Answer: Schistosoma haematobium. Based on the morphological characteristics of the organism seen in the cytology smear and the bladder tissue biopsy specimen, the patient was diagnosed with an infection caused by Schistosoma haematobium. While the cytology examination was diagnostic for this patient, the clinical team chose to further confirm with a biopsy. The patient recovered on praziquantel therapy with normal urine and three follow-up negative urine cytology specimens.
Schistosoma species are among the most medically important trematodes, with the greatest impact on human health. In 2014, the World Health Organization reported 61.6 million cases of schistosomiasis requiring treatment worldwide (http://www.who.int/mediacentre/factsheets/fs115/en/). The three major species of Schistosoma infecting humans are S. haematobium, S. mansoni, and S. japonicum. The life cycle of all species of Schistosoma is composed of five developmental stages: egg, miracidium, sporocyst, cercariae, and adult worm (http://www.cdc.gov/dpdx/schistosomiasis/index.html). Transmission to humans is via penetration of the skin by the free-swimming cercariae, which depend on the presence of freshwater snails as the intermediate host. The geographic distributions of the different species are dependent on their specific freshwater snail intermediate host: S. mansoni is found in Africa and Latin America, S. haematobium in Africa and the Middle East, and S. japonicum in Asia.
Schistosomes have tropism for different areas of the body. The adult worms of S. mansoni and S. japonicum reside in the mesenteric venules, where they lay eggs that are progressively moved toward and deposited in the intestine or the liver, causing gastrointestinal or liver disease, respectively. Alternatively, S. haematobium affects the urinary tract, with the adult worm most commonly living in the venous plexus of the bladder, with eggs deposited in the bladder wall and ureters. Clinically, most patients are asymptomatic but may become symptomatic, especially immunocompromised patients. The acute stage begins shortly after cercarial penetration, with itching and dermatitis followed by fever, chills, diarrhea, fatigue, abdominal pain, hematuria (with S. haematobium), and hepatosplenomegaly. The chronic stage is associated with significant morbidity and mortality due to reaction of tissues to schistosome egg deposition, causing granuloma formation and fibrosis. In the case of Schistosoma haematobium infection, this can lead to squamous cell carcinoma of the bladder (1).
Direct parasitological examination of either stool or urine remains the gold standard for diagnosis. The cytology examination of this patient demonstrated the classic oval-shaped S. haematobium egg (typical size, 110 to 170 μm by 40 to 70 μm) with a terminal spine and a hatching ciliated miracidium. Hatching of the miracidium from the egg is a process rarely seen in routine microbiology specimens. It is hypothesized that different specimen-processing techniques in the cytology laboratory may provide optimal conditions to promote miracidium hatching. As urine samples are commonly encountered in cytology, the diagnosis of S. haematobium infection should be thought of in the correct clinical context (2). The eggs of the other two species also have their own distinct features: S. mansoni eggs (115 to 175 μm by 45 to 70 μm) are oval in shape with a sharp lateral spine, and S. japonicum eggs (70 to 100 μm by 50 to 70 μm) are round with a rudimentary lateral spine (http://www.cdc.gov/dpdx/schistosomiasis/index.html). Direct examination has many limitations, and for this reason, serological testing can also be useful. There are currently ongoing efforts to design methods for earlier diagnosis (3). Praziquantel is the treatment of choice for schistosomiasis. Efforts to reduce transmission of schistosomiasis include mass drug administration, proper disposal of human waste, access to clean water, eradiation of the snail host, and avoidance of swimming in areas of endemicity (4).
See https://doi.org/10.1128/JCM.00724-16 in this issue for photo quiz case presentation.
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