More cases could surface in the U.S. because of global travel to places with high infection rates
SAN FRANCISCO—Urinary schistosomiasis is a common infection in sub-Saharan Africa and the Mideast, and more cases could surface in the United States because of greater international travel and immigration from those regions, according to an infectious disease specialist.
Caused by a parasitic fluke, schistosomiasis frequently results in genitourinary morbidity and can lead to squamous cell carcinoma (SCC) of the bladder if not properly treated, said Charles King, MD, professor of international health at the Center for Global Health and Diseases at Case Western Reserve University School of Medicine in Cleveland. Many cases may elude early detection in North America, however, because cases seen here, so far, have been rare. He spoke here at the 46th annual Interscience Conference on Antimicrobial Agents and Chemotherapy.
Five Schistosoma species can cause human illness: S. haematobium, S. mansoni, S. japonicum, S. intercalatum, and S. mekongi. Of these, S. haematobium specifically hones in on the urinary tract, and can lead to chronic pelvic inflammatory disease, Dr. King said. Infection can persist for decades. It causes significant morbidity, but is associated with low mortality. There are an estimated 107 million cases in sub-Saharan Africa alone, Dr. King said.
Patients may present with acute schistosomiasis known as “snail fever” or a chronic infection with egg excretion. Some patients may be exposed but have no eggs on parasitology workups, he said. Known as a disease of poverty, most cases are traced to exposure to water contaminated with infected snails releasing cercariae, a stage in the worm’s life cycle. Snail fever not only causes fever but headache, myalgia, diarrhea, cough, weight loss, and urticaria. It is related to the early phases of parasite development in the human circulatory system.
The parasite is 1,000 times larger than defending phagocytes and, once it becomes established, is highly resistant to host immunity, Dr. King said. Schistosomes reproduce sexually, but do not multiply in human hosts. The average life span is four to six years. Severe disease occurs in just 1%-3% of cases.
Sequelae of infection
Classical sequelae of S. haematobium infection include hematuria, proteinuria, anemia, bladder deformity, dysuria, hydroureter, hydronephrosis, ascending bacterial superinfection, renal dysfunction, stone formation, and bladder cancer. Women may experience bilharzia cutanea tarda, vaginitis, dyspareunia, post-coital bleeding, pelvic inflammatory disease, cervical stenosis, ectopic pregnancy, and infertility. In men, common symptoms are prostatitis, seminal vesicle disease, painful ejaculation, hema-tospermia, and testicular pain.
SCC caused by schistosomiasis tends to be more aggressive and more advanced (T3 or T4) at the time of diagnosis. Although S. haematobium infection is linked to approximately 7% of bladder cancers in North America, it may cause up to 80% of bladder cancer cases where it is endemic.
To diagnose the infection, urologists may need to perform parasitology workups to detect eggs in urine or stool, a biopsy (via cystoscopy or rectal snip), or serology for anti-worm or anti-egg antibodies. The only effective medication currently available for this type of schistosomiasis is praziquantel 40 mg/kg orally as a single dose. Persisting infection should be tested for after two to three months, and occasionally treatment must be repeated two to three times to completely clear the infection. Repeat treatment is often required because early life cycle stages of the worms are not drug sensitive.
“It is easily treated and the diagnosis can be done with urine exam or blood tests. However, it takes four to six months for the symptoms to emerge following exposure, so often the connection is not made,” Dr. King told Renal & Urology News. “That is why travel history or immigrant background can be key to establishing the diagnosis.”