Amoebae​-75

What are amoebae?

Unicellular microorganisms

What group do amoebae belong to?

Protozoa

What are the two stages in the amoebae life cycle?

Trophozoite (actively motile feeding state) and cyst (quiescent, resistant, infective)

How do amoebae replicate?

Binary fission of trophozoite or development of trophozoites in multinucleated cysts

How do amoebae move?

Motility by pseudopod formation (ecto/endoplasm)

What is the nature of most amoebae?

Most are commensal, some opportunistic, few pathogenic

What conditions can Entamoeba histolytica cause?

Colitis, diarrhea/dysentery, liver abscess, lung abscess

What is the life cycle and pathogenesis of Entamoeba histolytica?

Ingestion of mature cysts → excystation in small intestine → trophozoites migrate to large intestine → multiply by binary fission and produce cysts; can remain noninvasive (asymptomatic), invade intestinal mucosa (intestinal disease), or spread to liver, brain, or lungs (extraintestinal disease)

What is the diagnostic and infective stage of Entamoeba histolytica?

Mature cysts are the infective stage; cysts and trophozoites in stool are the diagnostic stages.

What are the possible clinical presentations of Entamoeba histolytica infection?

Asymptomatic luminal amebiasis, invasive intestinal amebiasis (e.g., dysentery, colitis), and invasive extraintestinal amebiasis (e.g., liver abscess, peritonitis, lung or brain involvement).

What forms the first line of defense against amebic infection in the colon?

The bilayered mucus film with commensal microbiota and soluble IgA

What enzyme does Entamoeba use to degrade the mucus barrier?

Cysteine proteases

What lectin allows Entamoeba to attach to epithelial cells?

Gal/GalNAc lectin

Which cytokines are produced in the inflammatory response to amebic infection?

IL-1β, IL-6, IL-8, IFN-γ, TNF-α

Which cytokine plays a key role in amebic disease progression?

TNF-α

Which immune cells are recruited to kill amebae during infection?

Neutrophils and macrophages

What do neutrophils and macrophages release to kill amebae?

Reactive oxygen species (ROS), nitric oxide (NO), and inflammatory cytokines

What is the major source of IL-25 in the intestine?

Intestinal tuft cells

How does amebic infection affect IL-25?

It downregulates IL-25 production

What immune response does recombinant IL-25 promote?

Type 2 immune response and eosinophilia

What immune elements are associated with protection from reinfection?

Ameba-specific mucosal IgA, IFN-γ, and IL-17A from CD4+ and CD8+ T cells

What is the primary method for diagnosing amebiasis?

Microscopic ID of cysts and trophozoites in fresh or concentrated stool, aspirates, or biopsy material

What diagnostic method is used for extraintestinal abscess formation?

Imaging techniques

What immunodiagnostic tools are used in amebiasis?

Antibody and antigen detection

Why is species differentiation important in amebiasis diagnosis?

To distinguish E. histolytica from non-pathogenic amebae like E. dispar, E. coli, etc.

Which molecular methods can differentiate pathogenic from non-pathogenic amebae?

PCR or DNA probe assays

What is Entamoeba polecki?

A parasite of pigs and monkeys that can cause mild diarrhea in humans

What is the treatment for asymptomatic Entamoeba histolytica infection?

Iodoquinol, paromomycin, or diloxanide furoate

What is the treatment for symptomatic intestinal or extraintestinal Entamoeba histolytica infection?

Metronidazole or tinidazole, followed by iodoquinol or paromomycin

How can amebiasis be prevented?

Sanitation, chlorination and filtration of water, avoiding high-risk sexual practices, and travel awareness

What is a distinguishing microscopic feature of E. histolytica trophozoites?

Ingested erythrocytes stained as dark inclusions with trichrome

What nuclear features are seen in E. histolytica under microscopy?

Small, centrally located karyosome with thin, uniform peripheral chromatin

Why is ingestion of erythrocytes important in amebiasis diagnosis?

