Schistosomiasis is caused by parasitic worms inhabiting the gastrointestinal or renal tract
Larvae released into fresh water by infested snails penetrate the skin of people coming into contact with the contaminated water. Even brief exposure can lead to infestation. After entering the body, the adult worms live in blood vessels and the females release eggs. Some eggs are passed out of the body in the urine or faeces but others become trapped in body tissues, causing an immune reaction.2 Adult worms can live for decades in the body.2,3
Schistosomiasis is often asymptomatic
Schistosomiasis is often asymptomatic. A pruritic rash may develop soon after the larvae penetrate the skin. In the following months an individual may develop Katayama fever (sudden fever, fatigue, myalgia, malaise, cough, weight loss, eosinophilia, abdominal pain, diarrhoea and haematuria).2,4 Katayama fever is more common in travellers; it is rare among those living in endemic areas.2
Chronic untreated schistosomiasis progressively damages the bladder, ureters and intestines as well as causing enlargement of the liver and spleen. It may eventually lead to kidney failure or bladder cancer.2,3,5
Schistosomiasis is endemic in Africa and parts of south-east Asia
Schistosomiasis occurs throughout tropical and subtropical regions (Table 1) but the greatest burden of illness is in Africa.3Up to 41% of recently arrived African refugees have positive serology for schistosomiasis.3
Box 1 Areas of endemic schistosomiasis6,7
Throughout Africa: highest risk in southern and sub-Saharan Africa
Cambodia, Laos, Philippines, Southern China
Egypt, Iran, Iraq, Oman, Saudi Arabia, Yemen
South America & Caribbean
Brazil, Dominican Republic, Suriname, Venezuela
Diagnosis of schistosomiasis
The diagnostic 'gold standard' for schistosomiasis is the examination of the faeces or urine for eggs. However, this may require multiple samples and on its own may not detect a light-to-moderate worm burden. For this reason, diagnosis often relies on serology.3
Positive serology does not distinguish between current and past infection. However, most new arrivals to Australia with positive serology are probably infected, as the worms can survive for decades and individuals in endemic areas are repeatedly infected.3
For travellers returning from endemic regions, a positive antibody response will only be detected more than 6 weeks after initial infection.8
In people with equivocal serology the specimen should be re-tested using a different serological method.3 If the result remains equivocal, treat the individual as if it was positive.
Treat with 2 doses of praziquantel 4 hours apart
Current Australian guidelines recommend 2 doses of praziquantel 4 hours apart in people with positive serology. For people infected anywhere except south-east Asia, each dose should be praziquantel 20 mg/kg.3,9 This dosage regimen has been shown in systematic reviews to be effective and well tolerated.3 For people infected in south-east Asia, each dose should be praziquantel 30 mg/kg.3
Each dose should be taken after food. The tablets can be broken into four pieces to ensure accurate dosing but should not be chewed because of their bitter taste.10,11
The praziquantel product information recommends an alternative dosage regimen of 3 doses of praziquantel, 20 mg/kg, 4 hours apart.11 This dosage regimen is the same irrespective of country of infection.
Praziquantel is available as 600 mg tablets, with a maximum of 8 tablets. This will be sufficient for most individuals. However, if prescribing for a person infected in south-east Asia who weighs ≥ 80 kg, you will need to request an increase in the maximum quantity.*
Praziquantel is only active against adult worms.2,8 In recently infected people, who are likely to have immature worms, a second round of treatment with praziquantel several weeks later may be necessary.8
*If using the 3-dose regimen specified by the product information, any individual who weighs ≥ 80 kg will require an increase to the maximum quantity.
Check for eggs in all people with positive serology
In addition to treatment with praziquantel, all people with positive (or equivocal) serology should be examined for eggs to identify those with a high worm burden.3
If eggs are present in the faeces, check for indicators of end-organ damage† and refer to a specialist if necessary. Repeat the faecal examination in 3 months and prescribe another dose of praziquantel if eggs are still present.3
Perform a urinalysis to check for blood and, if positive, request urine microscopy to check for eggs. If eggs are present in the urine check for a history of recurrent urinary tract infections, evidence of genital lesions or hydronephrosis, and perform a renal ultrasound. Refer to a urologist if necessary. Repeat the urine examination in 3 months and prescribe another dose of praziquantel if eggs are still present.3
If there are no eggs but the individual has eosinophilia, perform a full blood count after 3 months and investigate further if eosinophilia is still present.3
†History of chronic liver disease, gastrointestinal haemorrhage, hepatomegaly, splenomegaly, ascites, positive hepatitis B or C serology, thrombocytopenia, low albumin or raised liver enzyme concentration.
