Amoebiasis

Introduction

• Amoebiasis is responsible for approximately 100,000 deaths per year

• Mainly in Central and South America, Africa, and India

• Manifested as invasive intestinal or extraintestinal clinical features

• The third most common cause of death due to parasitic infection after malaria and schistosomiasis

Introduction cont…

• Amoebiasis is characterised by moderately expressed intoxication

• Becoming complicated in some cases abscesses of a liver, a brain, easy and other organs

• Risk groups include male homosexuals, travellers and recent immigrants and institutionalized populations.

Characteristics of Amoeba STRUCTURE characteristics: nucleus, nuclear membrane, cell

wall, vacuole, cytoplasm,endoplasm, ectoplasm

1. FEEDING: the pseudopodia engulf the food

2. MOVEMENT: the cell is pulled forward by the extended pseudopodia

3. REPRODUCTION: cell multiplies by binary MOVEMENT fission

Amoeba species

• Entamoeba histolytica• Entamoeba dispar• Entamoeba coli• Entamoeba polecki• Entamoeba hartmanni• Endolimax nana• Iodamoeba buetschlii

Entamoeba histolytica/dispar• Trophozoites of Entamoeba histolytica/dispar

similar• Without erythrophagocytosis, pathogenic

E.histolytica is morphologically indistinguishable to nonpathogenic E. dispar

• Each trophozoite has a single nucleus and a centrally placed karyosome and uniformly distributed peripheral chromatin

• Entamoeba histolytica/dispar trophozoites measure usually 15 to 20 µm (range 10 to 60 µm), tending to be more elongated in diarrheal stool

Entamoeba histolytica/dispar

• Erythrophagocytosis is the only characteristic that can be used to differentiate morphologically E. histolytica from the nonpathogenic E. Dispar

• Mature cysts have 4 nuclei• E. moshkovskii can colonize humans and is also

identical in appearance to E. histolytica/E. dispar

E. histolytica/dispartrophozoite E. histolytica with

ingested RBC

E. histolytica cyst

Entamoeba coli

• The trophozoites have one nucleus with characteristically a large, eccentric karyosome

• The cytoplasm is coarse and vacuolated• Occasionally the cytoplasm contains ingested

bacteria, yeasts or other materials• The trophozoites measure usually 20 to 25 µm,

but they can be elongated and reach up to 50 µm• Mature cysts typically have 8 nuclei, and measure

usually 15 to 25 µm (range 10 to 35 µm)• Chromatoid bodies are seen less frequently than

in E. histolytica.

E. coli trophozoite E. coli cyst

Entamoeba hartmanni• Often called a "small histolytica" because it has many

morphological characteristics, except its size• Trophozoites have one nucleus with fine peripheral

chromatin and a small centrally located karyosome• Trophozoites of E. hartmanni measure 8 to 10 µm

(range 5 to 12 µm ) and are smaller than E. histolytica• Cysts of E. hartmanni when mature have 4 nuclei and

elongated chromatoid bodies with rounded ends• Cysts of E. hartmanni measure usually 6 to 8 µm

Endolimax nana• The trophozoites have one nucleus with a large,

irregularly shaped, blot-like karyosome• Their nucleus has no peripheral chromatin• Their cytoplasm is granular and vacuolated • The trophozoites measure usually 8 to 10

µm (range 6 to 12 µm)• The cysts have 4 nuclei with no chromatoid

bodies• Cysts: 6 to 8 µm (range 5 to 10 µm)

Iodamoeba buetschlii

• The trophozoites have one nucleus with a large, usually central karyosome

• Their cytoplasm is coarsely granular, vacuolated and can contain bacteria, yeasts or other materials

• The trophozoites measure usually 12 to 15 µm (range 8 to 20 µm)

• The cysts have only one nucleus with a large, usually eccentric karyosome

• They do not have chromatoid bodies• Cysts:10 to 12 µm (range 5 to 20 µm)

Entamoeba polecki

• The trophozoites have one nucleus with evenly distributed peripheral chromatin

• Their cytoplasm is coarsely granular, vacuolated and can contain bacteria and yeasts

• The trophozoites measure usually 15 to 20 µm (range 10 to 25 µm)

• The cysts have one nucleus (rarely two) with a small, usually eccentric karyosome

