JOHNS HOPKINS
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Department of Pathology
600 N. Wolfe Street / Baltimore MD 21287-7093
(410) 955-5077 / FAX (410) 614-8087
Division of Medical Microbiology
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER Vol. 26, No. 10
Tuesday, June 05, 2007
A. Provided by Emily Luckman, Division of Outbreak Investigation, Maryland Department
of Health and Mental Hygiene.
There is no information available at this time.
B. The Johns Hopkins Hospital, Department of Pathology, Information provided by,
Zarir E. Karanjawala, M.D., Ph.D.
Case presentation: A 33 year-old man male who recently emigrated from Sierra Leone presented with a
six-month history of abdominal pain and a 3 day history of nausea and vomiting. Additionally, the patient
reported a 5-10 pound weight loss over a two-week period prior to admission. Laboratory data were
remarkable for leukopenia (1900/l) and thrombocytopenia (53,000/l). On physical exam, the patient
was afebrile and was noted to have a spleen extending 25 cm below the costal margin. A subsequent CT
scan demonstrated a nodular liver. A microscopic exam of the stool revealed the characteristic ova of
Schistosoma mansoni (see Figure).
Epidemiology: Schistosomiasis, first described in 1851 by Theodore Bilharz, affects over 200 million
individuals worldwide. Schistosomiasis is caused by trematode worms (schistosomes) that establish a
parasitic relationship within the venous system of their definitive hosts. The species most pathogenic in
humans are S. mansoni, S. hematobium, S. japonicum and S. intercalatum. Other species infrequently
account for human infections. S. mansoni is predominantly found in Brazil, Venezuela, the Caribbean,
Africa and the Middle East, S. hematobium in sub-Saharan Africa, and S. mekongi and S. japonicum in
East Asia. Despite control efforts, schistosomiasis continues to be prevalent and has continued to spread
to new areas. Recent epidemiological data shows that the expansion of schistosomiasis is related to
development of water resources and the migration of human populations. For example, the movement of
refugees led to the recent introduction of S. mansoni into Somalia.
Life cycle: Eggs are typically transmitted via human feces into freshwater. Subsequently the eggs hatch
releasing free-swimming miracidia, which penetrate the tissues of the Oncomelania species freshwater
snail. The miracidium matures within the snail resulting in hundreds of cercariae. The cercariae are
released from the infected snails, which act as an intermediate hosts in the life cycle. Cercariae are also
free-swimming and highly efficient at penetrating human skin with the aid of proteolytic enzymes. Once
in the subcutaneous tissues, the cercariae gain access to the blood, eventually reaching the portal
circulation, where they develop into adult male and female flukes. The male has a longitudinal genital
groove that serves as a receptacle for the female during copulation. Egg production typically begins 4 to 6
weeks after infection. Eggs are produced for the life of the worm, up to five years after the initial
infection. The female produces numerous eggs, which can be released into the feces. After the eggs
hatch, releasing numerous miracidia, the life cycle is complete.
Laboratory identification: Typically the diagnosis of schistosomiasis is made by identification of ova in
the stool or, in the case of S. hematobium, in the urine. The number of eggs shed into the stool can be
variable, thereby necessitating multiple samples to make the diagnosis. Ova are usually identifiable by
light microscopy; however, the size of the eggs depends on the species. S. mansoni eggs are similar in size
to S. hematobium and measure up to 180 x 60 m. The eggs of S. mansoni have a prominent lateral spine
unlike the terminal spine of S. haematobium. Da Silva et al. reported an ELISA utilizing a monoclonal
antibody against a 15 kDa antigen of S. mansoni worms with a reported 94% sensitivity.
Figure. Stool examination from this patient demonstrated
the characteristic ova for S. mansoni. A prominent lateral
spine is present. Courtesy of Dr. M. Britos.
Clinical aspects: Most schistosome adults reside within portal veins where they elicit a host response. The
adult worms, measuring up to 3 x 0.5 cm, may cause portal vein obstruction, and most tissue injury occurs
secondary to egg deposition into tissues. All 4 stages of clinical schistosomiasis may overlap, especially
with chronic exposure. After exposure to freshwater that contains cercariae, into the skin can produce a
localized urticarial reaction with a pruritis, “swimmer’s itch”, with a maculopapular rash within a few
hours. During the second stage, the schistosomes mature as they migrate to the portal system to produce the
“Katayama syndrome”, which includes an immune complex-mediated reaction with fever, malaise,
arthralgias, headache and prominent eosinophilia. Respiratory symptoms may be present in 70% of patients
and splenomegaly is reported in one-third of cases. The third stage is characterized by granulomatous
inflammation secondary to the deposition of eggs in the tissues, mostly in liver with S. mansoni infections;
however, the adrenal, brain, lung and skeletal muscle can also be involved. Eggs in the intestinal wall can
incite inflammation, ulceration, and microabscess formation that belie colicky abdominal pain, and in some
cases, bloody stools. The liver inflammation results in periportal and perisinusoidal fibrosis - the fourth
stage that with S. mansoni infections often results in cirrhosis, ascites and hepatosplenomegaly.
Manifestations of S. japonicum infection are similar to those of S. mansoni.
For S. haematobium, the worm migrates to the venous plexus of the urinary bladder, prostate, uterus and
vagina leading to hematuria. Chronic infections can cause pelvic pain and urgency. Eggs accumulated in
the bladder wall thereby cause urothelial hyperplasia, eventually fibrosis and strictures. The persistent
urothelial irritation can eventually result in squamous metaplasia, a process thought to be the precursor of
squamous cell carcinoma of the bladder, which occurs at a high frequency in S. haematobium-infected
individuals.
References:
Ross et al., (2002); N Engl J Med 346:1212-1220.
Koneman et al., Color Atlas and Textbook of Diagnostic Microbiology, 6th edition, Lippincott, Philadelphia,
2006.
Mandell et al., Principles and practice of infectious disease. 6th edition, Churchill-Livingstone, 2005.