Amebiasis

-bhanu chalise

• Harboring(infection) of protozoa Entamoeba histolytica inside the body with or without the disease is called amoebiasis.

• Associated with high mortality and morbidity

• Major public health problem globally• 2nd leading cause of death due to parasitic

disease ( 1st being malaria )

Epidemiology• 10% of population infected globally• About 100,000 deaths occur every year globally• High prevalence in tropics and subtropics• Risk factors: Developing countries Developed countries

travelers immigrants homosexual men HIV positive immunodeficiency states

poverty

Ignorance

overcrowding

Poor sanitation

malnutrition

Causative organism

3 species of entamoeba: E. dispar : E. moshkovskii : E. histolytica

Only E. histolytica is pathogenic. Other two species are apparently non-pathogenic and cause most of the asymptomatic cases.

Morphology• Different form of E. histolytica: 1- trophozoite 2- precyst 3- cyst(1, 2, 4 nuclei)• Quadrinucleated cyst is the infective stage

oval/round resistant to chlorination destroyed above 55 degree celsious and with disinfectants

• Trophozoite stage is feeding vegetative form which is destructive to tissue

Trophozoites of Entamoeba histolytica with ingested erythrocytes (trichrome stain)

The ingested erythrocytes appear as dark inclusions. Erythrophagocytosis is the only morphologic characteristic that can be

used to differentiate E. histolytica from the nonpathogenic E. dispar.

                                          

               

        F E

Virulence factorsTrophozoites of E. histolytica interact with host through a series of steps:

Adhesion of target cell, cytopathic effect E.histolytica induces both Humoral and cell

mediated immune responses Causes disease only when invade the

Intestine Virulence is associated with secretion of

Cysteine proteinase (histolysin) which assists the organism in digesting the extracellular matrix and invading tissues

Cysts of Entamoeba histolytica /E. dispar

• GHI

                                            

                  

                                          

                  

                                          

                  I H GCysts of Entamoeba histolytica/E.

dispar, permanent preparations stained with trichrome.

 

Transmission1) feco-oral(direct hand-to-mouth contact)2) Veneral transmission among homosexual males3) Food or drink contaminated with feces containing the E.

histolytica cyst4) Use of human feces (night soil) for soil fertilizer5) contamination of foodstuffs by flies, and possibly

cockroaches

a single cyst is sufficient to cause the disease Asymptomatic human( the only host) cyst

carriers are the principle reservoir of infection.

Pathogenesis Ingestion of

cysts Excystation in small intestine

Production of 8 trophozoites

Multiplication and Colonization in large intestine

Tissue invasion and destruction

Flask – shaped ulcers(mostly in

caecum, transverse and sigmoid colon

Encystation and exit from

host in the stool

Migrate via Blood

stream( portal circulation) to

the liver Amoebic liver abscess

Clinical featuresIntestinal • Asymptomatic

carriers(90%)• Amoebic colitis• Fulminant colitis• Amoeboma

Extraintestinal• Liver • Lung • brain • skin

Incubation period : varies from weeks to months : average= 3-4 weeks

Asymptomatic carriers -90% without symptoms(non-invasive) - lumen not damaged(cyst passers)Invasive forms: Amoebic colitis/dysentery - flask shaped ulcers superficial or deep - abd.pain, watery/mucoid blood-streaked foul-smelling diarrhoea - fever, tenesmus, peri-anal ulcers - sometimes intermittent diarrhoea alternating constipation Fulminant colitis - <0.5% - severely ill with high fever - profuse bloody diarrhea - perforation(diffuse tenderness) - paralytic ileus -pronounced leukocytosis

• ulcers with raised borders• little inflammation between lesions

Amoeboma- 1% of cases- inflammatory thickening of intestinal wall- palpable mass with trophozoites

Symptoms of amoebic colitisSymptoms Percentage

Diarrhea 100 Dysentery 99 Abdominal pain 85 Fever 68 Dehydration 5

Complications: toxic megacolon, amoeboma, cutaneous amoebiasis, rectovaginal fistula

Amoebic v^s Bacillary Dysentery symptoms Amoebic dysentery Bacillary dysentery Occurrence Usu. In the form of sporadic cases Usu. In the form of outbreaks