• Cysts: 11 to 15 µm (range 9 to 18 µm) and their shape varies from spherical to oval

Entamoeba histolyticaCharacteristics

• Epidemiology. An infestation source is the human sick of an amoebiasis, or the carrier of dysenteric amoebas

• It is characteristic fecal - an oral path of a transmission of infection (ingestion of cysts with the polluted water, food stuffs)

• Humans of middle age is more often ill

Symptoms

• It begins rather acutely with moderately expressed headache, abdominal pains and body temperature

• One of the symptoms is diarrhoea. • Later 2-5 days from the illness, faecal masses can show

slime and blood• Abdominal pains in the first day are absent or happen very

weak, in some patients they appear only for 5-7th day of illness

• Tenesmuses are observed seldom (at 10 % of patients)

Pathogenesis

• Infestation descends at hit of cysts of a dysenteric amoeba in a digestive tube of the human

• In the initial department of a colon the cyst cover is blasted, and the cyst turns to the luminal form of a dysenteric amoeba

• It is not accompanied by any clinical implications (a healthy carriage)

• In some cases the luminal form takes root into a mucosa, inpours into a submucosa of an intestine and turns to the pathogenic histic form (erythrophage)

Pathogenesis cont…

• Propagating in a tissue of a side of an intestine, the histolytic amoeba causes occurrence of small abscesses in a submucosa which then break in a lumen of an intestine with formation of ulcers of a mucosa

• With disease the number of amoebic ulcers is enlarged• Lesions are seen on all extent of a colon • Hematogenous by the dysenteric amoeba from an

intestine can inpour into a liver and other organs and cause formation there abscesses

• Liver microabscesses are quite often treated as implication of a so-called amoebic hepatitis

The Pathogenesis

• Area most commonly involved = Cecum, then Recto-sigmoid area

• May invade blood vessels causing thrombosis (clotting), infarction and dissemination via portal circulation to liver and extra-intestinal sites e.g. brain, pleura, pericardium and genito-urinary system

• Flask-shaped ulcers

Complications• Intestinal complications of an amoebiasis is owing to

intestine punching, an ameboma, an intestinal bleeding

• The amoeboma represents a tumorous infiltrate in an intestine side, at consecutive infection apposition can abscess.

• The amoebic hepatitis, abscesses of a liver, brain, lungs complications, skin lesions. Liver abscesses and an amoebic hepatitis are more often observed

• The amoebic abscess (abscesses) of a liver can occurboth during the acute season, and after long time (till several years).

Complications• At a blood analysis almost in all cases are defined neutrophilic a

leukocytosis and rising Erythrocyte Sedimentation Rate

• At chronic abscesses intoxication symptoms are expressed weakly, a body temperature subfebrile or normal

• The amoebic abscess can break in surrounding organs and lead to formation of the abscess

• Sometimes the liver abscess breaks through integuments, in these cases in the field of a fistula the amoebic lesion of a skin

• The abscess of lungs arises not only as a result of break of pus from a liver, but also haematogenically

Intestinal amoebiasis, clinical features

We can differentiate 4 different situations inintestinal amoebiasis :

• asymptomatic carriers • amoebic colitis • fulminant colitis • amoeboma

Asymptomatic carriers

• Trophozoites can sometimes remain in the intestinal lumen for years without causing any damage

• The majority (90%) of patients fall into this group.• Asymptomatic carriers have by definition no

symptoms of amoebiasis. • The faeces may show cysts of non-pathogenic E.

dispar or of potentially pathogenic E. histolytica, which for unknown reasons is not invasive.

Amoebic colitis• When Entamoeba histolytica penetrates the intestinal

mucosa it produces ulcerations of the colonic mucosa • The ulcerations are sharply defined and have eroded

undermined edges• This is expressed clinically as abdominal pain, diarrhoea

with blood in the faeces, and only moderate or no fever• When the rectum is affected there is tenesmus (painful

cramps in the anus)• Peri-anal ulcers may occur via direct spread from rectal

amoebiasis

Amoebic colitis cont…

• The ulcers develop rapidly and are painful• After suffering from amoebic colitis there may

be persistent intestinal problems, the aetiology of which is unclear.

