Single Case Reports
A Case of Encephalitozoon cuniculi Peritonitis
in a Patient with AIDS
HERVE O. ZENDER, M.D., EVIANO ARRIGONI, M.D., JOHANNES ECKERT, M.D., AND YUSUF KAPANCI, M.D.
A 45-year-old man with acquired immune deficiency syndrome
(AIDS) presented with an unusual peritonitis resulting from a
microsporidian infection. An inflammatory mass formed by the
omentum magnum was revealed at partial autopsy. This mass
was infested with parasites measuring 2.5-2.6 /tin by 1.2-1.5
jun, which appeared gram positive and stained dark blue with
Giemsa stain. These organisms were pale pink with Kinyoun
stain, and occasionally one of their poles was periodic acid-Schiff
positive. Sporoblasts and spores contained in parasitophorous
vacuoles were revealed by electron microscopic examination.
These spores were mononucleated, without mitochondria, and
had a polar filament with four or five coils. They were identified
as Encephalitozoon cuniculi. Peritonitis resulting from this parasite has not been reported previously, however, it should be
suspected among rare infections resulting from unusual parasites
in patients with AIDS. (Key words: Encephalitozoon cuniculi;
Microsporidiosis; AIDS; Peritonitis) Am J Clin Pathol 1989;92:
352-356
ENCEPHALITOZOON
CUNICULI is a protozoan parasite; it belongs to the phylum Microspora (class: Microsporea; order: Microsporida; suborder: Apansporoblastina)6,7 and was first described by Wright and Craighead in the brain and kidney of rabbits in 192222; Levaditi
and colleagues coined its name in 1923.12 In 1964, however, this name Encephalitozoon was dropped because it
was believed that Nosema was the same parasite. I0 Eventually, in 1971 ultrastructural differences were observed
between the two parasites; consequently the genus Encephalitozoon was resurrected.19
E. cuniculi has an obligatory intracellular development
in macrophages, vascular and perithelial cells, and kidney
tubular cells.17 It is a common parasite of domesticated
and wild rabbits and other laboratory rodents.21 As much
as 20 to 50% of these are latently infected with E. cuniculi,
resulting in chronic symptoms. 18 However, it may also
infect a wide spectrum of other mammals, such as dogs,
Received October 6, 1988; received revised manuscript and accepted
for publication December 21, 1988.
Address reprint requests to Dr. Kapanci: Institut de Pathologie clinique,
Centre Medical Universitaire, CH-1211 Geneva 4, Switzerland.
Departments of Pathology and Medicine, University of
Geneva, Geneva, and Institute of Parasitology,
University of Zurich, Zurich, Switzerland
cats, foxes, leopards, guinea pigs, shrews, goats, swine,
horses, monkeys, and humans. Encephalitozoon-like organisms have also been found in birds, but species identification is unclear.4
The life cycle of E. cuniculi lasts three to five days,
merogonic then sporogonic, within an intracellular parasitophorous vacuole; the sporogony is disporous with no
pansporoblastic membrane; the spore is monokaryotic.
Its length and width are 2.5 and 1.5 /im, respectively. It
has no mitochondria and its ribosomes resemble those of
bacteria; the exosporous and endosporous walls are thick.
The parasite contains an extrusion apparatus: a polar filament consisting of five to six tubular coils fixed to a
polaroplast.17,21
The first human infection with E. cuniculi was reported
in 1959,14 and a few other cases have been reported since
then.2-4-9-20
Other microsporidia can infect humans: Nosema connori,13 Pleistophora," and Enterocytozoon bieneusi.*']5,n
Two cases of corneal microsporidoses were ascribed to
Microsporidium ceylonensis and Microsporidium africanum, respectively.1'4'6
We report here the first description of a human peritonitis secondary to E. cuniculi in a patient with acquired
immune deficiency syndrome (AIDS).
Report of a Case
A 45-year-old man was admitted to the hospital in November 1987,
complaining of weakness, progressive dyspnea, and fever with thrills.
During the last year, he had lost 13 kg. Anamnesis revealed no former
particular disease. The patient claimed that he was not a drug addict nor
a homosexual, even occasionally. However, he had had contact with
prostitutes several times.
