BASICS
DESCRIPTION
- Flatworm infection (trematodes) of the genus Schistosoma
- Commonly presents as a swimmer 's itch and maculopapular rash
- Katayama fever (acute schistosomiasis) is a systemic reaction to the parasite in the bloodstream.
- Chronic disease is primarily caused by tissue migration of Schistosoma eggs. Immune response causes inflammation and scarring. Primarily occurs in gastrointestinal and/or genitourinary tracts
EPIDEMIOLOGY
Prevalence
- >230 million people infected worldwide (1)
- Schistosomiasis is endemic in Africa (primarily) but also in Asia and South America (1).
ETIOLOGY AND PATHOPHYSIOLOGY
- Schistosoma mansoni (Africa, South America), Schistosoma japonicum (China, Philippines, Indonesia), and Schistosoma haematobium (sub-Saharan Africa, Middle East) are the most common organisms in human schistosomiasis (1). Two other species may also cause disease: Schistosoma intercalatum (Central Africa), and Schistosoma mekongi (Laos and Cambodia).
- Infection occurs in warmer climates (<1,800 m elevation) due to temperature requirements of the reservoir (snails).
- Adult worms live in the human mesenteric veins (S. mansoni and S. japonicum) or perivesicular veins around the bladder (S. haematobium) (2).
- A fully matured female releases hundreds to thousands of eggs daily (2). Eggs migrate through the blood vessel walls and into the surrounding tissue by secreting proteolytic enzymes and gradually making their way into the intestinal lumen (S. mansoni and S. japonicum) and into the bladder (S. haematobium) lumen (2). Eggs are then excreted in feces or urine (2).
- On contact with fresh water, miracidia are released from the egg and seek out species-specific intermediate freshwater snail hosts (2). Within the snail, miracidia multiply asexually (2).
- After 4 to 6 weeks, free-swimming cercarial larvae are released with a lifespan of <48 hours (2).
- After contacting human skin or mucosal surfaces, cercariae penetrate through the tissue and into the bloodstream, eventually migrating to the portal vein. Over the next 4 to 6 weeks, they mature, mate, and migrate to their final destination (mesenteric or venous plexus of the bladder) (2).
- Eggs entrapped in the tissues during migration cause chronic disease through an inflammatory response that produces fibrosis and calcification (2).
- Severity of symptoms relates to the burden of infection and host immune response (2).
- Genitourinary disease (S. haematobium) is caused by irritation of the bladder and/or ureteral walls (2).
- Gross and microscopic hematuria is common, especially in children. Ureteral stenosis can cause hydronephrosis and eventual renal failure. Bladder cancer is increased in patients with schistosomal infections, either due to chronic inflammation or altered carcinogen (tobacco, etc.) susceptibility (2).
- Deposition of eggs in the female reproductive tract can lead to infertility (2).
- Hepatic periportal inflammation, especially in early disease, can cause hepatosplenomegaly. Years of chronic inflammation can lead to fibrosis, portal hypertension, and splenomegaly or varices (1).
- Neuroschistosomiasis (the most serious form of schistosomal infection) can occur when eggs or adult worms cause meningeal inflammation (2).
- Genital schistosomiasis (S. haematobium) has been associated with HIV infection in sub-Saharan African women (1).
- Egg excretion may take 40 to 50 days after initial infection.
RISK FACTORS
Exposure to contaminated freshwater in endemic areas � �
GENERAL PREVENTION
- Avoid drinking, bathing, or swimming in untreated freshwater in endemic areas.
- Boil water for at least 1 minute prior to drinking, or use appropriately filtered water.
- Water held in storage for 48 hours may generally be used for bathing.
- Iodine treatment may not rid water of all larvae.
- Proper community-based sanitation. Control of the freshwater snails that serve as intermediate hosts is not as effective; environmental effects of chemicals used to eliminate snails can have unintended consequences (2).
- Mass treatment of high incidence populations is helpful. Retreatment is often necessary as recurrence is high (53%).
- There is no current vaccine.
DIAGNOSIS
HISTORY
- Infections are frequently asymptomatic.
