s onwards, vast dams and irrigation schemes were constructed, causing a massive rise in water-borne infections from schistosomiasis. The detailed specifications laid out in various UN documents since the 1950s could have minimized this problem. Irrigation schemes can be designed to make it hard for the snails to colonize the water, and to reduce the contact with the local population.[15]

This has been cited as a classic case of the relevance paradox because guidelines on how to design these schemes to minimise the spread of the disease had been published years before, but the designers were unaware of them.[16]

Treatment[edit]

Main article: Schistosomicide
Ethiopian children treated for schistosoma mansoni

Schistosomiasis is readily treated using a single oral dose of the drug praziquantel annually.[17] As with other major parasitic diseases, there is ongoing and extensive research into developing a schistosomiasis vaccine that will prevent the parasite from completing its life cycle in humans. In 2009, Eurogentec Biologics developed a vaccine against bilharziosis in partnership with INSERM and researchers from the Pasteur Institute.[18][19][20]

The World Health Organization has developed guidelines for community treatment of schistosomiasis based on the impact the disease has on children in endemic villages:[17]

  • When a village reports more than 50 percent of children have blood in their urine, everyone in the village receives treatment.[17]
  • When 20 to 50 percent of children have bloody urine, only school-age children are treated.[17]
  • When fewer than 20 percent of children have symptoms, mass treatment is not implemented.[17]

The Bill & Melinda Gates Foundation has recently funded an operational research program — the Schistosomiasis Consortium for Operational Research and Evaluation (SCORE) to answer strategic questions about how to move forward with schistosomiasis control and elimination. The focus of SCORE is on development of tools and evaluation of strategies for use in mass drug administration campaigns.

Antimony has been used in the past to treat the disease. In low doses, this toxic metalloid bonds to sulfur atoms in enzymes used by the parasite and kills it without harming the host. This treatment is not referred to in present-day peer review scholarship; praziquantel is universally used. Outside of the U.S., there is a drug available exclusively for treating Schistosoma mansoni (oxamniquine) and one exclusively for treating S. hematobium (metrifonate). While metrifonate has been discontinued for use by the British National Health Service, a Cochrane review found it equally effective in treating urinary schistosomiasis as the leading drug, praziquantel.[21]

Mirazid, an Egyptian drug made from myrrh, was under investigation for oral treatment of the disease up until 2005.[22] The efficacy of praziquantel was proven to be about eight times than that of Mirazid and therefore Mirazid was not recommended as a suitable agent to control schistosomiasis.[23]

Another agent, mefloquine, which has previously been used to treat malaria, was recognised in 2008-2009 to be effective against schistosoma.[24] Mefloquine may be used in combination with praziquantel or artemisinins. Its mechanism of action is not known but it causes extensive and severe morphological, histopathological, and ultrastructural damage to adult and juvenile schistosomes, particularly, the worm tegument, musculature, gut, and vitelline glands of female worms.

Epidemiology[edit]

Disability-adjusted life year for schistosomiasis per 100,000 inhabitants.
  no data
  less than 50
  50-75
  75-100
  100-150
  150-200
  200-250
  250-300
  300-350
  350-400
  400-450
  450-500
  more than 500

The disease is found in tropical countries in Africa, the Caribbean, eastern South America, Southeast Asia and in the Middle East. In these areas as of 2010 it affects approximately 238 million people[25] 85% of whom live in Africa. An estimated 600 million people worldwide are at risk from the disease.[6]

Worldwide an estimated 12,000[5] to 200,000 people die related to schistosomiasis yearly.[6]

Schistosoma mansoni is found in parts of South America and the Caribbean, Africa, and the Middle East; S. haematobium in Africa and the Middle East; and S. japonicum in the Far East. S. mekongi and S. intercalatum are found locally in Southeast Asia and central West Africa, respectively.

Among human parasitic diseases, schistosomiasis (sometimes called bilharziasis) ranks second behind malaria in terms of socio-economic and public health importance in tropical and subtropical areas. The disease is endemic in 74-76 developing countries. They live in rural agricultural and peri-urban areas.[26]

20 million have severe consequences from the disease.[27] In many areas, schistosomiasis infects a large proportion of children under 14 years of age.

