AMEBIASIS & GIARDIOSIS

AMEBIASIS

AMEBIAS PATHOGENS

Intestinals Entamoeba histolytica

Tisulares (Amebas of Libra) AcanthamoebaNaegleria

AMEBIAS INTESTINALS

EntamoebaE.histolytica (pathogen)E. coliE. hartmaniE. gingivalis (oral)

Endolimax nanaIodamoeba butschlii

AMEBIC DYSENTERYCausal agent: Entamobea histolytica is well recognized as a pathogenic amoeba.

Geographic Distribution: Worldwide, with higher incidence of amebiasis in developing countries .

In industrialized countries, risk groups include male homosexuals, travelers and recent immigrants, and institutionalized populations.

History: Loosh was first described in 1875

MORPHOLOGYDifferent form of E. histolytica ;

1 -Trophozoite

2 -Precyst

3 -Cyst(1, 2, 4 nuclei)

TROPHOZOITE CHARACTERSize: 12-60μm in diameter ;

Non-invasive form ( minuta) / E. dispare

Invasive form (magna) contain RBC, E. histolyticaPseudopodiaMotility

EctoplasmEndoplasm: may be contain ingested RBC

Nucleoplasm

Non-invasive forminvasive form

DIFFERENT FORM OF E.HISTOLYTICA CYST

LIFE CYCLE

Life cycle

EPIDEMIOLOGY

Prevalence of amebic infection varies with level of sanitation and generally higher in tropics and

subtropics than in tempearate climates .

*Worldwide prevalence is about 10% to 50%*Cyst passers are important source of infection

The true estimated prevalence of E. histolytica is close to 1% worldwide.

Entamoeba histolytica is the second leading cause of mortality due to parasitic disease in

humans. (The first being malaria). Amebiasis is the cause of an estimated 50,000-100,000 deaths

each year.

TRANSMISSION

1-Direct contact of person to person( fecal-oral).

2 -Veneral transmission among homosexual males( oral-anal) . 3- Food or drink

contaminated with feces containing the E.his. Cyst.

4 -Use of human feces (night soil) for soil fertilizer.

5 -Contamination of foodstuffs by flies, and possibly cockroaches.

PATHOGENESIS

Effective factores:

1 -strain virulence

2 -susceptibility of the host; nutrition status, immune-sys.

3 -breakdown of immunologic barrier (tissue invasion)

PATHOGENICITY MECHANISMS

1 -secreting proteolytic enzymes( histolysine ) and cytotoxic substances.

2 - contact-dependent cell killing

3 – cytophagocytosis

Amebic killing target cell :

1 -receptore-mediated adherence of amebae to target cell ( adherence lectin)

2 -amebic cytolysis of target cell 3 -amebic phagocytosis of killed target cell

CLINICAL SYMPTOMS(2-6W AFTER INGESTION)

Asymptomatic infection Symptomatic infection

Intestinal Amebiasis Extraintestinal Amebiasis

Dysenteric(40% Fever) Non-Dysenteric colitis Hepatic Pulmonary(R) The extra foci(p,p,b)

( Fulminant,perfuration

Toxic megacolon) Liver abscces Acute nonsupprative

Intestinal Amebiasis symptoms: Diarrhea or dysentery,Lower abdominal pain, cramping , anorexia, weight loss, chronic fatigue

PATHOLOGY OF AMEBIASIS

FLASK-LIKE ULCER

EXTRA-INTESTINALAMEBIASIS

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.

DIAGNOSIS

Paraclinical Diagnosis:Sigmoidoscopic examination:

precence of a grossly normal mucosa between the ulcers serves to differentiate amebic from bacillary

dysentery,( the entire mucosa being involvoed in bacillary dysentery).

HepatomegallyC.B.C. : leukocytosis in Amebic dys. rises above

12000 per microliter, but counts may reach 16000 to 20000 per microliter.

LABORATORY DIAGNOSIS

Entamoeba histolytica must be differentiated from other intestinal protozoa including: E. coli, E. hartmanni, E.

dispare……,

Differentiation is possible, but not always easy, based on morphologic characteristics of the cysts and trophozoites.