- Travel history to endemic areas (2)
- Rash and itching (localized, usually feet/lower extremity) may present soon after exposure to contaminated freshwater as a manifestation of larval skin penetration (1). More common in individuals with repeated freshwater exposures
- Katayama fever (an acute systemic reaction to Schistosoma in the bloodstream and to egg deposition in the tissues) may present a few weeks after exposure. More common in nonimmune (1)
- Other symptoms (often mild, may last days to weeks):
- Fatigue, fever, or malaise
- Myalgias, arthralgias
- Nonproductive cough
- Abdominal discomfort, bloating, rectal bleeding, diarrhea, nausea, vomiting, or anorexia
- Hematuria (S. haematobium)
- Angioedema
- Headache, seizures, focal CNS impairment (neuroschistosomiasis)
- Myelopathy (acute transverse myelitis) most common neurologic manifestation of S. mansoni or S. haematobium infection. Acute encephalitis is typical of S. japonicum.
PHYSICAL EXAM
- A pruritic, papular rash may be seen hours to days after initial larval exposure (2).
- Hepatomegaly and splenomegaly in acute or chronic phase (1)
- S. haematobium infections can cause nonspecific genital lesions in women (1).
- Neurologic findings (neuroschistosomiasis); findings are specific to the type and location of lesions.
DIFFERENTIAL DIAGNOSIS
- Malaria
- Viral hepatitis
- Leishmaniasis
- Inflammatory bowel disease
- Gastroenteritis
- UTI
- Urogenital cancer
DIAGNOSTIC TESTS & INTERPRETATION
Initial Tests (lab, imaging)
- Microscopic exam of stool or urine to identify viable eggs is the gold standard for diagnosis (1).
- Efforts to concentrate eggs in stool or urine help quantify infections (2)[B].
- CBC may show anemia and eosinophilia (1).
- Urinalysis may show hematuria in S. haematobium infections (1). Urine antigen testing for S. haematobium
- Antibody tests may distinguish between active or remote infection. Negative serologic tests help rule out infection. Positive tests may indicate infection in travelers (1).
- PCR (not readily available) is more sensitive and specific, particularly in early stages of infection as well as for light infections (3).
- Chest radiograph may show infiltrates (4).
- Ultrasound for liver, spleen, kidney, bladder, and ureteral involvement (4)
- Consider MRI or CT if neurologic symptoms are present (4). A definitive diagnosis of neurologic schistosomiasis can only be made histopathologically. Positive stool or serologic studies support the diagnosis.
- Other
- Eggs may on tissue biopsy (rectal tissue) (4).
- Colonoscopy and intestinal biopsies identify cases of chronic intestinal schistosomiasis, particularly in patients with no obvious exposure (5)[C].
TREATMENT
GENERAL MEASURES
- Bathing; water precautions to avoid infection
- WHO recommends periodic mass treatment to reduce morbidity in highly endemic areas (2).
MEDICATION
First Line
- Praziquantel: 40 mg/kg as a single dose with a repeat dose in 4 to 6 weeks (6)[A]. Higher doses; 60 mg/kg divided into 3 doses q4h for S. japonicum or S. mekongi (1)[A]
- May be used to treat children >4 years old. May be used in pregnant women. Lactating mothers will need to stop breastfeeding on the day of treatment and for 3 days after (4)[C].
- Clinically relevant resistance has not been shown.
- Repeat dosing is needed to eradicate younger parasites. Average deworming response is 60 " �90% with a single treatment.
- Prednisone: 1.5 to 2 mg/kg/day for 3 weeks for Katayama fever or neuroschistosomiasis (in addition to praziquantel) (4)[C].
Second Line
- Oxamniquine: 40 mg/kg (6)[A]
- In vitro resistance to praziquantel has been demonstrated. Medications that are currently being investigated are triclabendazole, artemisinins, and tribendimidine (1).
ISSUES FOR REFERRAL
- Evidence of intracranial hypertension or intractable seizures (cerebral schistosomiasis)
- Difficulty in establishing accurate diagnosis
ONGOING CARE
PATIENT EDUCATION
- Prevention strategies in endemic areas.
- Travelers to endemic areas should be counseled to avoid bathing or swimming in untreated fresh water.
