Free living Pathogenic Amoebae

Question 1

-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

Answer 1

Acanthamoeba

Question 2

Acanthamoeba is characterized by an active trophozoite stage with characteristic prominent “_________” appendages (____________)

Answer 2

Thorn-Like appendages ACANTHOPODIA

Question 3

_____ ______ feed on gram-negative bacteria, blue-green algae, or yeasts and reproduce by binary fission

Answer 3

Motile Trophozoites

Question 4

• 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

Answer 4

Acanthamoeba Trophozoites

Question 5

Acanthamoeba has only two stages, _____ and _____, in its life cycle

Answer 5

Cyst and Trophozoites

Question 6

No flagellated stage exists as part of the life cycle

Answer 6

Fact

Question 7

The Acanthamoeba trophozoites replicates by _____?

Answer 7

Mitosis

Question 8

What is the infective stage of Acanthamoeba

Answer 8

Trophozoite stage

Question 9

both cysts and trophozoites gain entry into the body through various means. Entry can occur through the _____, the ______ to the ______, or ______ or _______

Answer 9

eye, the nasal passages to the lower respiratory tract, or ulcerated or broken skin

Question 10

Acanthamoeba spp. have been implicated as possible reservoir hosts for medically important bacteria such as ______ spp., _____, and gram-_____ _____ (such as E. coli).

Answer 10

Legionella spp., mycobacteria, and gram-negative bacilli

Question 11

Acanthamoeba was first described as an opportunistic ocular surface pathogen causing _____ ______

Answer 11

Keritis in 1974

Question 12

associated with the use of improperly disinfected soft contact lenses, particularly those which are rinsed with tap water or contaminated lens solution

Answer 12

Acanthamoeba keritis

Question 13

An immunocompromised state contributes to increased susceptibility to infection, and may lead to disseminated disease in the lungs and brain (GAE).

Answer 13

Fact

Question 14

Symptoms of AK

Answer 14

• 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.

Question 15

Progression of infection may cause?

Answer 15

• scleritis and iritis, and

-may ultimately lead to vision loss

Question 16

Major differentials which need to be ruled out include?

Answer 16

fungal and herpetic keratitis

Question 17

Acanthamoeba keratitis is diagnosed by epithelial biopsy or corneal scrapings for recoverable ameba with characteristic staining patterns on histologic analysis.

Answer 17

Fact

Question 18

Species-specific identification can be made from culture and molecular analysis through PCR.

Answer 18

Fact

Question 19

Known species that have caused AK include?

Answer 19

• A. castellani,
• A. culbertsoni,
• A. hutchetti,
• A. polyphaga, and
• A. rhysoides.

Question 20

causative agent of human GAE by Stamm in 1972.

Answer 20

Acanthamoeba

Question 21

Amebae were demonstrated in brain
sections of a GAE patient using indirect fluorescence microscopy

Answer 21

Fact

Question 22

usually occurs in immunocompromised hosts including the:

-chronically ill and debilitated, and

-those on immunosuppressive agents such as chemotherapy and

-anti-rejection medications

Answer 22

Glaucomatous Amebic Encephalitis

Question 23

Signs and symptoms of GAE are generally related to the:

Answer 23

• destruction of brain tissue and the
• associated meningeal irritation

Question 24

Systemic manifestations early in the course include:

Answer 24

-fever,

-malaise, and

-anorexia.

Question 25

Neurologic findings depending on the location of the lesions include

Answer 25

• hemiparesis,
• blurring of vision,
• diplopia,
• cranial nerve deficits,
• ataxia, and
• increased intracranial pressure

Question 26

From a primary site of infection in the skin or lungs, the likely route of invasion is ______.

Answer 26

Hematogenous (carried by blood)

Question 27

The incubation period from initial inoculation is approximately ____ days

Answer 27

10

Question 28

The natural course of the GAE disease eventually results in coma and death

Answer 28

Fact

Question 29

Diagnosis of GAE is usually made _____-_____ in most cases

Answer 29

post-mortem

Question 30

Medical Treatment for AK

Answer 30

• 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.

Question 31

D’Aversa & Colleagues for the treatment of Acanthamoeba

Answer 31

clotrimazole combined with pentamidine, isethionate, and neosporin.

Question 32

Topical corticosteroids should be avoided, as this retards the immune response.

Answer 32

Fact

Question 33

Advanced AK usually requires debridement, but complete excision of the cornea can be avoided if the infection is confined to more superficial areas

Answer 33

Deep lamellar keratectomy

Question 34

GAE usually heralds a fatal outcome within __ to ___ days

Answer 34

3-40

Question 35

first to diagnosed Acanthamoeba GAE in a living patient in 1991.

Answer 35

De Jockheere

Question 36

The first case of AK was recognized in the Philippines in the 1990s from a patient from the Philippine General Hospital,

Answer 36

Fact

Question 37

• are free-living protozoans
• with two vegetative forms:
  an ameba (trophozoite form), and
  a flagellate (swimming form).

Answer 37

Naegleria spp.

Question 38

A _____ cyst form is produced when conditions are not favorable

Answer 38

Dormant (inactive)

Question 39

Transformation from the trophozoite to the flagellate form may facilitate more rapid movement toward food sources.

Answer 39

Fact

Question 40

There are two forms of trophozoites of Naegleria fowleri:

Answer 40

-ameboid and

• ameboflagellate

Question 41

Naegleria fowleri has three stages,
- _____,
- _____,
- and _____, in its life cycle.

Answer 41

• cysts,
• trophozoites,
• and flagellated forms

Question 42

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.

Answer 42

Promitosis

Question 43

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.

Answer 43

Fact

Question 44

The cytoplasm is granular and contains many vacuoles.
• The single nucleus is large and has a large, dense karyosome and lacks peripheral chromatin.

Answer 44

Naegleria spp.

Question 45

Naegleria spp. are _____ organisms which thrive best in hot springs and other warm aquatic environments

Answer 45

Thermophilic

Question 46

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

Answer 46

Naegleria Fowleri

Question 47

N. fowleri trophozoites are found in cerebrospinal fluid (CSF) and tissue,

Answer 47

Fact

Question 48

flagellated forms are occasionally found in CSF.

Cysts are not seen in brain tissue

Answer 48

Fact

Question 49

N. fowleri is the causative agent of a rare but rapidly destructive and fatal meningoencephalitis termed primary amebic meningoencephalitis (PAM)

Answer 49

Fact

Question 50

usually occurs in previously healthy adults with a history of swimming

Answer 50

Primary amebic meningoencephalitis