History[edit]

Schistosomiasis is known as bilharzia or bilharziosis in many countries, after German physician Theodor Bilharz, who first described the cause of urinary schistosomiasis in 1851.

The first doctor who described the entire disease cycle was Brazilian parasitologist Pirajá da Silva in 1908. The first known case of infection was discovered in 2014, it belongs to a child who lived 6,200 years ago.[28]

It was a common cause of death for Ancient Egyptians in the Greco-Roman Period.[29]

Society and culture[edit]

Schistosomiasis is endemic in Egypt, exacerbated by the country's dam and irrigation projects along the Nile. From the late 1950s through the early 1980s, infected villagers were treated with repeated injections of tartar emetic. Epidemiological evidence suggests that this campaign unintentionally contributed to the spread of hepatitis C via unclean needles. Egypt has the world's highest hepatitis C infection rate, and the infection rates in various regions of the country closely track the timing and intensity of the anti-schistosomiasis campaign.[30]

See also[edit]

References[edit]

  1. ^ "Schistosomiasis (bilharzia)". NHS Choices. Dec 17, 2011. Retrieved 15 March 2014. 
  2. ^ "Schistosomiasis". Patient.co.uk. 12/02/2013. Retrieved 11 June 2014. 
  3. ^ a b c d "Schistosomiasis Fact sheet N°115". World Health Organization. February 2014. Retrieved 15 March 2014. 
  4. ^ Fenwick, A (Mar 2012). "The global burden of neglected tropical diseases.". Public health 126 (3): 233–6. PMID 22325616. 
  5. ^ a b Lozano, R; Naghavi, M; Foreman, K; Lim, S; Shibuya, K; Aboyans, V; Abraham, J; Adair, T et al. (Dec 15, 2012). "Global and regional mortality from 235 causes of death for 20 age groups in 1990 and 2010: a systematic analysis for the Global Burden of Disease Study 2010". Lancet 380 (9859): 2095–128. doi:10.1016/S0140-6736(12)61728-0. PMID 23245604. 
  6. ^ a b c d Thétiot-Laurent, SA; Boissier, J; Robert, A; Meunier, B (Jun 27, 2013). "Schistosomiasis Chemotherapy". Angewandte Chemie (International ed. in English) 52 (31): 7936–56. doi:10.1002/anie.201208390. PMID 23813602. 
  7. ^ "Schistosomiasis A major public health problem". World Health Organization. Retrieved 15 March 2014. 
  8. ^ The Carter Center. "Schistosomiasis Control Program". Retrieved 2008-07-17. 
  9. ^ p.771 Robbin and Cotran Pathological Basis of Disease 8th
  10. ^ Donald G. McNeil, Jr. (May 25, 2009). "Parasites: Giving a Deworming Drug to Girls Could Cut H.I.V. Transmission in Africa". The New York Times. 
  11. ^ Hotez PJ, Fenwick A, Kjetland EF (2009). "Africa's 32 Cents Solution for HIV/AIDS". PLoS Negl Trop Dis 3 (5): e430. doi:10.1371/journal.pntd.0000430. PMC 2682705. PMID 19479041. 
  12. ^ James, William D.; Berger, Timothy G.; et al. (2006). Andrews' Diseases of the Skin: clinical Dermatology. Saunders Elsevier. ISBN 0-7216-2921-0. 
  13. ^ FREITAS, André Ricardo Ribas; OLIVEIRA, Augusto César Penalva and SILVA, Luiz Jacintho. Schistosomal myeloradiculopathy in a low-prevalence area: 27 cases (14 autochthonous) in Campinas, São Paulo, Brazil. Mem. Inst. Oswaldo Cruz [online]. 2010, vol.105, n.4, pp. 398-408. ISSN 0074-0276 http://www.scielo.br/pdf/mioc/v105n4/09.pdf
