Schistosomiasis

Schistosomiasis, also known as snail fever and bilharzia, is a caused by  s called s. The  or the  may be infected. Symptoms include, , , or. Those who have been infected for a may experience, , , or. In children, it may cause and.

The disease is spread by contact with contaminated with the parasites. These parasites are released from infected s. The disease is especially common among children in developing countries, as they are more likely to play in contaminated water. Other high-risk groups include farmers, fishermen, and people using unclean water during daily living. It belongs to the group of. Diagnosis is by finding eggs of the parasite in a person's urine or stool. It can also be confirmed by finding against the disease in the blood.

Methods to prevent the disease include improving access to clean water and reducing the number of snails. In areas where the disease is common, the medication may be given once a year to the entire group. This is done to decrease the number of people infected, and consequently, the spread of the disease. Praziquantel is also the treatment recommended by the for those who are known to be infected.

Schistosomiasis affected about 252 million people worldwide in 2015. An estimated 4,400 to 200,000 people die from it each year. The disease is most commonly found in Africa, Asia, and South America. Around 700 million people, in more than 70 countries, live in areas where the disease is common. In tropical countries, schistosomiasis is second only to among parasitic diseases with the greatest economic impact. Schistosomiasis is listed as a.

Signs and symptoms
Many individuals do not experience symptoms. If symptoms do appear, they usually take 4–6 weeks from the time of infection. The first symptom of the disease may be a general. Within 12 hours of infection, an individual may complain of a tingling sensation or light, commonly referred to as "", due to irritation at the point of entrance. The rash that may develop can mimic and other types of rashes. Other symptoms can occur 2–10 weeks later and can include, aching, a , , chills, or gland enlargement. These symptoms can also be related to avian schistosomiasis, which does not cause any further symptoms in humans.

The manifestations of schistosomal infection vary over time as the, and later adult worms and their eggs, migrate through the body. If eggs migrate to the brain or spinal cord, seizures, paralysis, or spinal-cord inflammation are possible.

Intestinal schistosomiasis
In intestinal schistosomiasis, eggs become lodged in the intestinal wall and cause an immune system reaction called a. This immune response can lead to obstruction of the colon and blood loss. The infected individual may have what appears to be a potbelly. Eggs can also become lodged in the, leading to high blood pressure through the liver, enlarged , the buildup of fluid in the abdomen, and potentially life-threatening dilations or swollen areas in the esophagus or gastrointestinal tract that can tear and bleed profusely (esophageal varices). In rare instances, the central nervous system is affected. Individuals with chronic active schistosomiasis may not complain of typical symptoms.

Dermatitis
The first potential reaction is an itchy, rash that results from  penetrating the skin, often in a person's first infection. The round bumps are usually one to three centimeters across. Because people living in affected areas have often been repeatedly exposed, acute reactions are more common in tourists and migrants. The rash can occur between the first few hours and a week after exposure and lasts for several days. A similar, more severe reaction called "swimmer's itch" reaction can also be caused by cercariae from animal that often infect birds.

Katayama fever
Another primary condition, called Katayama fever, may also develop from infection with these worms, and it can be very difficult to recognize. Symptoms include fever, lethargy, the eruption of pale temporary bumps associated with severe itching (urticarial) rash, liver and spleen enlargement, and bronchospasm.

Acute schistosomiasis (Katayama fever) may occur weeks or months after the initial infection as a systemic reaction against migrating schistosomulae as they pass through the bloodstream through the lungs to the liver. Similarly to swimmer's itch, Katayama fever is more commonly seen in people with their first infection such as migrants and tourists. It is seen, however, in native residents of China infected with . Symptoms include: The symptoms usually get better on their own, but a small proportion of people have persistent weight loss, diarrhea, diffuse abdominal pain, and rash.
 * Dry cough with changes on
 * Fever
 * Malaise
 * Abdominal pain
 * Enlargement of both the liver and the spleen
 * Abdominal pain
 * Enlargement of both the liver and the spleen

Chronic disease
In long-established disease, adult worms lay eggs that can cause reactions. The eggs secrete s that help them migrate to the bladder and intestines to be shed. The enzymes also cause an inflammatory reaction when eggs get trapped in tissues or embolize to the liver, spleen, s, or. The long-term manifestations are dependent on the species of schistosome, as the adult worms of different species migrate to different areas. Many infections are mildly symptomatic, with and  being common in endemic areas.

Genitourinary disease
The worms of  migrate to the veins around the and s. This can lead to  10 to 12 weeks after infection. Over time, can lead to obstruction of the urinary tract,, and. diagnosis and mortality are generally elevated in affected areas; efforts to control schistosomiasis in have led to decreases in the bladder cancer rate. The risk of bladder cancer appears to be especially high in male smokers, perhaps due to chronic irritation of the bladder lining allowing it to be exposed to s from smoking.

In women, genitourinary disease can also include genital lesions that may lead to increased rates of transmission.

