General Characteristics and Epidemiology

General features of Schistosoma

• Trematode 
• Parasitic flatworm
• Eggs:
  • Round or oval shaped
  • Hinged at 1 end
• Adults:
  • Elongated
  • Tubular
  • 10–20 mm long
  • Males are shorter than females.
  • Oral and ventral suckers

Clinically relevant species

• GI disease:
  • S. mansoni
  • S. japonicum
  • S. mekongi
  • S. intercalatum
• Genitourinary tract disease: S. haematobium

Epidemiology

• Worldwide annual incidence: 200–300 million
• Men > women
• Children and adolescents > adults
• Mortality rate: 0.3 per 100,000 cases

Geographic distribution

• S. mansoni:
  • Sub-Saharan Africa
  • South America
  • Caribbean
  • Middle East
• S. japonicum:
  • China
  • Philippines
  • Thailand
  • Indonesia
• S. haematobium:
  • Africa
  • Middle East
• S. mekongi: Southeast Asia
• S. intercalatum: Central and West Africa

Pathogenesis

Reservoir

• Humans
• Mammals:
  • Domesticated and wild animals
  • Livestock
• Freshwater snails are intermediate hosts.

Transmission

Transmission occurs through skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin contact with infected fresh water.

Host risk factors

Schistosoma occupies freshwater environments in areas with poor sewerage management.

• Recreational exposures:  
  • Swimming
  • Playing in water or mud
• Occupational exposures: 
  • Fishing
  • Laundry

Life cycle

• Schistosoma larvae (miracidia) penetrate a snail (intermediate host) → asexual reproduction and maturation into cercariae → released from the snail into water
• Cercariae penetrate human skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin → become schistosomulae after shedding their forked tails
• Migration into the bloodstream → infect the liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver → maturation and reproduction
• Adult worms move through the portal vessels to the mesenteric venules of the intestines.
• The females lay eggs → penetrate the intestines → excreted in feces
• Eggs hatch in water → cycle continues
• Note: S. haematobium occupy the vesical venous plexus → eggs are excreted in the urine

Pathophysiology

Clinical disease is caused by:

• Movement of eggs through the splanchnic venous system to:
  • Liver
  • Lungs Lungs Lungs are the main organs of the respiratory system. Lungs are paired viscera located in the thoracic cavity and are composed of spongy tissue. The primary function of the lungs is to oxygenate blood and eliminate CO2. Lungs
  • Spleen Spleen The spleen is the largest lymphoid organ in the body, located in the LUQ of the abdomen, superior to the left kidney and posterior to the stomach at the level of the 9th-11th ribs just below the diaphragm. The spleen is highly vascular and acts as an important blood filter, cleansing the blood of pathogens and damaged erythrocytes. Spleen
  • Brain
  • Spinal cord Spinal cord The spinal cord is the major conduction pathway connecting the brain to the body; it is part of the CNS. In cross section, the spinal cord is divided into an H-shaped area of gray matter (consisting of synapsing neuronal cell bodies) and a surrounding area of white matter (consisting of ascending and descending tracts of myelinated axons). Spinal Cord
• Immune response to proteins and carbohydrates Carbohydrates Carbohydrates are one of the 3 macronutrients, along with fats and proteins, serving as a source of energy to the body. These biomolecules store energy in the form of glycogen and starch, and play a role in defining the cellular structure (e.g., cellulose). Basics of Carbohydrates secreted by the eggs leads to:
  • Bowel inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation → blood loss and scarring
  • Periportal fibrosis → portal hypertension Portal hypertension Portal hypertension is increased pressure in the portal venous system. This increased pressure can lead to splanchnic vasodilation, collateral blood flow through portosystemic anastomoses, and increased hydrostatic pressure. There are a number of etiologies, including cirrhosis, right-sided congestive heart failure, schistosomiasis, portal vein thrombosis, hepatitis, and Budd-Chiari syndrome. Portal Hypertension and esophageal varices
  • Bladder inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation → pseudopolyps and bladder cancer

Clinical Presentation

Most patients are asymptomatic. Symptomatic individuals can present in several ways:

Acute schistosome dermatitis

Also known as “swimmer’s itch”:

• Pruritic rash at the site of cercariae entry:
  • May be papular or urticarial
  • Due to a hypersensitivity reaction
• Feet and lower legs are more often affected.