Clinical and laboratory observations led to the diagnosis of AIDS at
stage IV CI according to the Centers for Disease Control (CDC) classi-
352
Vol. 92 • No. 3
SINGLE CASE REPORTS
353
FIG. 1 (upper). Omentum magnum; mixed inflammation and nests of microorganisms. Hematoxylin and eosin (X250).
FIG. 2 (lower, left). Nest of microorganisms. Giemsa (X400).
FIG. 3 (lower, left center). Nest of microorganisms. Gram (X400).
FIG. 4 (lower, right center). Nest of microorganisms irregularly stained with periodic acid-SchifF. Periodic acid-Schiff (X400).
FIG. 5 (lower, right). Nest of microorganisms very lightly stained with Kinyoun stain. Kinyoun (X400).
fication.5 The patient presented with oral candidasis, bilateral Pneumocystis carinii pneumonia, and associated cytomegalovirus (CMV) infection. Pneumonic infections were confirmed by bronchoalveolar lavage.
The T-lymphocytic ratio CD4/CD8 was 0.23 with a significant decrease
in the absolute number of CD4 T-lymphocytes (57/JIL). The urine was
normal. The erythrocyte sedimentation rate was 75 mm (first hour); the
hematocrit was 32%, the white blood cell count was 7,100 with 74%
neutrophils, 25% lymphocytes, and 3% monocytes. The glucose was 6.6
mmol/L, sodium 137 mmol/L, potassium 4.2 mmol/L, urea nitrogen
5.5 mmol/L, creatinine 103 jimol/L, total bilirubin 8 ^mol/L, alkaline
phosphatase 82 U, aspartate aminotransferse (AST) 83 U, and alanine
aminotransferase (ALT) 41 U/L. A treatment including amphotericin
B topically and trimethoprim-sulfamethoxazole was started.
However, 48 hours later, the patient became bradypsychic; cerebral
atrophy was objectivated on computed axial tomography (CAT) scan
images. Clinical and paraclinical investigations revealed an acute renal
failure. In the abdomen a large palpable mass suggesting a tumor was
found; it occupied predominantly the right hypochondrus. This mass
was slightly painful at palpation, but there was no peritonismus, and no
intestinal abnormalities were seen on CAT scan images.
The evolution was characterized by the development of a subileus
associated with fever that did not respond to broad-spectrum antibiotic
therapy. Because of the rapid progression of the disease, in agreement
with the family's wishes, it was decided that surgery would not be performed. Instead, the patient's comfort was assured. He died 40 days after
admission to the hospital for a P. carinii pneumonia.
AJ.C.P. • September 1989
ZENDER ET AL.
354
~^T
it A (X w "
^TT~^F^r*7
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Vk
i'^
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FlG. 6. Sporoblasts and spores within an intracellular parasitophorous vacuole. Sb = sporoblast;
Sp/ = young spore; Sp2 = mature spore. Electron microscopy (X6,000).
FIG. 7 (inset). Spore with cross-section of a polarfilamentwith four coils (arrows). En = endospore; Ex = exospore. Electron microscopy (X39,000).
Autopsy
Full autopsy was refused by the family. Accordingly,
we took only a few tissue samples through a small laparotomy three hours after death.
The abdomen contained 3 L of yellow, cloudy, and
fibrinous ascitic fluid. The mass occupying the right hypochondrus corresponded in fact to the omentum magnum, which was thickened and firm, appearing as an irregular lobulated mass; it measured about 20 X 20 X 10
cm. There were no liver lesions, and the spleen was firm
and enlarged (17 cm in length). No gastrointestinal perforations were observed.
The omentum magnum, liver, spleen, and ascitic fluid
were investigated with light and electron microscopy; the
ascitic fluid was put under culture. Tissues for routine
histologic study werefixedin 10% formaldehyde, and sections were stained with hematoxylin and Eosin, Giemsa,
Gram's, Ziehl-Neelsen, Kinyoun, and periodic Acid-Schiff
stains. The tissue samples, for electron microscopic examination, were fixed in 2% cacodylate buffered glutaraldehyde, postfixed in osmium, embedded in epoxy, cut
with a Reichert Ultratome®, and investigated with the use
of a Philips 400® electron microscope.
Histologic examination of the omentum magnum revealed a mixed nongranulomatous inflammation with
some epitheloid cells and spots of necrosis. Oval microorganisms (2.5-2.6 fim by 1.2-1.5 /*m) with dark nuclei
were dispersed as nests, within the extracellular space.