Fulminant colitis

• There is sometimes a fulminant course with high fever, a severely ill patient, intestinal bleeding or perforation of the colon

• A slow seepage of intestinal content into the peritoneum is very likely in a severely ill patient

• Condition deteriorates progressively, together with the formation of ileus (intestinal paralysis) and a distended abdomen

• A fulminant course may occur if patients are treated with steroids (e.g. if amoebic colitis is wrongly thought to be haemorrhagic ulcerative colitis)

Amoeboma

• In 1% of patients an inflammatory thickening of the intestinal wall occurs.

• A mass may then be palpated (amoeboma). The diagnosis may be made via biopsy.

• The inflammatory mass may mimick colon carcinoma. • Countless trophozoites are found in the tissues (never

cysts).

Virulence factors of E. histolyticaCysteine proteinase• Degrade host proteins; provide attachment by• degrading mucus and debris and• stimulating host cell proteolytic cascadesAmebapore• Stored in cytoplasmic granules and released

following target cell contact • forms ion channels in the membranes of both

eukaryotic cells and phagocytosed bacteria

Virulence factors of E. Histolytica cont...

• May be directly responsible for the cytolysis of host cells by the parasite

Gal/GalNAc-binding lectin• Target cell adherence; contact-dependent• cytotoxicity; complement resistance• Plays critical and important roles in the

pathogenicity of parasite

DiagnosisMicroscopy• This method cannot differentiate among protozoan with

similar morphological features• Stool specimens can be examined either unstained or

stained with Lugol’s or D’Antoni’s iodine• When amoebic dysentery is suspected, a fresh faecal

sample or a swab from a rectal ulcer should be examined under a microscope

• If examined quickly (a fresh stool, still warm) the colourless motile trophozoites can be seen

• Motility disappears when cooled, and the parasites are then difficult to recognise, only the cyst can then be seen

Diagnosis cont…

Culture and Isoenzymes• Robinson medium and TYSGM-9 of Diamond are

more often used for cultivation of E. histolytica. • Cultivation by Diamond, TYI-S-33 is one of the most

widely used media• Culturing E. histolytica from stool or liver abscess

samples and performing the isoenzyme analyses are mostly unsatisfactory and not useful in routine laboratory practice

Diagnosis cont…

Molecular biology-based diagnosis (PCR)• The PCR method offers sensitivity and specificity for

the diagnosis of intestinal amoebiasisSerological Technique• ELISA, IFA etc• Immunoassay kits are commercially available that

detect E. histolytica. Currently, these tests require the use of fresh or frozen stool specimens and cannot be used with preserved specimens

Diagnosis cont…

Rapid immunochromatographic cartridge assay• This assay is quick and easy to perform and no

special equipment is needed • A rapid cartridge is available that detects

antigens of E. histolytica/E. dispar, however this assay does not distinguish between E. histolytica and E. dispar

• Stool samples must be fresh or frozen and should not be concentrated prior to testing

Bacillary and Amoebic dysentery

• In dysentery it is important to distinguish between bacillary and amoebic dysentery since their treatment is completely different

Bacillary dysentery Amoebic dysentery

Acute onset Gradual onset

Poor general condition General condition normal

High fever Little fever (adult)

Severe tenesmus Moderate tenesmus

Dehydration frequent Little dehydration (adult)

Faeces: no trophozoites Trophozoites present

Treatment

• Metronidazole (Flagyl) or Tinidazole (Fasigyn)• Tetracycline• Diloxanide furoate (Furamide) etc

Prevention• Improved sanitation and clean water supply reduce fecal-oral transmission• Boiling water, Washing vegetables with vinegar• Generally through good personal hygiene

• Factors contributing to faecal-oral spread:– Poor education– Poverty and overcrowding– Unsanitary conditions– HIV infection

Pathogenic and opportunistic free-living amoebae

Naegleria fowleri and Acanthamoeba spp

Introduction

• Acanthamoeba is an opportunistic pathogens causing infections of the central nervous system, lungs, sinuses and skin, mostly in immunocompromised humans

• N. fowleri, causes an acute and fulminating meningoencephalitis in immunocompetent children and young adults

• Naegleria fowleri exists in nature in three forms: a cyst, a trophozoite (ameboid) and a flagellate