It helps differentiate E. histolytica from non-pathogenic amebae

What CNS disease is caused by Naegleria fowleri?

Meningoencephalitis

Which organisms can cause granulomatous encephalitis?

Acanthamoeba spp., Balamuthia mandrillaris

Which organisms can cause brain abscesses?

Acanthamoeba spp., Balamuthia mandrillaris

Which parasite is associated with keratitis in the eye?

Acanthamoeba spp.

What causes nodules or swellings in the skin and subcutaneous tissue?

Acanthamoeba spp.

What are the infective and diagnostic stages of Acanthamoeba spp.?

Trophozoites are infective; cysts and trophozoites are diagnostic

Where can Acanthamoeba spp. be found in the environment?

Soil, fresh/brackish/sea water, sewage, swimming pools, contact lens equipment, medicinal pools, dental units, dialysis machines, HVAC systems, vegetables, cell cultures, human tissues

How do Acanthamoeba spp. enter the human body?

Through the eye, nose, or damaged skin

What condition can Acanthamoeba cause in contact lens users?

Severe keratitis

What serious CNS condition can result from hematogenous spread of Acanthamoeba?

Granulomatous amebic encephalitis (GAE)

Who is at risk for disseminated Acanthamoeba disease?

Individuals with compromised immune systems

What stages of Acanthamoeba are found in human tissue?

Cysts and trophozoites

What are the three stages of Naegleria fowleri?

Cyst, trophozoite, and flagellated forms

How do Naegleria fowleri trophozoites replicate?

By promitosis, where the nuclear membrane remains intact

Where is Naegleria fowleri commonly found?

Fresh water, soil, thermal discharges, heated pools, hydrotherapy/medicinal pools, aquariums, and sewage

What form of Naegleria fowleri is temporary and non-feeding?

Flagellated form

What condition does Naegleria fowleri cause when trophozoites enter the brain?

Primary amebic meningoencephalitis (PAM)

Are cysts seen in brain tissue in Naegleria fowleri infection?

No, cysts are not seen in brain tissue

What is the diagnostic stage of Naegleria fowleri?

Trophozoites in cerebrospinal fluid (CSF)

What is the infective stage of Naegleria fowleri?

Trophozoite

What is the epidemiology of free-living amebic infections?

Infrequent, but occur worldwide

What disease does Naegleria fowleri cause?

Acute primary amebic meningoencephalitis (PAM)

What are the symptoms of PAM caused by Naegleria fowleri?

Severe headache, meningeal signs, fever, vomiting, altered smell, focal neurologic deficits

What is the progression of PAM?

Frequently coma and death within less than 10 days

What disease does Acanthamoeba spp. commonly cause?

Subacute or chronic granulomatous amebic encephalitis (GAE)

What are the symptoms of GAE caused by Acanthamoeba spp.?

Headaches, altered mental status, focal neurologic deficits, leading to death within several weeks

What cutaneous symptom is associated with Acanthamoeba spp.?

Granulomatous skin lesions

What ocular condition is associated with Acanthamoeba spp.?

Severe keratitis and corneal ulcers

What increases risk for Acanthamoeba keratitis?

Trauma or contact lens use with poor hygiene or contaminated water

How can amebae be cultured in the lab?

On plates with gram-negative bacteria; amebae leave trails

How is Naegleria fowleri diagnosed microscopically?

Microscopic examination of CSF; wet mount may detect motile trophozoites, Giemsa-stained smear shows typical morphology

How is Acanthamoeba spp. diagnosed microscopically?

Microscopic examination of stained smears from biopsy specimens (brain, skin, cornea) or corneal scrapings; identifies trophozoites and cysts

What advanced diagnostic methods are used for Acanthamoeba and Naegleria?

Immunofluorescent antibody detection, cultivation, and real-time PCR

What is the treatment for free-living amebic infections?

Largely ineffective; some success with amphotericin B combined with miconazole and rifampin

How can free-living amebic infections be prevented?

Prevention!