Question

A 40 yr old man presents for a routine examination. He appears well but complains of some mild dysuria and increasing frequency of urination. He has never had a UTI and thought that the increasing urination was a normal part of aging. He has not seen any blood in his urine but indicates his urine is darker than usual. He smokes a pack a day and was a recent immigrant from Egypt who has lived in the U.S. for the past 3 years.

1. What are some parasitic organisms that could be the cause of this disease?

2. What are some tests that would be ordered to look for the parasites above? Are there any specialized tests that would be most helpful to the patient?

3. How would the most likely parasitic infection be acquired?

4. Diagram the general life cycle of the most likely infection.

Answer 1

1) The parasites causing urinary problems are primarily three:-

1) Schistosoma hematobium

2) Trichomonas vaginalis (history of sexual intercourse is important)

3) Enterobius vermicularis (primarily a disease of intestine causing gastrointestinal symptoms)

Therefore, the organism most likely here is Schistosoma hematobium. It is one of the most prevalent water borne parasitic diseases. (Schisto-split, soma-body).

2) For all, eosinophilia will be seen in the peripheral blood smear.

For Schistosoma hematobium, tests like biopsy obtained from cystoscope is useful and is examines microscopically. Eggs will be seen which are elongated, smooth shelled, rounded anterior end and characteristic terminal spine from the tapered posterior end will be present. Immunofluorescent antibody test, ELISA, RIA and complement fixation tests are also useful.

For Enterobius vermicularis, stool specimen is useful which yields adult worm on the surface of stool. Stool microscopy is not useful as the organism doesn't pass eggs into the faeces. NIH SWAB is useful.

For Trichomonas vaginalis, Urine specimen or prostatic secretions are taken for phase contrast microscopy. Trophozoites will be seen. Fluorescent microscopy can be done. Staining with Giemsa, Leishman, PAS stain can also be done. Culture can be done on Trusell and Johnson's medium, Simplified Trypticase serum medium. PCR, Nucleic acid amplification test can be performed.

3) Most likely organism is Schistosoma hematobium. Trichomonas is a sexually transmitted disease. Enterobius most commonly affects GIT so diarrhoea, abdominal pain, etc. should be present.

S.hematobium is generally acquired through water. Its definitive host is man and intermediate host is snail (Bulinus species).

The free living cercariae released from infected snails have the capability of directly penetrating the water softened skin of human beings bathing or wading in this water. On entering the skin the cercariae shed their tails and become schistosomulae which enter into peripheral venules. From here they are carried through the vena cava into the heart and then to systemic circulation. Then they pass through capillary bed in the intestine and through portal vein reach liver. The maturation occurs there and they migrate against the blood current into the portal system venules primarily those of the urinary bladder. In urine, their eggs are shed.

This organism is a definitive cause of urinary bladder carcinoma with an associated five fold risk.

Risk factors for Schistosoma infection are:-

1) Smoking: smoking contains some chemical irritants which chronically irritate the bladder lining predisposing to Schistosoma hematobium infection.

2) Egypt region and other Mediterranean countries. Or travel history to these regions.

4) Life cycle of Schistosoma hematobium:-