Clin Microbiol Infect 2010; 16: 225–231
In non-endemic countries, acute (invasive) schistosomiasis (AS) is typically seen in non-immune travellers, whereas chronic schistosomiasis is more frequently diagnosed in immigrants. Travellers with AS initially present with non-specific signs such as fever, cough, headache, and urticaria. Life-threatening cardiac and neurological complications may occur. The positive diagnosis of AS relies on seroconversion, which appears together with hypereosinophilia approximately 3 weeks after the onset of symptoms. When prescribed during AS, praziquantel usually does not prevent the chronic phase of the disease and is associated with exacerbation of signs and symptoms in approximately 50% of cases. According to the published literature, corticosteroids may be recommended alone or in association with praziquantel. When associated with corticosteroids, pharmacokinetic interactions may impair the efficacy of praziquantel. We suggest that corticosteroids should be restricted to use in patients with systemic complications of AS, whereas praziquantel should be initiated only when ova are detected in either stools or urine, depending on the culprit species.
Acute schistosomiasis (also called Katayama fever or syndrome) is one of the clinical manifestations of infection with Schistosoma sp. . It occurs several weeks after the penetration of schistosome cercariae through the skin, and is related to the migration of the larvae (schistosomulae) within the body. Oviposition, which defines the chronic phase of the disease, typically occurs weeks later. This symptomatic acute phase is mostly described in non-immune individuals (i.e. tourists) exposed to fresh water in endemic areas (Fig. 1) [1–3].
Acute schistosomiasis (AS) appears to be a more appropriate term than ‘Katayama fever’ for this disease. Katayama fever was described in 1847 in the Katayama district of Japan, and has been known to be caused by Schistosoma japonicum since 1904 [4,5]. It is of note that there is no longer schistosomiasis in the Katayama district as there is in the rest of Japan. In addition, all species of human schistosome can lead to AS in infected humans. There is thus no reason to use a name referring to S. japonicum or Japan in order to describe this disease. Finally, as fever is not always present in AS, the use of ‘fever’ in referring to the disease is not clinically relevant.
The recent report of a large series and clusters of AS in travellers with a single exposure allows us to better describe its natural history, pathophysiology, presentation, complications, diagnosis, and treatment.
In Europe, the Geosentinel Surveillance network reported 401 cases of travel-associated schistosomiasis seen within 11 years (1997–2008) in 27 sites in 12 Western countries, without making a distinction between acute and chronic schistosomiasis . In two European series of 257 and 1640 febrile travellers returning from abroad, AS was diagnosed in 1.6% and 1.7% of travellers, respectively [7,8]. In one of these series, AS was the third most common cause of febrile diseases imported from Africa, after malarial and rickettsial infections . In France, a retrospective study conducted between 2000 and 2004 in 42 parasitology laboratories found that 77 patients were diagnosed with AS . AS usually occurs sporadically or as small outbreaks [10,11].
Most cases of imported AS are described in travellers returning from West and East African countries such as Mali (Dogon country), Burkina Faso (Banfora falls), Ethiopia (National Park of Omo), Malawi Lake, and Zambia (Zambese Falls), from Brazil, and also from Laos [8,11–22]. Attack rates during outbreaks in tourists exposed while swimming in contaminated water vary from 39%  to 100%, but are usually above 65% [3,12,19].
One study showed relationships between the number of exposures, the duration of exposure and the risk of infection . Overall, infection is symptomatic in 54–100% of the non-immune infected travellers (Table 1). During the last two decades, AS has been more often reported in travellers infected with Schistosoma mansoni or Schistosoma haematobium than in those infected with S. japonicum or S. mekongi [6,9].
|Attack rate (%)||96||62||92||100||100||69||92||100||100||94||100||81|
|Country of infection||Mali||Mali||Burkina Faso||Malawi Mozambique||Ghana||Burkina Faso||Brazil||Brazil||Brazil||Brazil||Mali||Tanzania|
|Culprit species||Sh, Sm, Si||Sm||Sm||Sh||Sm||Sm||Sm||Sm||Sm||Sm||Sh||Sm|
|History of CD (%)||36||62.5||NA||13||20||5||100||NA||NA||100||94||13.6|
|Incubation period||2–10 weeks||NA||3–6 weeks||36 days||2–5 weeks||27 days||2–4 weeks||20 days||3–4 weeks||32 days||19 days||3–13 weeks|
|Acute schistosomiasis (%)||54||54||54||100||80||70||91||92||100||100||77||86|
Acute schistosomiasis is considered to be a toxaemic and allergic reaction to the migrating and maturing larvae of Schistosoma [1,25]. The severity of the clinical presentation varies according to the cercarial burden and the immune response to the released parasite antigens . Dry cough and angio-oedema, together with high counts of eosinophils, point to a type 1 hypersensitivity reaction.
