Free living Pathogenic Amoebae Flashcards
-is a ubiquitous
-free-living ameba
-etiologic agent of Acanthamoeba keratitis (AK) and granulomatous amebic encephalitis (GAE)
- a highly resilient cyst stage into which it transforms when environmental conditions are not favorable
- It is an aquatic organism that is found in a myriad of natural and artificial environments and can survive even in contact lens cleaning solutions.
- can also adapt to feed on corneal epithelial cells and neurologic tissue through phagocytosis and secretion of lytic enzymes
Acanthamoeba
Acanthamoeba is characterized by an active trophozoite stage with characteristic prominent “_________” appendages (____________)
Thorn-Like appendages ACANTHOPODIA
_____ ______ feed on gram-negative bacteria, blue-green algae, or yeasts and reproduce by binary fission
Motile Trophozoites
- single large nucleus with a centrally-located
- densely staining nucleolus; a large endosome
- finely granulated cytoplasm
- and a large contractile vacuole.
- Small, spiny filaments for locomotion known as acanthapodia are evident on phase-contrast microscopy
Acanthamoeba Trophozoites
Acanthamoeba has only two stages, _____ and _____, in its life cycle
Cyst and Trophozoites
No flagellated stage exists as part of the life cycle
Fact
The Acanthamoeba trophozoites replicates by _____?
Mitosis
What is the infective stage of Acanthamoeba
Trophozoite stage
both cysts and trophozoites gain entry into the body through various means. Entry can occur through the _____, the ______ to the ______, or ______ or _______
eye, the nasal passages to the lower respiratory tract, or ulcerated or broken skin
Acanthamoeba spp. have been implicated as possible reservoir hosts for medically important bacteria such as ______ spp., _____, and gram-_____ _____ (such as E. coli).
Legionella spp., mycobacteria, and gram-negative bacilli
Acanthamoeba was first described as an opportunistic ocular surface pathogen causing _____ ______
Keritis in 1974
associated with the use of improperly disinfected soft contact lenses, particularly those which are rinsed with tap water or contaminated lens solution
Acanthamoeba keritis
An immunocompromised state contributes to increased susceptibility to infection, and may lead to disseminated disease in the lungs and brain (GAE).
Fact
Symptoms of AK
- severe ocular pain and blurring of vision.
- Corneal ulceration with progressive corneal infiltration may occur.
- Primary amebic infection or secondary bacterial infection may lead to hypopyon formation.
Progression of infection may cause?
- scleritis and iritis, and
-may ultimately lead to vision loss
Major differentials which need to be ruled out include?
fungal and herpetic keratitis
Acanthamoeba keratitis is diagnosed by epithelial biopsy or corneal scrapings for recoverable ameba with characteristic staining patterns on histologic analysis.
Fact
Species-specific identification can be made from culture and molecular analysis through PCR.
Fact
Known species that have caused AK include?
- A. castellani,
- A. culbertsoni,
- A. hutchetti,
- A. polyphaga, and
- A. rhysoides.
causative agent of human GAE by Stamm in 1972.
Acanthamoeba
Amebae were demonstrated in brain
sections of a GAE patient using indirect fluorescence microscopy
Fact
usually occurs in immunocompromised hosts including the:
-chronically ill and debilitated, and
-those on immunosuppressive agents such as chemotherapy and
-anti-rejection medications
Glaucomatous Amebic Encephalitis
Signs and symptoms of GAE are generally related to the:
- destruction of brain tissue and the
- associated meningeal irritation
Systemic manifestations early in the course include:
-fever,
-malaise, and
-anorexia.
Neurologic findings depending on the location of the lesions include
- hemiparesis,
- blurring of vision,
- diplopia,
- cranial nerve deficits,
- ataxia, and
- increased intracranial pressure
From a primary site of infection in the skin or lungs, the likely route of invasion is ______.
Hematogenous (carried by blood)
The incubation period from initial inoculation is approximately ____ days
10
The natural course of the GAE disease eventually results in coma and death
Fact
Diagnosis of GAE is usually made _____-_____ in most cases
post-mortem
Medical Treatment for AK
- only surgical excision of the infected cornea with subsequent corneal
transplantation was curative - aggressive combination anti-amebic agents can preclude the need for extensive surgery.
- amphotericin B, pentamidine isethionate, sulfadiazine, flucytosine, fluconazole or itraconazole.
D’Aversa & Colleagues for the treatment of Acanthamoeba
clotrimazole combined with pentamidine, isethionate, and neosporin.
Topical corticosteroids should be avoided, as this retards the immune response.
Fact
Advanced AK usually requires debridement, but complete excision of the cornea can be avoided if the infection is confined to more superficial areas
Deep lamellar keratectomy
GAE usually heralds a fatal outcome within __ to ___ days
3-40
first to diagnosed Acanthamoeba GAE in a living patient in 1991.
De Jockheere
The first case of AK was recognized in the Philippines in the 1990s from a patient from the Philippine General Hospital,
Fact
- are free-living protozoans
- with two vegetative forms:
an ameba (trophozoite form), and
a flagellate (swimming form).
Naegleria spp.
A _____ cyst form is produced when conditions are not favorable
Dormant (inactive)
Transformation from the trophozoite to the flagellate form may facilitate more rapid movement toward food sources.
Fact
There are two forms of trophozoites of Naegleria fowleri:
-ameboid and
- ameboflagellate
Naegleria fowleri has three stages,
- _____,
- _____,
- and _____, in its life cycle.
- cysts,
- trophozoites,
- and flagellated forms
The trophozoites replicates by _____ (nuclear membrane remains intact) and can turn into temporary non-feeding flagellated forms, which usually revert back to the trophozoite stage.
Promitosis
Trophozoites infect humans or animals 10 to 35 µm but when rounded are usually 10 to 15 µm in diameter. In culture,
•trophozoites may get over 40 µm.
Fact
The cytoplasm is granular and contains many vacuoles.
• The single nucleus is large and has a large, dense karyosome and lacks peripheral chromatin.
Naegleria spp.
Naegleria spp. are _____ organisms which thrive best in hot springs and other warm aquatic environments
Thermophilic
Only _____ _____ has been reported to consistently cause disease in humans, although some non-fowleri species may cause opportunistic infections
able to survive in elevated
temperatures and reproduces rapidly in temperatures above 30°C
Naegleria Fowleri
N. fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue,
Fact
flagellated forms are occasionally found in CSF.
Cysts are not seen in brain tissue
Fact
N. fowleri is the causative agent of a rare but rapidly destructive and fatal meningoencephalitis termed primary amebic meningoencephalitis (PAM)
Fact
usually occurs in previously healthy adults with a history of swimming
Primary amebic meningoencephalitis
