• Primary amoebic meningoencephalitis (PAM) is
comparatively rare but a serious disease caused
by free-living amebas belonging to genus
Naegleria and Acanthamoeba.
• Naegleria spp affect children and young adults
and acquired by swimming in fresh water and is
almost always fatal.
• Acanthamoeba spp are found in soil and in fresh
and brackish water.
• N.fowleri is the main causative agent of primary
• Its life cycle includes amoeboid trophozoites, a
temporary flagellar stage known as
amoebaflagellate and cysts, with rapid
transformation from one form to another.
• N.fowleri is found as amoeboid trophozoite and
amoebaflagellates. They usually enter the body
through mucous membranes and penetrate the
nasal mucosa and cribriform plate.
• The trophozoites are neutrophic and produce a
purulent meningitis and encephalitis.
Pathogenesis and clinical findings:
The incubation period of PAM ranges from 2-15 days.
The trophozoites invade the CNS resulting in cerebral oedema,
congestion of leptomeningeal vessels and acute rhinitis and are
characteristic of PAM.
The cerebral hemisphere is congested, hemorhagic, purulent and
necrotic. The olfactory mucosa and olfactory bulbs are the most
The infection is also characterized by rapid onset of severe bifrontal
headache, seizures and at times, abnormalities in taste and smell.
The condition progressively worsens into coma resultin in death
within a few days.
• Lab diagnosis includes examination of
cerebrospinal fluid that is usually bloody
and demonstrates an intense neutrophilic
• The protein levels are elevated and
glucose levels are decreased.
• Early microscopic examination of CSF
reveals typical trophozoites.
• Treatment and Prevention:
• To date, only four cases have survived a
Naegleria infection. All were diagnosed
early and treated with high-dose of
Amohotericin B along with Rifampin.
• Avoiding contact with stagnant and
thermal water/swimming pools is the only
• Acanthamoeba castellani, A.culberstoni and
A.astronyxis cause opportunistic granulomatous
amoebic encephalitis (GAE), and opportunistic
infection of lungs and skin in the
• They cause acanthamoebic keratitis in healthy
individuals.Transmission is through the
inhalation of aerosol or dust containing cysts and
trophozoite or through direct invasion of broken
• The trophozoite reach the lower respiratory tract,
particularly the lungs.They multiply by binary
• They have only two stages in their life cycle: the
trophozoite and the cyst and both can be found
in human infections.
• Acanthamoeba infections occur more frequently
in debilitated and chronically ill individuals and
reach the CNS by hematogenous dissemination
from foci in the lung, skin or the sinuses.
• Pathogenesis and clinical findings:
• Histoliogically, Acanthamoeba infections produce a
diffuse, necrotizing, granulomatous amoebic encephalitis
(GAE), with frequent involvement of the mid-brain. Both
cysts and trophozoites are seen in lesions.
• Unlike PAM, GAE shows an insidious onset of symptoms
with focal neurological symptoms.
• Mental abnormalities, seizures, fever, hemiparesis,
headache, meningism and visual abnormalities.
• The disease worsens within a week to several weeks
resulting in coma and death. The disease in
immunocompromised is invariably fatal.
• Acanthamoeba keratitis in healthy adults is
associated with use of contaminated contact
lens (with contaminated lens disinfectant and tap
water). It is a chronic, progressive and ulcerative
disease of the eye.
• Ulcers in the cornea are painful and the cornea
shows a characteristic annular infiltration and
• If treatment unsuccessful, the disease
progresses to corneal perforations resulting in
blindness and corneal prolapse.
• Laboratory diagnosis:
• Microscopic examination of biopsy
specimens of CSF reveal trophozoite
• Demonstration of double-walled
trophozoite amoeba in Giemsa stained
corneal scrapings stained and wet mount
shows motile trophozoites.
• Treatment and prevention:
• No effective therapy is available for GAE.
• Acanthamoeba infections, especially new cases,
can be treated with Pentamidine, Ketoconazole
or flucytosine. Established infections appear to
respond to Amphotericin B.
• Prevention of Acanthamoeba keratitis is by
avoiding contaminated disinfectants and use of
home made disinfectants for the contact lens.
• Balantidium coli is the only ciliated protozoan causing
• B.coli is the largest intestinal protozoan in human body,
which resides in the large intestine, chiefly in the cecal
and sigmoidocolic regions and rarely in the terminal
• They primarily reside in the lumen, but can penetrate the
mucosa, submucosa and even the muscular layers
causing ulcers and Balantidium dysentry.
• Domestic animals, especially pigs are the main reservoir,
and humans are infected by ingesting the cysts present
in food and water contaminated with animal or human
Life cycle and transmission:
The life cycle of B.coli has two stages that of a trophozoite and the
Food and water contaminated with B. cysts are transported to the
small intestine, where their walls are broken by digestive juices and
the mobile trophozoites released.
