Schistosomiasis in a returning international traveler with cyclic fevers and diarrhea

Discussion

There are 5 important species of Schistosoma: intestinal Schistosoma consisting of S mansoni, Schistosoma japonicum, Schistosoma intercalatum, and Schistosoma mekongi, and urogenital Schistosoma haematobium.³ The life cycle of the trematode begins in fresh water where the miracidia, which are released from eggs in the feces of individuals infected with the schistosome, penetrate specific snails as an intermediate host (Figure 3).⁴ Cercariae from the snails are then released back into the water and penetrate the skin of humans, where they migrate to the venous system of either the gastrointestinal or the genitourinary tract.⁴

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Figure 3.

Life cycle of Schistosoma species

Reproduced from the Centers for Disease Control and Prevention.⁴

Acute schistosomiasis syndrome is characterized by symptoms of fever, diarrhea, abdominal pain, headache, myalgia, and cough, and occurs between 3 and 8 weeks after infection.⁵ Only one or a few of these symptoms might be present. Chronic infection in intestinal disease is manifested by abdominal pain, diarrhea, hematochezia or melena, or hepatosplenomegaly. Chronic urogenital schistosomiasis has clinical symptoms such as hematuria, genital lesions, and vaginal bleeding, and can lead to genitourinary tract organ fibrosis and bladder cancer.

Schistosomiasis is most commonly diagnosed by detecting parasite eggs in stool or urine specimens or through rectal biopsy.¹ Tests not used as routinely are antibody and antigen tests in blood or urine samples.⁶ Less often, tests include serology, antigen detection, and molecular DNA polymerase chain reaction assays. Other potential laboratory findings include eosinophilic leukocytosis, thrombocytopenia, anemia, positive hemoccult stool findings, and hematuria. Treatment is with praziquantel, an anthelmintic agent. The treatment dosage varies from 40 mg/kg per day orally in 2 divided doses for 1 day, to 60 mg/kg per day orally in 3 divided doses on 1 day depending on the species being treated. Public health officials are working hard to eradicate and control spread of the disease through access to safe water, improved sanitation, hygiene education, and snail control.¹

Illness, particularly fever, in returning travelers is a common clinical challenge for family physicians. Differential diagnoses include the common mosquito diseases of malaria and dengue fever; the rickettsial diseases such as typhus; and the water- and food-borne bacterial infections of typhoid and paratyphoid fevers. Common infections, such as respiratory, urinary, or skin infections, should, as always, be considered. Recurrent fevers are always treated as malaria until proven otherwise.

Although the history of this case was suggestive of Schistosoma infection, there were several aspects that made it unique: the previous treatment with praziquantel and the lack of positive stool findings.

In the history, the patient reported having taken a dose of praziquantel after exposure to a known Schistosoma-infested lake while abroad. The amount of praziquantel he received is unknown, as is whether the treatment was accurate in dosage and efficacy. Antibiotics and other medications abroad might lack the same potency and efficacy that they have in North America, which has strict governmental regulation policies.⁷ The potential for the medicine this patient received to have been expired or of low potency exists. In addition to potential drug ineffectiveness, there is also specific timing for treatment of schistosomiasis. The incubation period of schistosomiasis ranges from 14 to 84 days, and praziquantel is most effective against the adult worm, which requires an established antibody response to the parasite.⁶ Treatment typically should occur 6 to 8 weeks after exposure to contaminated water.⁶ The patient was initially treated within the first week after exposure, so perhaps the treatment would have not been effective, as it was not yet directed against adult worms. Most of the disease can be eradicated with 1 course of treatment, but patients with a heavy disease burden might require retreatments 2 to 4 weeks after the initial dose.⁶ Follow-up after initial treatment includes monitoring for re-emergence of clinical manifestations. Symptom resolution, eosinophilia resolution, and negative stool findings are indicators of disease eradication. Persistence of viable eggs requires repeated treatment.⁷

Another area of diagnostic concern was the consistent lack of findings from the stool studies. We tested a total of 5 stool ova and parasite excavations and none had positive findings. According to the Centers for Disease Control and Prevention and other tropical disease information sources,⁸ eggs should be available for detection on a simple smear (1 to 2 mg of fecal material). As eggs can be passed intermittently or in small amounts, specificity is enhanced by performing multiple examinations by using the formalin–ethyl acetate technique to increase the concentration, or by using the Kato-Katz technique (20 to 50 mg of fecal material) or the Ritchie technique (suspension of approximately 2 g of stool in 10 mL of water at 45°C followed by filtration, centrifugation, and microscopic evaluation).⁹ It is also suspected that egg excretion occurs with a circadian rhythm peaking at noon, so samples should be collected between 10:00 am and 2:00 pm.⁹ As in this case, if eggs cannot be identified on stool tests, a rectal biopsy should be performed with multiple samples taken. In this case, the histologic sample provided the definite diagnosis.