  The nonpathogenic Entamoeba dispar, however, is

morphologically identical to E. histolytica, and differentiation must be based on isoenzymatic or

immunologic analysis .

Molecular methods are also useful in distinguishing between E. histolytica and E. dispar and can also be

used to identify E. polecki .

MICROSCOPY

Microscopic identification

This can be accomplished using:

Fresh stool: wet mounts and permanently stained preparations (e.g., trichrome) .

Concentrates from fresh stool: wet mounts, with or without iodine stain, and permanently

stained preparations (e.g., trichrome) .

TROPHOZOITES OF ENTAMOEBA HISTOLYTICA /E. DISPAR ( TRICHROME STAIN )

 

Microscopy

 AB

 

In the absence of erythrophagocytosis, the pathogenic E. histolytica is morphologically indistinguishable from the nonpathogenic E. dispar!

  Each trophozoite has a single nucleus, which has a centrally placed karyosome and uniformly distributed peripheral chromatin.

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 .

               

        

                                          

EF

CYSTS OF ENTAMOEBA HISTOLYTICA /E. DISPAR

GHI

                                                                                                                                                                                        

GHICysts of Entamoeba histolytica/E. dispar, permanent preparations stained with trichrome.

 

IMMUNODIAGNOSIS1 -Antibody detection :

The indirect hemagglutination (IHA)

The EIZA test detects antibody specific for E. histolytica in approximately 95% of patients with

extraintestinal amebiasis, 70% of patients with active intestinal infection, and 10% of asymptomatic persons

who are passing cysts of E. histolytica  .

2 -Antigen detection may be useful as an adjunct to microscopic diagnosis in detecting

parasites and to distinguish between pathogenic and nonpathogenic infections .

Recent studies indicate improved sensitivity and specificity of fecal antigen assays with

the use of monoclonal antibodies which can distinguish between E. histolytica and E.

dispar infections .

MOLECULAR DIAGNOSIS

In reference diagnosis laboratories, stool PCR is the method of choice for discriminating

between the pathogenic species (E. histolytica) from the (nonpathogenic species

(E. dispar.

TREATMENT

Amebic Colitis or Liver Abscess:Tinidazole: Better tolerate & more effective for: colitis

and liver abscess(2 gr.3d)Metronidazol: Parenteral available (750 mg tid po or

IV 5-10d)

Entamoeba histolytica Luminal Infection:

Paromomycin: 30mg/kg tid po 5-7 dIdoquinol: 650 mg tid po 20d

Giardia lamblia

Source: http://soils.cses.vt.edu

The genus Giardia belongs to the class Zoomastigophorea, the order Diplomonadida, and the family Hexamitidae .

It is one of the most primitive eukaryotes: it has a small subunit ribosomal RNA sequence and no mitochondria and Golgi apparatus

Now Giardia can be classified according to antigen, isoenzyme, and genetic analysis in addition to their morphology and host range.

Species identified

Giardia lamblia (intestinalis, duodenalis) - humans, mammals

Giardia muris - mammals

Giardia ardeae - birds

Giardia psittaci - birds

Giardia agilis - amphibians

Of the Giardia species, only G. lamblia has been successfully cultured in vitro.

The trophozoite divides by longitudinal binary fission

Two morphological forms: Trophozoite and cyst ( infective form)

Tear drop shaped2 adhesive discs ,

2 median bodies,2 nuclei

4 pairs of flagella

Source: www.sd01.k12.id.us

Tear drop shaped2 adhesive discs ,

2 median bodies,2 nuclei

4 pairs of flagella

Source: www.sd01.k12.id.us

intracytoplasmic projections axonemes

Source: http://medlib.med.utah.edu

Haematoxilyn staining

two nuclei, each with a prominent central karyosome (characteristic

facelike image(

Source: Gallery of histology Woods and Ellis2000

8 to 12 mm long and 7 to 10 mm wide

convex dorsal surface

a flat ventral surface sucking or adhesive disk

four pairs flagellae

Source: http://soils.cses.vt.edu

Epidemiology

Host can be humans, primates, cats, dogs, calves ,beavers, rabbits, etc .