Adverse effects are mainly caused by dying worms
Common adverse effects with praziquantel include dizziness, headache, malaise, drowsiness, nausea, vomiting, abdominal pain and diarrhoea.2,3,10 Many are thought to be caused by immune responses to the dying worms.3,10Symptoms are usually mild and transient. However, there have been occasional reports of acute colic with bloody diarrhoea in heavy infections.2,12,13
There is limited information on use of praziquantel in pregnant and lactating women.3,10 In endemic areas the WHO advises that the health advantages of treating pregnant women outweigh the risks to their health and to the health of their babies.14 Withhold treatment during the first trimester but offer it in the second or third trimester or during lactation, after discussing its risks and benefits with the patient.3,10
The federal government provides assistance for refugee health assessments
Medicare Benefits Schedule (MBS) item numbers 714 and 716 reimburse general practitioners who perform refugee and humanitarian entrant health assessments within 12 months of the patient's arrival in Australia.
Refugee health assessments should always be undertaken with an appropriate interpreter, preferably someone who is not known to the patient personally.3 The Telephone Interpreting Service (TIS) is available free of charge to general practitioners who provide a Medicare service to non-English speaking permanent residents or Australian citizens. Call the TIS Doctors' Priority Line (1300 131 450) to access this service.15
- Pharmaceutical Benefits Advisory Committee. Positive Recommendations made by the PBAC \u2014 March 2009. Canberra: Australian Government Department of Health and Ageing, 2009. http://www.health.gov.au/internet/main/publishing.nsf/Content/pbacrec-mar09-positive (accessed 26 May 2009).
- Gryseels B, Polman K, Clerinx J, et al. Human schistosomiasis. Lancet 2006;368:1106-18. [PubMed]
- Australasian Society for Infectious Diseases Refugee Health Guidelines Writing Group. Diagnosis, management and prevention of infections in recently arrived refugees. Sydney: Australasian Society for Infectious Diseases, 2009
- CDC Division of Parasitic Disease. Parasites and Health: schistosomiasis. Atlanta: Centre for Disease Control and Prevention, 2008. http://www.dpd.cdc.gov/dpdx/HTML/Schistosomiasis.htm (accessed 27 May 2009).
- World Health Organization. Schistosomiasis: Epidemiological situation 2007. http://www.who.int/schistosomiasis/epidemiology/en/ (accessed 26 May 2009).
- World Health Organization. Schistosomiasis: countries or areas at risk, 2007 2008. http://gamapserver.who.int/mapLibrary/Files/Maps/Global_ShistoPrevalence_ITHRiskMap.png (accessed 26 May 2009).
- World Health Organization. Fact sheet N\u00b0115: Schistosomiasis. 2007. http://www.who.int/mediacentre/factsheets/fs115/en/ (accessed 26 May 2009).
- Corachan M. Schistosomiasis and international travel. Clin Infect Dis 2002;35:446\u201350. [PubMed]
- Antibiotic Writing Group. Therapeutic Guidelines: Antibiotic. Version 13. Melbourne: Therapeutic Guidelines Ltd, 2006.
- Rossi S, ed. Australian Medicines Handbook 2009. Adelaide: Australian Medicines Handbook Pty Ltd, 2009.
- Bayer Australia Ltd. Biltricide product information. 27 May 2008. Australia: 2008.
- Polderman AM, Gryseels B, Gerold JL, et al. Side effects of praziquantel in the treatment of Schistosoma mansoni in Maniema, Zaire. Trans R Soc Trop Med Hyg 1984;78:752\u20134. [PubMed]
- Watt G, Baldovino PC, Castro JT, et al. Bloody diarrhoea after praziquantel therapy. Trans R Soc Trop Med Hyg 1986;80:345\u20136. [PubMed]
- World Health Organization. Preventive chemotherapy in human helminthiasis : coordinated use of anthelminthic drugs in control interventions : a manual for health professionals and programme managers. Geneva: WHO, 2006. http://whqlibdoc.who.int/publications/2006/9241547103_eng.pdf (accessed 29 June 2009).
- Department of Immigration and Citizenship. Free interpreting services. Australian Government, 2009. http://www.immi.gov.au/living-in-australia/help-with-english/help_with_translating/free-services.htm (accessed 26 May 2009).