Some pathogenic parasitesSome pathogenic parasites

• 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 amoebic meningoencephalitis.

• 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, con

gestion 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 affected areas.

• 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 response.

• 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 prevention.

• Acanthamoeba castellani, A.culberstoni and A.astronyxis cause opportunistic granulomatous amoebic encephalitis (GAE), and opportunistic infection of lungs and skin in the immunocompromised.

• 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 skin.

• The trophozoite reach the lower respiratory tract, particularly the lungs.They multiply by binary fission.

• 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 congested conjunctiva.

• 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 occasionally.

• 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 pathogenic diarrhea.

• 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 ileum.

• 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 feces.

• Life cycle and transmission:

• The life cycle of B.coli has two stages that of a trophozoite and the cyst.

• 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 lumen parasites.

• 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 additional symptoms.

• 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 route.

• 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 diseases caused.

• 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 immunocompromised individuals.

• Rarely, can cause pulmonary infections or infect the bile ducts to cause cholecystitis and cholangitis.

• 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, watery diarrhea.

• 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 m

ade by microscopic examination for spherical oocysts in a modified acid-fast staining of fecal sample.

• Treatment of choice: Trimethoprim-sulfamethoxazole.