These organisms appeared gram positive; they stained pale
basophilic with hematoxylin and eosin, dark blue with
Giemsa, and pale pink with Kinyoun stains. However,
common stains for acid-fast bacteria such as Ziehl-Neelsen
did not stain these microorganisms. They were occasionally positively stained at one pole with periodic acid-Schiff
and were indeed especially distinct with the Giemsa and
Gram's stains (Figs. 1 to 5).
Electron microscopic examination revealed sporoblasts
and spores in an intracellular parasitophorous vacuole.
The spores were devoid of mitochondria; they contained
a single nucleus, sometimes a vacuole, and, at the periphery, cross-section of a polar filament with four to five
coils. The spores were enclosed with both a thin-pleated
exosporous and thick endosporous wall (Figs. 6-9).
Histologic examination of the ascitic fluid revealed
many neutrophils and gram-negative rods that did not
grow on culture. Some steatosis was present in the liver,
with moderate cholestasis and no inflammation. In the
Vol. 92 • No. 3
SINGLE CASE REPORTS
355
/.;!%--f^Jjf1
-,
Ex-
ts<;:
•.<MBP*
FIG. 8. Spores with a single nucleus (A1), a coiled polar filament (arrows), and sometimes a vacuole (V).
En = endospore; Ex = exospore. Electron microscopy (X42.000).
FIG. 9 (inset). Cross-section of a spore with a thick endosporous (En) and a pleated exosporous (Ex) wall
and with a polar filament with four to five coils (arrows). Electron microscopy (X25,000).
spleen, the white pulp was atrophic and the red pulp fibrotic.
Discussion
The diagnosis of an infection by a microsporidian parasite was based on the differential stainings (basophilic
with hematoxylin and eosin, blue with Giemsa, gram positive, variably acid-fast, occasionally positive with periodic
acid-Schiff at one pole corresponding to the polar granule).3 Diagnosis was confirmed, under the electron microscope, by the observation of a polar filament with four
to five coils. 418 The species determination, E. cuniculi,
was founded on the ultrastructure: a single nucleus per
spore (two in Nosema); spore size of 1.5-2.5 nm (Nosema
and Pleistophora are much larger); the presence of an intracellular parasitophorous vacuole (absent in Nosema,
Pleistophora, and Enterocytozoon); and a polar filament
with only 4-5 coils (11 coils in Nosema, 11-13 coils in
M. africanum).4-'6-11-2'
To our knowledge, until now only the following infections with Microsporidia have been reported in humans:
one disseminated infection with N. connori in a four^
month-old immunodeficient boy in Washington, who had
hypoplasia of the thymus 13 ; two cases of keratitis with
unilateral blindness, the first resulting from M. ceylonensis
in a 11-year-old Tamil boy1 and the second from M. africanum in a 26-year-old black woman in Botswana,16
both immunologically noncompromised. Among patients
with AIDS, a Pleistophora myositis was described in a
20-year-old black man acknowledging only one homosexual contact"; severe secretory diarrheas are reported,
with variable evolutions, and invasion of the enterocytes
with E. bieneusi among Europeans, Africans, and Americans (ten cases8'15'17). E. cuniculi encephalitis had a favorable outcome in two cases: a nine-year-old Japanese
boy14 and a two-year-old Columbian boy,2 both immunologically noncompromised. E. cuniculi infection resulted in a granulomatous hepatitis in a 35-year-old homosexual man with AIDS.20 In Sweden and Great Britain,
ZENDER ET AL.
356
high prevalences of serum antibodies against E. cuniculi
were found in patients with schistosomiasis, malaria, and
neurologic disorders and among those who lived in tropical areas.2,9
The patient with AIDS described in this article had the
first reported case of a peritonitis secondary to E. cuniculi.
The partial autopsy did not allow us to uncover the
pathogenesis of this peritonitis.
As also pointed out by others,17'20 we probably will meet
more and more patients with AIDS with an associated
microsporidiosis; therefore, we will have to consider and
forsee this "new" opportunistic infection in the proteiform
AIDS syndrome.
10.
Acknowledgments. The authors thank the following for their valuable
technical assistance: Chantal Briottet, Tri Le Minh, Genevieve Leyvraz,
Marie-Claire Peclet, and Joan Stalder.
14.
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