  14. ^ Stothard, J. Russell; et al. (2005). "Field Evaluation of the Meade Readview Handheld Microscope for Diagnosis of Intestinal Schistosomiasis in Ugandan School Children". Am. J. Trop. Med. Hyg. (American Society of Tropical Medicine and Hygiene) 73 (5): 949–955. PMID 16282310. 
  15. ^ Charnock, Anne (7 August 1980). "Taking Bilharziasis out of the irrigation equation". New Civil Engineer. "Bilharzia caused by poor civil engineering design due to ignorance of cause and prevention" 
  16. ^ The IRG Solution — hierarchical incompetence and how to overcome it. London: Souvenir Press. 1984. p. 88. 
  17. ^ a b c d e The Carter Center. "How is Schistosomiasis Treated?". Archived from the original on 2008-02-25. Retrieved 2008-07-17. 
  18. ^ "BILHVAX — A VACCINE AGAINST BILHARZIOSE, A world first!". 20 April 2009. 
  19. ^ "300.000 morts évitées grâce au vaccin liégeois!". 20 April 2009. 
  20. ^ "Eurogentec, la société de biotechnologie située au Sart Tilman, produit et produira le vaccin contre la bilharziose.". 22 April 2009. 
  21. ^ Danso-Appiah A, Utzinger J, Liu J, Olliaro P (2008). "Drugs for treating urinary schistosomiasis". In Danso-Appiah, Anthony. Cochrane Database Syst Rev (3): CD000053. doi:10.1002/14651858.CD000053.pub2. 
  22. ^ See, for example, Soliman OE, et al.; El-Arman, M; Abdul-Samie, ER; El-Nemr, HI; Massoud, A (December 2004). "Evaluation of myrrh (Mirazid) therapy in fascioliasis and intestinal schistosomiasis in children: immunological and parasitological study". J Egypt Soc Parasitol 34 (3): 941–66. PMID 15587320. 
  23. ^ Botros, S; Sayed, H; El-Dusoki, H; Sabry, H; Rabie, I; El-Ghannam, M; Hassanein, M; El-Wahab, YA; Engels, D (February 2005). "Efficacy of mirazid in comparison with praziquantel in Egyptian Schistosoma mansoni-infected school children and households". Am J Trop Med Hyg 72 (2): 119–23. PMID 15741544. 
  24. ^ Xiao SH (2013) Mefloquine, a new type of compound against schistosomes and other helminthes in experimental studies. Parasitol Res
  25. ^ Vos, T; Flaxman, AD; Naghavi, M; Lozano, R; Michaud, C; Ezzati, M; Shibuya, K; Salomon, JA et al. (Dec 15, 2012). "Years lived with disability (YLDs) for 1160 sequelae of 289 diseases and injuries 1990-2010: a systematic analysis for the Global Burden of Disease Study 2010". Lancet 380 (9859): 2163–96. doi:10.1016/S0140-6736(12)61729-2. PMID 23245607. 
  26. ^ Oliveira, G.; Rodrigues N.B., Romanha, A.J., Bahia, D. (2004). "Genome and Genomics of Schistosomes". Canadian Journal of Zoology 82 (2): 375–90. doi:10.1139/Z03-220. 
  27. ^ Kheir MM, Eltoum IA, Saad AM, Ali MM, Baraka OZ, Homeida MM (February 1999). "Mortality due to schistosomiasis mansoni: a field study in Sudan". Am. J. Trop. Med. Hyg. 60 (2): 307–10. PMID 10072156. 
  28. ^ http://news.nationalpost.com/2014/06/20/ancient-parasite-egg-found-in-6200-year-old-child-skeleton-gives-earliest-evidence-of-a-modern-disease/.  Missing or empty |title= (help)
  29. ^ "Proceedings of the 13h Annual History of Medicine Days", a medical historical paper from University of Calgary. March 2004.
  30. ^ Strickland GT (May 2006). "Liver disease in Egypt: hepatitis C superseded schistosomiasis as a result of iatrogenic and biological factors". Hepatology 43 (5): 915–22. doi:10.1002/hep.21173. PMID 16628669. 

Further reading[edit]

External links[edit]