Circulating immune complexes are found in c. 55–93% of patients with AS, and their presence is correlated with the intensity and severity of symptoms [27,28]. Moreover, direct toxicity of eosinophils seems also to play an important role . High counts of eosinophils are found during severe forms of AS. Major basic protein and eosinophil cationic protein, found in the eosinophil granules, are released during cell activation and could contribute to the severity of the disease by their direct toxicity, affecting vessels of the heart and brain [29,30]. A particular cytokine pattern, with high levels of proinflammatory cytokines (interleukin (IL)-1, IL-6, and tumour necrosis factor-α) and a poor Th2-type response (IL-4 and IL-5), has been described during AS. This cytokine pattern could explain the altered general status seen during AS .
These symptoms are typically seen before oviposition, egg-laying, and the appearance of granulomatous reactions around eggs, which defines the chronic phase of the disease. However, the two phases of the cycle may overlap, because an individual schistosomula may make several circuits in the pulmonary and systemic circulation before finding its way to the hepatic portal system . This explains why the delay between skin penetration of the cercariae and egg-laying may vary from one study to another. This is also illustrated by some studies that found eggs in stool or urine although some symptoms of AS were still present .
The most common signs of AS are fever, dry cough, weakness, headache, abdominal symptoms, and urticaria or angio-oedema (Fig. 2).
A history of exposure to contaminated water in endemic areas is essential. The disease is usually acquired while people are bathing in fresh water and, to a lesser extent, when they are crossing rivers or showering with contaminated water . Contact as brief as 1–5 min may be enough to allow transcutaneous penetration by cercariae [32,33]. A diffuse maculopapular pruritic skin eruption, named cercarial dermatitis, appears within 24 h after exposure. Pruritus alone may be the only sign . The eruption lasts for a few hours before disappearing spontaneously [1,34]. Therefore, a history of such an eruption can be found upon questioning, but it is rarely noticeable on the skin of returning travellers .
Reports of outbreaks in travellers with a single exposure have contributed to a better description of the natural history of schistosomiasis (Table 1). Cercarial dermatitis is reported in 5–100% of exposed travellers. The first symptoms of AS usually occur 2–6 weeks after exposure [11,14,25]. However, incubation periods from 1 to 12 weeks have been reported [8,13,35]. The main signs and symptoms are fever, cough, headaches and urticaria, but these may vary according to the infecting Schistosoma species (Table 2). Fever is frequent but usually mild. Fever above 39°C is seen in approximately one-third of cases , and appears approximately 19 days after exposure .
|Signs and symptoms (%)||Schistosoma mansoni |
|Schistosoma haematobium |
Nonetheless, this phase of schistosomiasis may be unapparent. Among 137 cases of schistosomiasis acquired during travel, clinical findings compatible with AS were found in 75 patients (66%). Thus, more than one-third of infected patients may have no signs of AS . As a consequence, individuals exposed to contaminated water should be investigated for schistosomiasis even in the absence of symptoms.
Neurological, pulmonary and cardiac complications can occur during AS, and some may be life-threatening. Neurological manifestations have been observed in c. 2% of cases of AS in the largest series conducted so far, during the Philippines campaign of 1944–1945 during World War II . Of the 1200 US soldiers infected with S. japonicum, 27 presented with neurological involvement during AS. Headache, disturbances of sensorium and weakness were all present, and c. 84% of the patients were febrile at one time or another; 44% presented with transient hemiplegia or tetraplegia; 60% complained of visual impairment; and 50% complained of incontinence, speech impairment, or ataxia. Neurological manifestations have also been described in travellers with AS caused by S. mansoni or S. haematobium infection [29,38]. The brain involvement during AS may be perceived as headache, confusion, seizures, loss of consciousness, focal deficiencies, visual impairment, ataxia, urinary incontinence, or motor paralysis [29,37,39–43]. In one of these cases, magnetic resonance imaging showed border-zone infarcts suggestive of cerebral vasculitis .
