Shabnam tehrani , MD Assistant Professor of - PowerPoint Presentation

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Shabnam tehrani , MDAssistant Professor of Shahid Beheshti University of Medical science

Amebiasis

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DefinitionAmebiasis is infection with the parasitic intestinal protozoan Entamoeba

histolytica

(the "tissue-

lysing

ameba

").

Most infections are probably

asymptomatic

, but

E.

histolytica

can cause disease

ranging from dysentery to

extraintestinal

infections, including liver abscesses.

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Life Cycle and TransmissionE. histolytica exists in two stages

:

-

a hardy multinucleate

cyst form

-the

motile

trophozoite

stage

.

Infection is

acquired by

ingestion

of cysts contained in

fecally

contaminated food or

water.

Trophozoites

can live within the large-bowel lumen without causing disease or can invade the intestinal mucosa, causing amebic colitis

.

In some cases,

E.

histolytica

trophozoites

invade through the mucosa and into the bloodstream, traveling through the portal circulation to reach the

liver and causing amebic liver abscesses.

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EpidemiologyIt was a staple of most textbooks that 10% of the world's population was infected with E.

histolytica

.

We now know that most asymptomatic individuals harboring amebic

trophozoites

or cysts in their stools are infected with a

noninvasive species

:

Entamoeba

dispar

E

.

histolytica

infections are most common in areas of the world where

poor sanitation and crowding

compromise the barriers to contamination of

food and drinking water

with human feces.

Endemic

areas include parts of Mexico, India, and nations in the tropical regions of Africa, South and Central America, and Asia.

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Pathogenesis and PathologyE. histolytica trophozoites

possess a potent repertoire of

adhesins

,

proteinases

, pore-forming

proteins

Disease begins when

trophozoites

adhere to colonic mucosal epithelial

cells,then

disruption

of the colonic

mucin

barrier

secreting

proteolytic

enzymes(

histolysine

) and

cytotoxic

substances.

contact-dependent cell killing

cytophagocytosis

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Clinical SyndromesIntestinal Amebiasis

:

Most patients

are

asymptomatic

, but individuals with

E.

histolytica

infection can develop disease

.

Symptoms of amebic colitis generally appear

2–6 weeks

after ingestion of the cyst form of the parasite

.

Diarrhea

(classically

heme

-positive) and

lower abdominal pain

are the most common symptoms.

Malaise

and weight loss may be noted as disease progresses.

Severe

dysentery

, with

10–12

small-volume,

blood

- and mucus-containing stools daily, may develop, but only 40% of patients are febrile

.

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…Fulminant amebic colitis

, with even more profuse diarrhea, severe abdominal pain (including peritoneal signs), fever, and pronounced

leukocytosis

are rare, disproportionately affecting

young children, pregnant women, individuals being treated with

glucocorticoids

, and possibly individuals with diabetes or alcoholism.

Mortality rates from

fulminant

amebic colitis: 40%

Recognized complications of amebic colitis also

include

-

toxic

megacolon

(documented in 0.5% of patients with colitis), with severe bowel dilation and intramural air,

-

ameboma

, which presents as an abdominal mass that may be confused with colon cancer.

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…B.Amebic

Liver

Abscess:

Most

individuals with amebic liver abscess do not have concurrent signs or symptoms of colitis, and most do not have

E.

histolytica

trophozoites

in their stools

.

The exceptions are individuals with

fulminant

amebic colitis, in which concurrent amebic liver abscess is not uncommon

.

Disease can arise from months to years after travel to or residence in an endemic area; therefore, a careful travel history is key in making the diagnosis.

The

classic presentations of amebic liver abscess are

RUQ pain

, fever, and hepatic tenderness. The pace of disease is usually acute, with symptoms lasting <10 days.

Jaundice

is unusual, but dullness and

rales

at the right lung base (secondary to pleural effusion) are common.

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This is an amebic abscess of liver. Abscesses may arise in liver when there is seeding of infection from the bowel, because the infectious agents are carried to the liver from the portal venous circulation.

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Diagnostic TestsThe diagnosis of amebic colitis has traditionally been based on the demonstration of E. histolytica trophozoites

or cysts in the stool or colonic mucosa of patients with diarrhea

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…However, the inability of microscopy to differentiate between E. histolytica

and other

Entamoeba

species, such as

E.

dispar

limits its effectiveness as a sole diagnostic method.

Examination

of

3 stool

samples improves sensitivity for the detection of

Entamoeba

species, and it has been argued that the

presence of amebic

trophozoites

containing red blood cells in a

diarrheal

stool is highly suggestive of

E.

histolytica

infection

.

Despite these inherent limitations, microscopy, often

combined

with serologic testing, remains the

standard diagnostic

approach.

Culture of stools for

E.

histolytica

trophozoites

serves as a research tool but is generally not available for clinical use.