Acute schistosomiasis syndrome (Katayama fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever)

Occurs due to a systemic hypersensitivity reaction 3–8 weeks after the initial infection:

• Fever
• Chills
• Fatigue
• Urticaria Urticaria Urticaria is raised, well-circumscribed areas (wheals) of edema (swelling) and erythema (redness) involving the dermis and epidermis with associated pruritus (itch). Urticaria is not a single disease but rather is a reaction pattern representing cutaneous mast cell degranulation. Urticaria (Hives)
• Angioedema Angioedema Angioedema is a localized, self-limited (but potentially life-threatening), nonpitting, asymmetrical edema occurring in the deep layers of the skin and mucosal tissue. The common underlying pathophysiology involves inflammatory mediators triggering significant vasodilation and increased capillary permeability. Angioedema
• Nonproductive cough
• Myalgias
• Arthralgias
• Abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
• Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea

Chronic schistosomiasis

Presentation can vary depending on the number of eggs in the tissues, the infection site, and the immune response of the host.

Intestinal schistosomiasis:

• Abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
• Decreased appetite
• Diarrhea Diarrhea Diarrhea is defined as ≥ 3 watery or loose stools in a 24-hour period. There are a multitude of etiologies, which can be classified based on the underlying mechanism of disease. The duration of symptoms (acute or chronic) and characteristics of the stools (e.g., watery, bloody, steatorrheic, mucoid) can help guide further diagnostic evaluation. Diarrhea
• Intestinal bleeding
• Complications:
  • Bowel strictures
  • Intestinal polyps and dysplasia

Hepatosplenic schistosomiasis:

• Hepatosplenomegaly
• Complications of portal hypertension Portal hypertension Portal hypertension is increased pressure in the portal venous system. This increased pressure can lead to splanchnic vasodilation, collateral blood flow through portosystemic anastomoses, and increased hydrostatic pressure. There are a number of etiologies, including cirrhosis, right-sided congestive heart failure, schistosomiasis, portal vein thrombosis, hepatitis, and Budd-Chiari syndrome. Portal Hypertension:
  • Esophageal varices (bleeding risk)
  • Pulmonary hypertension Pulmonary Hypertension Pulmonary hypertension (PH) or pulmonary arterial hypertension (PAH) is characterized by elevated pulmonary arterial pressure, which can lead to chronic progressive right heart failure. Pulmonary hypertension is grouped into 5 categories based on etiology, which include primary PAH, and PH due to cardiac disease, lung or hypoxic disease, chronic thromboembolic disease, and multifactorial or unclear etiologies. Pulmonary Hypertension (consequence of portosystemic collaterals allowing egg embolization to the lungs)
• Note: Liver function is not compromised.

Genitourinary schistosomiasis:

• Dysuria
• Urinary frequency
• Terminal hematuria (blood at the end of urine stream)
• Hemospermia
• Genital ulcerations
• Complications:
  • Ureteral strictures
  • Bladder neck obstruction 
  • Hydronephrosis Hydronephrosis Hydronephrosis is dilation of the renal collecting system as a result of the obstruction of urine outflow. Hydronephrosis can be unilateral or bilateral. Nephrolithiasis is the most common cause of hydronephrosis in young adults, while prostatic hyperplasia and neoplasm are seen in older patients. Hydronephrosis
  • Bladder cancer
  • Infertility Infertility Infertility is the inability to conceive in the context of regular intercourse. The most common causes of infertility in women are related to ovulatory dysfunction or tubal obstruction, whereas, in men, abnormal sperm is a common cause. Infertility (due to ovary or fallopian tube involvement)

Neuroschistosomiasis:

• Acute myelopathy
• Transverse myelitis
• Intracerebral lesions
• Multifocal encephalopathy

Diagnosis, Management, and Prevention

Diagnosis

• Microscopic examination of urine and stool for eggs
• Serologic testing:
  • ELISA
  • Indirect hemagglutination
  • Immunofluorescent antibody test
• Antigen testing:
  • Schistosome circulating antigen
  • Circulating cathodic antigen
  • PCR
• Parasite DNA DNA The molecule DNA is the repository of heritable genetic information. In humans, DNA is contained in 23 chromosome pairs within the nucleus. The molecule provides the basic template for replication of genetic information, RNA transcription, and protein biosynthesis to promote cellular function and survival. DNA Types and Structure testing (PCR)
• CT and MRI may show nonspecific changes for neuroschistosomiasis.