Gastrointestinal disease
The worms of  and S. japonicum migrate to the veins of the gastrointestinal tract and liver. Eggs in the gut wall can lead to pain,, and diarrhea (especially in children). Severe disease can lead to narrowing of the or. Eggs also migrate to the liver leading to fibrosis in 4 to 8% of people with chronic infection, mainly those with long-term heavy infection.

Central nervous system disease
lesions occur occasionally. Cerebral granulomatous disease may be caused by S. japonicum eggs in the brain. Communities in China affected by S. japonicum have rates of eight times higher than baseline. Similarly, granulomatous lesions from S. mansoni and S. haematobium eggs in the can lead to  with flaccid. Eggs are thought to travel to the central nervous system via.

Transmission
Infected individuals release Schistosoma eggs into water via their fecal material or urine. After e hatch from these eggs, the larvae infect a very specific type of freshwater snail. For example, in S. haematobium and S. intercalatum it is snails of the genus ', in S. mansoni it is ', and in S. japonicum it is . The Schistosoma larvae undergo the next phase of their lifecycles in these snails, spending their time reproducing and developing. Once this step has been completed, the parasite leaves the snail and enters the water column. The parasite can live in the water for only 48 hours without a mammalian host. Once a host has been found, the worm enters its blood vessels. For several weeks, the worm remains in the vessels, continuing its development into its adult phase. When maturity is reached, mating occurs and eggs are produced. Eggs enter the bladder/intestine and are excreted through urine and feces and the process repeats. If the eggs do not get excreted, they can become engrained in the body tissues and cause a variety of problems such as immune reactions and organ damage.

Humans encounter larvae of the Schistosoma parasite when they enter contaminated water while bathing, playing, swimming, washing, fishing, or walking through the water.

Identification of eggs in stools
Diagnosis of infection is confirmed by the identification of eggs in stools. Eggs of S. mansoni are about 140 by 60 µm in size and have a lateral spine. The diagnosis is improved through the use of the, a semiquantitative stool examination technique. Other methods that can be used are, circumoval precipitation test, and alkaline phosphatase immunoassay.

Microscopic identification of eggs in or urine is the most practical method for diagnosis. 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). Because eggs may be passed intermittently or in small numbers, their detection is enhanced by repeated examinations or concentration procedures, or both. In addition, for field surveys and investigational purposes, the egg output can be quantified by using the Kato-Katz technique (20 to 50 mg of fecal material) or the. Eggs can be found in the urine in infections with S. haematobium (recommended time for collection: between noon and 3 PM) and with S. japonicum. Quantification is possible by using filtration through a membrane of a standard volume of urine followed by egg counts on the membrane. 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.

Antibody detection
Antibody detection can be useful to indicate schistosome infection in people who have traveled to areas where schistosomiasis is common and in whom eggs cannot be demonstrated in fecal or urine specimens. Test sensitivity and specificity vary widely among the many tests reported for the serologic diagnosis of schistosomiasis and are dependent on both the type of antigen preparations used (crude, purified, adult worm, egg, cercarial) and the test procedure.

At the U.S., a combination of tests with purified adult worm antigens is used for antibody detection. All serum specimens are tested by FAST-ELISA using S. mansoni adult microsomal antigen. A positive reaction (greater than 9 units/µl serum) indicates infection with Schistosoma species. Sensitivity for S. mansoni infection is 99%, 95% for S. haematobium infection, and less than 50% for S. japonicum infection. Specificity of this assay for detecting schistosome infection is 99%. Because test sensitivity with the FAST-ELISA is reduced for species other than S. mansoni, immunoblots of the species appropriate to the patient's travel history are also tested to ensure detection of S. haematobium and S. japonicum infections. Immunoblots with adult worm microsomal antigens are species-specific, so a positive reaction indicates the infecting species. The presence of antibody is indicative only of schistosome infection at some time and cannot be correlated with clinical status, worm burden, egg production, or prognosis. Where a person has traveled can help determine which Schistosoma species to test for by immunoblot.

In 2005, a field evaluation of a novel handheld microscope was undertaken in 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.

Prevention
Many countries are working towards eradicating the disease. The is promoting these efforts. In some cases, urbanization, pollution, and the consequent destruction of snail habitat have reduced exposure, with a subsequent decrease in new infections. The drug praziquantel is used for prevention in high-risk populations living in areas where the disease is common. The advises avoiding drinking or coming into contact with contaminated water in areas where schistosomiasis is common.

A 2014 review found tentative evidence that increasing access to and  reduces schistosome infection.

Snails, dams, and prawns
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 United Nations 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. Even though guidelines on how to design these schemes to minimise the spread of the disease had been published years before, the designers were unaware of them. The dams appear to have reduced the population of the large migratory prawn . After the construction of fourteen large dams, greater increases in schistosomiasis occurred in the historical habitats of native prawns than in other areas. Further, at the 1986 on the, restoring prawns upstream of the dam reduced both snail density and the human schistosomiasis reinfection rate.