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…PCR assay for DNA in stool

samples is currently the most sensitive and specific method for identifying

E.

histolytica

infection and has become a valuable epidemiologic and research

tool

Commercially available tests that use enzyme-linked

immunosorbent

assays (

ELISAs)

or

immunochromatographic

techniques to detect

Entamoeba

antigens are less expensive and more easily performed and are being used with increasing frequency.

At this point, antigen detection–based

ELISAs

that can

specifically

identify

E.

histolytica

in stool probably represent the

best choice in endemic

areas

In

instances in which

amebiasis

is suspected on clinical grounds in a patient with acute colitis but initial stool samples are negative,

colonoscopy

with examination of brushings or mucosal biopsies for

E.

histolytica

trophozoites

may be helpful in making the diagnosis or in identifying other diseases, such as inflammatory bowel disease or

pseudomembranous

colitis.

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…The diagnosis of amebic liver abscess is based on the detection (generally by ultrasound or CT)

of

one or more space-occupying lesions in the liver and a positive serologic test for antibodies to

E.

histolytica

antigens.

Amebic

liver abscesses

are classically described as single,

large, and located in the right lobe of the liver

, but sensitive imaging techniques have shown that multiple abscesses are more common than previously suspected.

When

a patient has a space-occupying lesion of the liver, a positive amebic serology is highly sensitive (>94%) and highly specific (>95%) for the diagnosis of amebic liver abscess.

False-negative

serologic

tests have been reported when serum samples were obtained

very early

in the course of abscess (within 7–10 days of onset), but repeat tests are almost always positive

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TreatmentAmebic Colitis or Liver Abscess:Tinidazole

: Better tolerate & more effective for: colitis and liver abscess(2

gr

/d. 3 d

)

Metronidazol

:

(750 mg

tid

po

or IV

5-10 d

)

Entamoeba

histolytica

Luminal Infection

:

Paromomycin

: 30mg/kg

tid

po

5-10

d

Idoquinol

: 650 mg

tid

po

20d

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Giardia

lamblia

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…Giardiasis is one of the most common parasitic diseases in both developed and developing countries worldwide, causing both endemic and epidemic intestinal disease and diarrheaInfection follows the ingestion of environmentally hardy cysts, which

excyst

in the small intestine, releasing flagellated

trophozoites

Giardia

remains a pathogen of the proximal small bowel and does not disseminate

hematogenously

World

wide distribution

Highest

incidence in children, young adults in late summer.

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Transmission1-Person to person transmission

2-

Water sports, surface contamination. Watershed contamination

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Clinical Manifestationsrange from asymptomatic carriage to fulminant diarrhea and

malabsorption

.

Most infected persons are asymptomatic, but in epidemics the proportion of symptomatic cases may be higher.

Symptoms

may develop suddenly or

gradually

In

persons with acute

giardiasis

, symptoms develop after an

IP

that lasts at least 5–6 days and usually 1–3 weeks

.

Prominent early symptoms include diarrhea, abdominal pain, bloating,

flatus, nausea, and vomiting.

Although

diarrhea is common, upper intestinal manifestations such as nausea, vomiting, bloating, and abdominal pain may predominate.

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…The duration of acute giardiasis is usually >1 week, although diarrhea often subsides.Some

persons who have relatively mild symptoms for long periods recognize the extent of their discomfort only in retrospect.

Fever

, the presence of blood and/or mucus in the stools, and other signs and symptoms of colitis are uncommon and suggest a different diagnosis or a concomitant illness.

Because

of the less severe illness and the propensity for chronic infections, patients may seek medical advice late in the course of the illness; however, disease can be severe, resulting in

malabsorption

, weight loss, growth retardation, and

dehydration.

Giardiasis

can be severe in patients with

hypogammaglobulinemia

and can complicate other preexisting intestinal diseases, such as that occurring in cystic fibrosis. In patients with AIDS,

Giardia

can cause enteric illness that is refractory to treatment.

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DiagnosisGiardia

should be identified 50 to 70% of the time after one stool, and 90% identification after 3

stools

Biopsy tissue/duodenal aspirate stained by

trichrome

or

Giemsa

stain. 

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Drugs Dose

Metronidazole

250mgtidX 5-7 d

Nitazoxanide

500mg bdX3d

Paromomycin

25–30 mg/kg/d in 3 doses × 5–10 d

Tinidazole

2 g × 1 dose

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TreatmentDrugs Dose

Metronidazole

250mg

tidX

5-7 d

Nitazoxanide

500mg bdX3d

Paromomycin

25–30 mg/kg/d in 3 doses × 5–10 d

Tinidazole

2 g × 1 dose

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PreventionThe prevention of giardiasis

requires proper handling and

treatment of water

Good

personal hygiene

on an individual basis

Chlorination alone

is sufficient to kill

G.

lamblia

cysts, important variables, such as water temperature, clarity, pH, and contact time, alter the efficacy of chlorine, and higher chlorine levels (4 to 6 mg/liter) may be required.

Bringing

water to a boil

is sufficient to kill all

protozoal

cysts; at high altitudes, boiling for longer periods may be necessary