Introduction cont…

• Naegleria fowleri and Acanthamoeba spp., commonly found in lakes, swimming pools, tap water, and heating and air conditioning units

• While only one species of Naegleria is known to infect humans

• Several species of Acanthamoeba are implicated, including A. culbertsoni, A. polyphaga, A. castellanii etc

Life Cycle• Naegleria fowleri is found in nature in warm water bodies as

amoeboid and amoeboflagellate trophozoites• Cysts also occur in nature, but not in human infections• Infection occurs during swimming or diving with the parasites gaining

access, through the olfactory neuroepithelium, to the brain• Acanthamoeba spp. occur in the same environments, but are also

found in soil and dust as well as more restricted liquid environments such as humidifiers and dialysis units

• Acanthamoeba spp. do not have an amoeboflagellate form, and cysts can be found in human infections

• Infections due to Acanthamoeba spp. occur more frequently in debilitated or chronically ill individuals, and reach the central nervous system by haematogenous dissemination from foci in the lungs, skin, or sinuses

Clinical features Naegleria fowleri• Acute primary amoebic meningoencephalitis (PAM) is caused by

Naegleria fowleri• It presents with severe headache and other meningeal signs,

fever, vomiting, and focal neurologic deficits, and progresses rapidly (<10 days) and frequently to coma and death

• In humans, N. fowleri can invade the CNS via the nose (specifically through the olfactory mucosa and cribriform plate of the nasal tissues)

• The penetration initially results in significant necrosis of and hemorrhaging in the olfactory bulbs

• From there, the amoebae climbs along nerve fibers through the floor of the cranium via the cribriform plate and into the brain

Clinical features cont…

• The organism begins to consume cells of the brain piecemeal by means of a unique sucking apparatus extended from its cell surface

• It then becomes pathogenic, causing (PAM) • PAM usually occurs in healthy children or

young adults with no prior history of immune compromise who have recently been exposed to bodies of fresh water

Clinical features cont…

Acanthamoeba spp.• Causes mostly subacute or chronic granulomatous

amoebic encephalitis (GAE), with a clinical picture of headaches, altered mental status, and focal neurologic deficit, which progresses over several weeks to death

• In addition, Acanthamoeba spp. can cause granulomatous skin lesions and, more seriously, keratitis and corneal ulcers following corneal trauma or in association with contact lenses

Laboratory Diagnosis• In Naegleria infections, the diagnosis can be made by

microscopic examination of cerebrospinal fluid (CSF)• A wet mount may detect motile trophozoites, and a

Giemsa-stained smear will show trophozoites with typical morphology.

• In Acanthamoeba infections, diagnosis can be made from microscopic examination of stained smears of biopsy specimens (brain tissue, skin, cornea) or of corneal scrapings, which may detect trophozoites and cysts

• Cultivation of the causal organism, and its identification by direct immunofluorescent antibody, may also prove useful

Laboratory Diagnosis cont…

• N. fowleri can be grown in several kinds of liquid axenic media or on non-nutrient agarplates coated with bacteria

• Escherichia coli can be used to overlay the non-nutrient agar plate and a drop of CSF sediment added to it

• Research is focused on development of real time PCR diagnostic methods

Treatment

• Eye and skin infections caused by Acanthamoeba spp. are generally treatable

• Propamidine isethionate (Brolene) plus neomycin-polymyxin B-gramicidin ophthalmic solution has been a successful approach

• Although most cases of brain (CNS) infection with Acanthamoeba have resulted in death, patients have recovered from the infection with proper treatment

Treatment cont…

• Currently, if N. fowleri infection is diagnosed or suspected treatment Amphotericin B is the standard of care

• Amphotericin B is is administered intravaneously and is something of a ‘last resort’ drug as it has high toxicity

• While not particularly effective, every one of the 4 documented survivors of PAM have been treated with Amphotericin B

Ø Pathogenic factor• One potential player that makes it pathogenic is the motility of

the amoeba in the Nfa1 protein

Prevention

• Currently there are no widespread efforts for prevention because of the low prevalence of N. fowleri infections

• However, because of the fatality of the ensuing meningoencephlitis efforts can be made for increased awareness of N. fowleri and its infection for more accurate reporting