Management

• Anthelmintic therapy (praziquantel):
  • ↑ Calcium ion permeability in adult worms
  • Damage to the worm induces a host immune response.
• Corticosteroids to reduce inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation in:
  • Acute schistosomiasis syndrome
  • Neuroschistosomiasis

Prevention

Personal protection in endemic areas:

• Avoid swimming or wading in freshwater.
• Vigorously towel off after brief, accidental water exposure.
• Wear protective clothing and footwear.
• Boil bath water.

Control strategies:

• Sanitation programs (dispose of human urine and feces away from freshwater sources)
• Snail control
• Community-based mass-treatment programs

Differential Diagnosis

• Gastroenteritis Gastroenteritis Gastroenteritis is inflammation of the stomach and intestines, commonly caused by infections from bacteria, viruses, or parasites. Transmission may be foodborne, fecal-oral, or through animal contact. Common clinical features include abdominal pain, diarrhea, vomiting, fever, and dehydration. Gastroenteritis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the stomach Stomach The stomach is a muscular sac in the upper left portion of the abdomen that plays a critical role in digestion. The stomach develops from the foregut and connects the esophagus with the duodenum. Structurally, the stomach is C-shaped and forms a greater and lesser curvature and is divided grossly into regions: the cardia, fundus, body, and pylorus. Stomach and intestines, which is commonly caused by infections from bacteria Bacteria Bacteria are prokaryotic single-celled microorganisms that are metabolically active and divide by binary fission. Some of these organisms play a significant role in the pathogenesis of diseases. Bacteriology: Overview, viruses, or parasites. Clinical features include abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, diarrhea, vomiting, fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, and dehydration. Diagnostic testing with stool analysis or culture is not always required, but can help determine the etiology. Most cases are self-limited; therefore, the only required treatment is supportive therapy (fluids). 
• Inflammatory bowel disease (IBD): chronic inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the GI tract due to a cell-mediated immune response to the GI mucosa. Crohn’s disease and ulcerative colitis Ulcerative colitis Ulcerative colitis (UC) is an idiopathic inflammatory condition that involves the mucosal surface of the colon. It is a type of inflammatory bowel disease (IBD), along with Crohn's disease (CD). The rectum is always involved, and inflammation may extend proximally through the colon. Ulcerative Colitis are types of IBD. Symptoms include diarrhea, abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, weight loss, and extraintestinal manifestations. Diagnosis includes imaging, endoscopy, and biopsy. Management involves steroids, aminosalicylates, immunomodulators, and biologic agents.
• Viral hepatitis: liver Liver The liver is the largest gland in the human body. The liver is found in the superior right quadrant of the abdomen and weighs approximately 1.5 kilograms. Its main functions are detoxification, metabolism, nutrient storage (e.g., iron and vitamins), synthesis of coagulation factors, formation of bile, filtration, and storage of blood. Liver inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation caused by infection from a hepatitis virus Virus Viruses are infectious, obligate intracellular parasites composed of a nucleic acid core surrounded by a protein capsid. Viruses can be either naked (non-enveloped) or enveloped. The classification of viruses is complex and based on many factors, including type and structure of the nucleoid and capsid, the presence of an envelope, the replication cycle, and the host range. Virology: Overview. Patients may present with a viral prodrome of fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, anorexia, and nausea. Right upper quadrant abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, jaundice Jaundice Jaundice is the abnormal yellowing of the skin and/or sclera caused by the accumulation of bilirubin. Hyperbilirubinemia is caused by either an increase in bilirubin production or a decrease in the hepatic uptake, conjugation, or excretion of bilirubin. Jaundice, and transaminitis also occur. Diagnosis is made with viral serologic testing to differentiate viral hepatitis from schistosomiasis. Management of acute hepatitis is supportive.