Onset gradual Acute

Fever Usu. Low grade (may be high in case of liver abscess)

High grade

Tenesmus/Abd. Cramps Moderate Very severe

Stool Foul- smelling Not foul-smelling

RBCs In clumps Discrete

Pus cells Scanty Numerous

Eosinophils Present Absent or rare

Bacteria Numerous, motile Scanty, non-motile

E. histolytica Trophozoites + Absent

Growth on culture Negative Positive

Extra-intestinal

Amoebic liver abcess(most common) - 5% of invasive disease - 10 times more common in men -Usually no bowel symptoms except sometimes -right upper quadrant tenderness - hepatomegaly - jaundice(10- 15%)Pleuropulmonary/pericardial

- direct spread(transdiaphragmatic rupture) from liver abscess (10%) - hematogenous spread -cough with crepitation

Similarly infection can spread to brain, skin and genitourinary system

Investigation

Parasite detection Antibody detection

Antigen detection PCR and other tests

Investigation

Parasite detection1. Direct saline(wet) mount of feces:

- most common microscopic technique-sample examined within 1 hour of collection-3 stool samples taken on consecutive day ( since

sensitivity increased from 60% to 90%)-presence of ingested erythrocytes within trophozoites is

pathognomic for E. histolytica-carriers have only cysts in their stool Misidentification: macrophages v^s trophozoites : PMN v^s cysts : other entamoeba

2. Various culture techniques are available but not done routinely

Antibody detection tests

• Routinely employed for extra-intestinal dz– Positive(75%)- at presentation and 90%- beyond

1st week of symptoms– ELISA is most sensitive – IHA– Latex agglutination– Immunoelectrophoresis and immunodiffusion

Antigen detection• ELISA kits( sensitivity>90%): used in

epidemiological studies ; useful in endemic areas

• Antigen detection by ELISA: is the ideal test – distinguishes current from past infection.

PCR OTHER TESTS: chest radiograph

: CT , MRI : sigmoidoscopy : peripheral blood- leukocytosis without eosinophillia, mild anemia : Alp, ESR are common lab findings.

• raised immobile right diaphragm• Other imaging modalities show

– A single abscess in the right or left lobe

– Multiple lesions can be present

Imaging

None of these modalities can

differentiate amebic abscess from pyogenic

or malignant one

Treatment of amebiasis -combination of a luminal and a tissue amoebicide is advocated for complete parasite clearance in Invasive disease

Luminal amoebicides• Diloxanide furoate• diiodoquinol• paromomycin

Tissue amoebicides• 5-nitroimidazoles(DOC) -metronidazole -tinidazole -secnidazole• Chloroquin• Dehydroemetine

Amoebic colitis: metronidazole followed by a luminal agentFulminant amoebic colitis: add an antibiotic to deal with bowel floraAmoebic liver abscess: tissue amoebicide followed by luminal agent

treatment continued…………………

Asymptomatic intestinal carriers : a luminal agentTreatment for only E. dispar is not nessary Most patients show a response to a treatment( reduced

fever and abdominal pain) within 72-96 hrs.Percutaneous therapeutic aspiration guided by ultrasound

or CT is reserved for: -when lesion in the left lobe of liver -when diagnosis is uncertain - no response to metronidazole( persistent fever and abd. pain) after 4 days of treatment -large(>8-10 cm) ie. >300 ml of fluid -severly ill patients

Amoebicide Pediatric dose Adult dose

Metronidazole 35-50 mg/kg/day for 7-10 days( in 3 divided doses)

750 mg 8 hourly

Tinidazole 50 mg/kg/day for 3 days(once daily)

2 g once a day

Paromomycin 25-35mg/kg/day for 7 days(in 3 divided doses)

25-35mg/kg/day (in 3 divided doses)

Diloxanide furoate 20mg/kg/day for 7 days(in 3 divided doses)

500mg 8 hourly

Iodoquinone 30-40mg/kg/day for 20 days(in 3 divided doses)

650mg 8 hourly

DRUGS AND DOSES

PREVENTION & CONTROL Primary prevention

Safe excreta disposal Safe water supply Hygiene Health education Treat symptomatic carriers Treat water(iodine, boiling): NOT

chlorine Secondary

Early diagnosis Treatment

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