amoebiasis - bowenstaff.bowen.edu.ng
TRANSCRIPT
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
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.
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
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