• Acute pancreatitis Acute pancreatitis Acute pancreatitis is an inflammatory disease of the pancreas due to autodigestion. Common etiologies include gallstones and excessive alcohol use. Patients typically present with epigastric pain radiating to the back. Acute Pancreatitis: inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the pancreas Pancreas The pancreas lies mostly posterior to the stomach and extends across the posterior abdominal wall from the duodenum on the right to the spleen on the left. This organ has both exocrine and endocrine tissue. Pancreas. Patients present with a sudden onset of severe epigastric pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, which is typically sharp and radiates to the back. Acute pancreatitis Acute pancreatitis Acute pancreatitis is an inflammatory disease of the pancreas due to autodigestion. Common etiologies include gallstones and excessive alcohol use. Patients typically present with epigastric pain radiating to the back. Acute Pancreatitis is associated with alcohol abuse and gallstones. Diagnosis is based on abdominal pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, lipase elevation, and/or imaging (reveals pancreatic edema Edema Edema is a condition in which excess serous fluid accumulates in the body cavity or interstitial space of connective tissues. Edema is a symptom observed in several medical conditions. It can be categorized into 2 types, namely, peripheral (in the extremities) and internal (in an organ or body cavity). Edema). Management includes bowel rest, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain control, and IV fluid hydration.
• Contact dermatitis: an erythematous, papular dermatitis often with areas of vesiculation (due to direct skin Skin The skin, also referred to as the integumentary system, is the largest organ of the body. The skin is primarily composed of the epidermis (outer layer) and dermis (deep layer). The epidermis is primarily composed of keratinocytes that undergo rapid turnover, while the dermis contains dense layers of connective tissue. Structure and Function of the Skin exposure to an offending irritant with a direct cytotoxic effect). Diagnosis is based on history and physical exam findings. Management includes avoidance of offending irritants, adoption of protective measures, and the use of emollients and moisturizers. Topical steroids are the 1st-line intervention.
• Urinary tract Urinary tract The urinary tract is located in the abdomen and pelvis and consists of the kidneys, ureters, urinary bladder, and urethra. The structures permit the excretion of urine from the body. Urine flows from the kidneys through the ureters to the urinary bladder and out through the urethra. Urinary Tract infection: a wide spectrum disease ranging from simple cystitis to severe pyelonephritis Pyelonephritis Pyelonephritis is infection affecting the renal pelvis and the renal parenchyma. This condition arises mostly as a complication of bladder infection that ascends to the upper urinary tract. Pyelonephritis can be acute or chronic (which results from persistent or chronic infections). Typical acute symptoms are flank pain, fever, and nausea with vomiting. T Pyelonephritis and Perinephric Abscess. Depending on the location of the infection, patients can present with dysuria, urinary urgency/frequency, suprapubic pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, and/or fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever. Urinalysis and culture establish the diagnosis. Management options include oral or IV antibiotics. 
• Diphyllobothriasis Diphyllobothriasis Diphyllobothriasis represents an intestinal parasitic infection caused by the cestode Diphyllobothrium. Diphyllobothriasis is acquired by ingestion of late larvae in undercooked or raw fish. The clinical presentation of diphyllobothriasis varies from asymptomatic, nonspecific symptoms to intestinal obstruction, and/or vitamin B12 deficiency. Diphyllobothrium/Diphyllobothriasis: an intestinal parasitic infection caused by Diphyllobothrium Diphyllobothrium Diphyllobothriasis represents an intestinal parasitic infection caused by the cestode Diphyllobothrium. Diphyllobothriasis is acquired by ingestion of late larvae in undercooked or raw fish. The clinical presentation of diphyllobothriasis varies from asymptomatic, nonspecific symptoms to intestinal obstruction, and/or vitamin B12 deficiency. Diphyllobothrium/Diphyllobothriasis, a cestode, and acquired by ingestion of larvae in undercooked or raw fish from cold-water lake regions. Patients present with abdominal discomfort, diarrhea, glossitis, and anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview.  Diphyllobothriasis Diphyllobothriasis Diphyllobothriasis represents an intestinal parasitic infection caused by the cestode Diphyllobothrium. Diphyllobothriasis is acquired by ingestion of late larvae in undercooked or raw fish. The clinical presentation of diphyllobothriasis varies from asymptomatic, nonspecific symptoms to intestinal obstruction, and/or vitamin B12 deficiency. Diphyllobothrium/Diphyllobothriasis is diagnosed with microscopic examination of the stool for ova and parasites. Management includes anthelmintic therapy such as praziqunatel.
• Taeniasis Taeniasis Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis: a tapeworm infection occurring after consumption of raw or undercooked beef or pork. Patients are generally asymptomatic, but may present with the passage of proglottids. Taenia Taenia Taenia belong to the Cestoda class of helminths. Humans are infected with these tapeworms by eating undercooked beef (T. saginata) or pork (T. solium and T. asiatica). Taeniasis is often asymptomatic, but the ingestion of larvae can cause abdominal discomfort, nausea, and constipation or diarrhea. Taenia/Taeniasis solium presentation may rarely include seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures from neurocysticercosis. Diagnosis requires a high index of suspicion, a stool analysis (for ova and parasites), or imaging. Management includes anthelmintic therapy.