World wide distribution

Highest incidence in children, young adults in late summer .

Transmission

1 -Person to person transmission

2 -Water sports, surface contamination. Watershed contamination

3 -sexually active male homosexuals and persons in custodial institutions.

Pathogenesis and Immune response (1)

•The production of diarrhea, and occasionally malabsorption, is the result of a complex interaction of Giardia with the host ,

•Infection occurs after oral ingestion of as few as 10 to 25 cysts.

•After excystation, trophozoites colonize and multiply in the upper small bowel

•Adherence of G. lamblia in the human gut may be via the disk,

but may also involve specific receptor-ligand interactions

Pathogenesis and Immune response (2)

Several pathogenic mechanisms have been postulated

Disruption of the brush border

Mucosal invasion

Elaboration of an enterotoxin

Stimulation of an inflammatory infiltration leading to fluid and electrolyte secretion and occasionally to villous changes

TEM micrograph showing the method of attachment to the duodenal wall.

Ventral sucking discSource: Gallery of histology Woods and Ellis2000

Immune Response

Partially protective immunity may develop to Giardia

Immune response involves both cellular and humoral immunity

-Ig A, serum Ig G and Ig M are detected in patients: role of Ig A is not completely understood, probably inhibits trophozoite attachment

-IgA deficiency lead to chronic giardiasis

-Cell mediated immune response may also play a role

Human milk may also play a role in protection of the host against Giardia : Free fatty acids and IgA antibodies

Infection with G. lamblia includes1 -Asymptomatic cyst passage (5 to 15% ) •acute self-limited diarrhea (25 to 50% )

•and a chronic syndrome of diarrhea •malabsorption, and weight loss

2 -Symptomatic giardiasis is characterized by •acute onset of diarrhea ,

•abdominal cramps, bloating, and flatulence •feelings of malaise, nausea, and anorexia

•may complain of sulfuric belching •Vomiting, fever, and tenesmus occur less commonly .

•stools may be profuse and watery, but later they are commonly greasy, and foul-smelling and may float

The role that chronic infection with Giardia plays in the growth and development of children in the developing world has been controversial

Life Cycle

Trophozoites : Lives in duodenum, jejenum and upper ileum

They come in close contact to the mucosal, but do not invade the host. Adhesive disc fits over surface of epithelial cell

The flagella act as a pump to move nutrients away from the microvilla and hold the adhesive disc near the mucosa.

Rapid division to produce large numbers quickly

Source: Doug Allington

14 billion parasites in diarrheic stool (trophozoites only) Moderate infection: 300 million cysts.

As the organism traverses the colon it is stimulated to encyst .

Produce an oval cyst with thick walls, with 2-4 nuclei .

Dividing within cyst (4 nuclei is older cyst)

Complete division in duodenum of host after ingestion

Cyst is approximately 8-10m and ellipsoid in shape .

The cyst is the infective state and is transferred by the fecal-oral route.

Diagnosis

• Giardia should be identified 50 to 70% of the time after one stool, and 90% identification after three stools

• Wet, saline mounts: falling leaf motion, fibrils present, and nucleic characteristics.

• Biopsy tissue/duodenal aspirate stained by trichrome or Giemsa stain .

• Enzyme immunoassay and fluorescent-anitbody monoclonal antigen detection systems

• Sensitivity & specificity: 90-100% (ProSpec T, GiardEIA, MeriFluor, Color Vue, and DD

System (

Source: http://soils.cses.vt.edu

Source: Doug Allington

Source: Doug Allington

Source: http://www. cbc.ca

DrugsDose

Metronidazole250mgtidX 5-7 d

Nitazoxanide500mg bdX3d

Paromomycin 25–30 mg/kg/d in 3 doses × 5–10 d

Tinidazole 2 g × 1 dose

PREVENTION

The 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

Artistic impression by Russel KightleySource: http://soils.cses.vt.edu