Integrated strategy in China
In, the national strategy for schistosomiasis japonica control has shifted three times since it was first initiated: transmission control strategy (from mid-1950s to early 1980s), morbidity control strategy (from mid-1980s to 2003), and the "new integrated strategy" (2004 to present). The morbidity control strategy focused on synchronous chemotherapy for humans and bovines and the new strategy developed in 2004 intervenes in the transmission pathway of schistosomiasis, mainly including replacement of bovines with machines, prohibition of grazing cattle in the grasslands, improving sanitation, installation of fecal-matter containers on boats, drug therapy, snail control, and health education. A 2018 review found that the "new integrated strategy" was highly effective to reducing the rate of S. japonicum infection in both humans and the intermediate host snails and reduced the infection risk by 3–4 times relative to the conventional strategy.

Treatment
Two drugs, and, are available for the treatment of schistosomiasis. They are considered equivalent in relation to efficacy against S. mansoni and safety. Because of praziquantel's lower cost per treatment, and oxaminiquine's lack of efficacy against the urogenital form of the disease caused by S. haematobium, in general praziquantel is considered the first option for treatment. The treatment objective is to cure the disease and to prevent the evolution of the acute to the chronic form of the disease. All cases of suspected schistosomiasis should be treated regardless of presentation because the adult parasite can live in the host for years.

Schistosomiasis is treatable by taking by mouth a single dose of the drug praziquantel annually.

The WHO has developed guidelines for community treatment based on the impact the disease has on children in villages in which it is common:
 * When a village reports more than 50 percent of children have blood in their urine, everyone in the village receives treatment.
 * When 20 to 50 percent of children have bloody urine, only school-age children are treated.
 * When fewer than 20 percent of children have symptoms, mass treatment is not implemented.

Other possible treatments include a combination of praziquantel with, , or. A Cochrane review found tentative evidence that when used alone, metrifonate was as effective as praziquantel.

Another agent, mefloquine, which has previously been used to treat and prevent malaria, was recognised in 2008–2009 to be effective against Schistosoma.

Historically, remained the treatment of choice for schistosomiasis until the development of praziquantel in the 1980s.

Epidemiology
The disease is found in countries in Africa, the, eastern South America, , and the. S. 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. S. mekongi and S. intercalatum are found locally in and central, respectively.

The disease is in about 75 developing countries and mainly affects people living in rural agricultural and peri-urban areas.

Infection estimates
In 2010, approximately 238 million people were infected with schistosomiasis, 85 percent of whom live in Africa. An earlier estimate from 2006 had put the figure at 200 million people infected. In many of the affected areas, schistosomiasis infects a large proportion of children under 14 years of age. An estimated 600 to 700 million people worldwide are at risk from the disease because they live in countries where the organism is common. In 2012, 249 million people were in need of treatment to prevent the disease. This likely makes it the most common parasitic infection with malaria second and causing about 207 million cases in 2013.

S. haematobium, the infectious agent responsible for urogenital schistosomiasis, infects over 112 million people annually in Sub-Saharan Africa alone. It is responsible for 32 million cases of, 10 million cases of , and 150,000 deaths from annually, making S. haematobium the world’s deadliest schistosome.

Deaths
Estimates regarding the number of deaths vary. Worldwide, the issued in 2010 estimated 12,000 direct deaths while the WHO in 2014 estimated more than 200,000 annual deaths related to schistosomiasis. Another 20 million have severe consequences from the disease. It is the most deadly of the neglected tropical diseases.

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

The first physician who described the entire disease cycle was the Brazilian parasitologist in 1908. The earliest known case of infection was discovered in 2014, belonging to a child who lived 6,200 years ago.

It was a common cause of death for.

In 2016 more than 200 million people needed treatment but only 88 million people were actually treated for schistosomiasis.

Etymology
Schistosomiasis is named for the genus of parasitic flatworm Schistosoma, whose name means 'split body'. The name Bilharzia comes from, a  working in  in 1851 who first discovered these worms.

Society and culture
Schistosomiasis is endemic in Egypt, exacerbated by the country's dam and irrigation projects along the. From the late 1950s through the early 1980s, infected villagers were treated with repeated injections of. Epidemiological evidence suggests that this campaign unintentionally contributed to the spread of 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. From ancient times to the early 20th century, schistosomiasis' symptom of blood in the urine was seen as a in Egypt and was thus viewed as a  for boys.

Among human parasitic diseases, schistosomiasis ranks second behind malaria in terms of socio-economic and public health importance in tropical and subtropical areas.

Research
As of September 2014, a vaccine called "Bilhvax" against S. haematobium infection is being developed. As of September 2016, no results from the Phase III clinical trials completed in 2012 have been reported.

Using, researchers decreased the symptoms due to schistosomiasis in an animal model.