PROGNOSIS
Prognosis is good if identified and treated early. � �
COMPLICATIONS
- Portal hypertension, esophageal varices, and GI bleeding
- Hepatic fibrosis (may be genetically linked)
- Infertility
- Renal failure secondary to urethral stenosis and hydronephrosis
- Thrombocytopenia secondary to splenomegaly and sequestration
- Anemia from bleeding via intestinal ulcers or esophageal varices
- Pulmonary hypertension and subsequent heart failure
- Bladder cancer
- Malnutrition
- Death
REFERENCES
11 Colley � �DG, Burstinduy � �AL, Secor � �WE, et al. Human schistosomiasis. Lancet. 2014;383(9936):2253 " �2264.22 Gryseels � �B, Polman � �K, Clerinx � �J, et al. Human schistosomiasis. Lancet. 2006;368(9541):1106 " �1118.33 Van Meensel � �B, Van Wijngaerden � �E, Verhaegen � �J, et al. Laboratory diagnosis of schistosomiasis and Katayama syndrome in returning travelers. Acta Clin Belg. 2014;69(4):267 " �272. doi:10.1179/2295333714Y.0000000039.44 Gray � �DJ, Ross � �AG, Li � �YS, et al. Diagnosis and management of schistosomiasis. BMJ. 2011;342:d2651.55 Ye � �C, Tan � �S, Jiang � �L, et al. Endoscopic characteristics and causes of misdiagnosis of intestinal schistosomiasis. Mol Med Rep. 2013;8(4):1089 " �1093. doi:10.3892/mmr.2013.1648.66 Danso-Appiah � �A, Olliaro � �PL, Donegan � �S, et al. Drugs for treating Schistosoma mansoni infection. Cochrane Database Syst Rev. 2013;(2):CD000528.
ADDITIONAL READING
- Caffrey � �CR. Schistosomiasis and its treatment. Future Med Chem. 2015;7(6):675 " �676.
- Chai � �JY. Praziquantel treatment in trematode and cestode infections: an update. Infect Chemother. 2013;45(1):32 " �43.
- Dessein � �A, Arnaud � �V, He � �H, et al. Genetic analysis of human predisposition to hepatosplenic disease caused by schistosomes reveals the crucial role of connective tissue growth factor in rapid progression to severe hepatic fibrosis. Patho Biol (Paris). 2013;61(1):3 " �10.
- Masaku � �J, Madigu � �N, Okoyo � �C, et al. Current status of Schistosoma mansoni and the factors associated with infection two years following mass drug administration programme among primary school children in Mwea irrigation scheme: a cross-sectional study. BMC Public Health. 2015;15:739.
- Meurs � �L, Brienen � �E, Mbow � �M, et al. Is PCR the next reference standard for the diagnosis of Schistosoma in stool? a comparison with microscopy in Senegal and Kenya. PLoS Negl Trop Dis. 2015;9(7):e0003959.
- Nascimento-Carvalho � �CM, Moreno-Carvalho � �OA. Neuroschistosomiasis due to Schistosoma mansoni: a review of pathogenesis, clinical syndromes and diagnostic approaches. Rev Inst Med Trop Sao Paulo. 2005;47(4):179 " �184.
- Ross � �AG, McManus � �DP, Farrar � �J, et al. Neuroschistosomiasis. J Neurol. 2012;259(1):22 " �32.
CODES
ICD10
- B65.9 Schistosomiasis, unspecified
- B65.1 Schistosomiasis due to Schistosoma mansoni
- B65.2 Schistosomiasis due to Schistosoma japonicum
- B65.8 Other schistosomiasis
- B65.0 Schistosomiasis due to Schistosoma haematobium
- B65.3 Cercarial dermatitis
ICD9
- 120.9 Schistosomiasis, unspecified
- 120.1 Schistosomiasis due to schistosoma mansoni
- 120.2 Schistosomiasis due to schistosoma japonicum
- 120.8 Other specified schistosomiasis
- 120.0 Schistosomiasis due to schistosoma haematobium
- 120.3 Cutaneous schistosomiasis
SNOMED
- Infection by Schistosoma (disorder)
- Schistosoma mansonii infection (disorder)
- Schistosoma japonicum infection (disorder)
- cutaneous schistosomiasis (disorder)
- Schistosoma haematobium infection (disorder)
CLINICAL PEARLS
- Suspect schistosomiasis in travelers to endemic areas presenting with symptoms of Katayama fever (malaise, abdominal pain, fatigue, myalgias).
- Schistosomiasis may present as "swimmer 's itch. " �
- Consider schistosomiasis in the differential diagnosis for returning travelers presenting with fever, abdominal pain, and diarrhea.
- Praziquantel is the treatment of choice.