Cardiac injuries such as myocarditis, pericarditis or asymptomatic myocardial ischaemia have also been described during AS [29,44,45]. As was the case for neurological complications, the first description of cardiac complications was made during the Leyte campaign . An analysis of 315 electrocardiograms revealed various repolarization abnormalities: anomalies of T-waves (99%) or ST segments (52%). In addition, cardiac involvement has been described during an outbreak in Brazil . Among the 31 patients infected with S. mansoni, 12 (38.7%) had chest pain and six (19%) had a positive ultrasound diagnosis of pericarditis.
Pulmonary complications of AS are better described [47,48]. In a series of ten patients with AS, systematic chest computed tomography scan showed pulmonary nodules ranging in size from 2 to 15 mm, even in the absence of associated respiratory symptoms in as many as four patients . When patients have respiratory symptoms, chest X-rays show ill-defined pulmonary nodules. Pulmonary symptoms and radiographic abnormalities point to interstitial pneumonitis, similar to what is seen in tropical pulmonary eosinophilia. It is noteworthy that these severe forms can occur either during spontaneous evolution of the disease or after treatment with praziquantel [11,29,45,49].
The eosinophil count is usually above normal limits during AS. The onset of eosinophilia is delayed as compared with the onset of symptoms. Among 13 patients with AS, the mean delay between onset of fever and occurrence of hypereosinophilia was 21 days, whereas the delay between contaminating bathing and occurrence of hypereosinophilia was 47 days (range: 25–119 days) . In another series of 42 cases of AS, the eosinophil count was within normal limits in 27% . Therefore, the absence of eosinophilia does not rule out the diagnosis of AS.
Stool and urine analysis
Ova production begins at the end of adult maturation and migration to the vesical plexus or mesenteric veins, depending on the Schistosoma species, with at least 30–50 days from skin penetration to egg-laying . In the early stages of AS, a search for ova in stools or urine is typically negative, and will remain so until the end of the entire life cycle. Nonetheless, ova may still be detected in the urine or stools of patients complaining of symptoms compatible with AS. For example, among 23 patients with signs of AS, a search for ova in stools or urine at first investigation was positive in five (22%), laboratory examination being performed within 3 weeks of onset of fever . Overall, the period of egg detection varies from 5 to 10 weeks after exposure. Moreover, early treatment with praziquantel can delay egg-laying, as suggested by one study in which the mean delay between exposure and detection of ova was 196 days (range: 124–330 days) .
The diagnosis of AS relies on serological testing. Nonetheless, there are three things to keep in mind. First, serological findings are usually negative at the onset of clinical signs, and serological investigations must be repeated to identify seroconversion, which may appear up to 3 weeks (mean interval: 26 days) after the onset of symptoms, and c. 6 weeks (range: 27–100 days) after contact with contaminated water [11,25]. Therefore, upon primary investigation by a physician, serological findings are positive in no more than 65% of the cases [8,11].
Second, the sensitivity and specificity of serological tests vary with the antigens used; the tests are not uniform throughout the world; and most of the tests can be performed only in research laboratories. ELISA usually makes use of egg antigens (Schistosoma Egg Antigen/ELISA). It is indicated for the detection of schistosomiasis; however, sensitivity is no more than 50% [1,50]. Enzyme-linked immunotransfer blot is used for confirmation in the case of a positive ELISA result. This test is considered to be 100% specific, and results are usually available 4–6 weeks after exposure . When worm antigens are used, as in indirect haemagglutination tests, sensitivity reaches 70–90% for the diagnosis of AS according to the cut-off titre defining positivity . A combination of both ELISA and indirect haemagglutination gives 90% sensitivity and 92.9% specificity .
Moreover, infecting species identification cannot be performed with serological testing. For example, in one series of 22 patients infected with S. mansoni, serological cross-reactivity to S. haematobium was found in three patients, whereas only one patient was formally diagnosed as having S. mansoni by identification of ova in stool . According to outbreak reports, seroconversion and ova production may appear up to 6 months and 330 days after exposure, respectively [11,14].
ALAT rate is increased in c. 40–50% of cases, but to no more than five times above the normal upper limit [11,17]. Thrombocytopenia is seen in c. 10% of cases.
Corticosteroid treatment better than praziquantel treatment?