The trophozoites reside in the lumen, multiply by binary fission and
feed on cell debris of intestinal wall, starch grains and mucous as
Alternatively, they invade the lining of the large intestine, destroying
intestinal tissue causing ulcers or abscesses.
Trophozoites, eventually form new cysts that are excreted, and
under favorable conditions begin a new cycle of growth.
Pathogenesis and clinical findings:
B.coli infections are apparently harmless, but occasionally, the trophozoites invade
the large intestinal mucosa and submucosa, producing flask shaped ulcers in the wall
of the colon, similar to the ulcers caused by E.histilytica, but unlike them, do not
cause any extra-intestinal lesions.
The abscesses are small and when incised are filled with a mucoid material infiltrated
with round-cell lymphocytes, eosinophils and polymorpho leukocytes and containing
numerous Balantidia collected in nests within the tissues.
B.coli infections can be asymptomatic, chronic with recurrent diarrhea (most
common) or acute dysentric infection.
Chronic recurrent diarrhea ( accompanied by bloody mucoid stools, tenesmus,
anorexia, nausea, epigastric pain and vomiting) alternating with constipation is the
most common clinical finding.
Severe cases may resemble severe intestinal amebiasis with >10 stools per day and
may be fatal.
Loss of appetite, headache, insomnia, muscular weakness and loss in weight are
• Laboratory diagnosis includes finding large
ciliated trophozoites or large cysts with a
characteristic V-shaped nucleus, in the stool.
• Treatment of choice is Tetracycline.
Metronidazole can also be used.
• Prevention by avoiding food and water
contaminated with domestic animal feces.
• Microsporidia are a group of protozoa characterized by
obligate intracellular replication and spore formation.
• Of the 14 species of Microsporidia currently known to
infect humans, Enterocytozoan bieneusi and
Encephalitozoan intestinalis are the most common
causes, associated with diarrhea and systemic disease.
• The mature and infectious spores of the microsporidia
spp infect humans.
• A characteristic feature of the spore is a ‘polar tube’
(through which the protoplasm enters the cell) coiled
within the spore and extrudes to attach to the epithelial
cells upon infection.
• Human to human transmission is mainly by the fecal-oral
• Pathogenesis and clinical findings:
• Microsporidia have emerged as causes of
infectious diseases in immunocompromised
individuals.This is due to improved diagnostic
methods and increased awareness of the
• Microsporidia also implicated in infections of the
CNS, the genitourinary tract and the eye.
• Enterocytozoan bieneusi infections result
through ingestion of spores with the primary site
of infection being the enterocytes lining the
duodenum and jejunum of the small intestine.
• Clinical manifestations include persistent
diarrhea, abdominal pain and weight loss in
• Rarely, can cause pulmonary infections or infect
the bile ducts to cause cholecystitis and
• Health individuals can get self limiting diarhea of
upto one months duration.
• Encephalitozoan intestinalis infections is through
ingestion or inhalation of spores with primary
infection in the enterocytes of the small intestine
or respiratory tracts.
• Sexual transmission also likely as found in the
urethra and prostate of several AIDS patients.
• Immunocompromised develop persistent
diarrhea. Unlike, Enterocytozoan bieneusi,
Encephalitozoan intestinalis can disseminate
and cause sinusitis, keratoconjunctivitis,
encephalitis, tracheobronchitis, interstitial
nephritis, hepatitis or myositis.
• Laboratory diagnosis includes:
• Serological methods such as Immunofluoroscent
antibody staining, ELISA and Western blot assay.
• Definitive diagnosis by detecting microsporidia in urine,
stool, tissue biopsies, stained by specific stains for
different specimens like trichrome for stool specimen,
silver stain in tissue biopsies etc…
• PCR increasingly used for detection.
• Treatment of choice: Albendazole.
Isospora belli causes intestinal coccidiosis, rarely in humans.
Parasite is acquired by transmission of oocysts from either human
or animal sources, by the fecal-oral route.
The oocyst excyst in the upper small intestine and invade the
mucosa, causing destruction of the brush border. This results in
various gastrointestinal upsets, including nausea, pain and chronic
diarrhea, and may last for months to years.
Immunocompromised individuals present with chronic, profuse,
Lab diagnosis by finding typical oocysts in stool sample.
Treatment of choice: Trimethoprim-sulfamethoxazole.
• Cyclospora cayetanensis is an intestinal protozoan.
• Causes watery diarrhea in both the
immunocompromised (diarrhea can be prolonged and
relapsing) and the immunocompetent.
• Transmitted through fecal-oral route.
• Also a Coccidia (subclass of sporozoa) and diagnosis
made by microscopic examination for spherical oocysts
in a modified acid-fast staining of fecal sample.
• Treatment of choice: Trimethoprim-sulfamethoxazole.