Treatment of AS is a real challenge, given that the efficacy of drugs varies according to the age of the schistosomulae [52–54]. Usually, the recommended dosage of praziquantel for chronic infection with S. mansoni or S. haematobium is 40 mg/kg once daily. Nonetheless, praziquantel is not effective during AS, and is sometimes associated with severe reactions [29,33,38,55]. It is ineffective on schistosomulae above 7 days of age [52,53], and does not prevent the chronic phase of the disease [11,36]. Indeed, in a series of 18 travellers, treatment with praziquantel during the incubation and acute phase of schistosomiasis was unable to prevent egg-laying and progression to a chronic stage . Furthermore, early treatment can worsen the symptoms of AS by inducing an allergic type of response to parasitic destruction [11,13,56]. This paradoxical reaction occurs in approximately 50% of patients treated for AS with praziquantel [8,11,56]. In some cases, this worsening of symptoms can be life-threatening by causing encephalitis related to vasculitis , myocarditis , or pulmonary events .
Considering that the pathophysiological mechanisms of AS result more from the immunological response to larvae migration than to the parasitic location, more and more authors recommend the use of corticosteroids [11,13,14,18,25,42,57]. According to them, praziquantel is used either in combination with corticosteroids [14,15,57] or following corticosteroid treatment [17,58]. Others, including ourselves, wait for egg-laying before using praziquantel [13,18]. It is of note that the use of corticosteroids decreases plasma levels of praziquantel by 50% . Praziquantel needs a good host-specific response against Schistosoma to be efficient [26,53]. During the early stage of AS, the weakness of the specific immune response might explain why praziquantel is not effective at this stage . Overall, the use of corticosteroids is discussed on a case-by-case basis after ruling out bacterial infection and strongyloïdosis [8,60].
Relapses of AS have also been described [8,61]. Relapsing forms, which occur after a median time period of 15 days after the end of the primary symptomatically similar episode, are treated with praziquantel and/or corticosteroids in an unknown proportion of patients [8,61].
Oxamniquine, arthemeter, and combined treatment
Oxamniquine (50 mg/kg once) could be indicated at the early phase of schistosomiasis, because it is more efficient against schistosomulae than praziquantel. Nonetheless, it is efficient only in the case of S. mansoni infection. When prescribed during the early stage (first week) of the infection or during AS, it prevents the occurrence of chronic S. mansoni infection and egg-laying [26,62,63].
Arthemeter, an artemisin derivative, is also efficient against schistosomulae aged 7–21 days . In one comparative trial performed in the Côte d’Ivoire, arthemeter reduced the incidence of S. mansoni infection by 50% in exposed children . Moreover, a 60–100% protective effect has been suggested in a Chinese population exposed to S. japonicum . A double-blind study comparing oral arthemeter and placebo in 322 exposed children in the Côte d’Ivoire showed a decrease in the incidence rate of S. haematobium by 65% as compared with 49% in the placebo group .
Combined therapy should also be considered . A combination of arthemeter and praziquantel showed a 99% reduction in egg burden, as compared with a 94% reduction with the use of praziquantel alone, in 88 and 89 children, respectively, treated in Gabon . Other antimalarial drugs, such as mefloquine, seem to have an antischistosomidae effect on mice [26,68].
Obviously, the best way to prevent AS is to avoid exposure to contaminated water in endemic areas. Otherwise, many topical ointments have been evaluated to protect swimmers from cercarial dermatitis. With the exception of N,N-diethyl-m-toluamide 50% ointment, none have given promising results; the use of sunscreens, copper salt, niclosamide, dimethyl phthalate-based or butylacetylaminopropionate-based ointments did not protect against Schistosoma infection . The use of petroleum jelly and vigorous drying with towels, with application of ethanol to exposed skin, has been proposed as an effective means of reducing cercarial penetration, but no study has demonstrated the effectiveness of this procedure [25,61]. In contrast, the use of N,N-diethyl-m-toluamide 50% ointment in 15 travellers at Lake Malawi was associated with the absence of infection during a 3-month follow-up period . Prior to being used for personal cleaning, contaminated water should be heated to 50°C for 5 min or treated with iodine or chlorine. Water can also be filtered with paper filters or left standing for 3 days before use .
The diagnosis and treatment of AS remains a challenge. Diagnosis relies mainly on positive serological testing. Treatment is based on corticosteroids in severe forms, and praziquantel should be initiated only when ova are detected in stools or urine, depending on the culprit species. Early treatment with oxamniquine (in the case of S. mansoni infection) or arthemeter shows promise and should now be evaluated in exposed travellers.
J. Saint Pierre is acknowledged for editorial assistance.
The authors declare no conflict of interest.