Amoebiasis (Entamoeba histolytica)

 

Amoebiasis (Entamoeba histolytica) 




  • It is a parasitic infection Caused by Entamoeba histolyticathis
  • This parasite causing diarrhea, dysentery and abscess in man
  • Lambl (1859) first discovered the parasite, Loach (1875) proved its pathogenic nature, while Schaudinn (1903) differentiated pathogenic and non-pathogenic types of amoebae.
  • First identified by doctor (F.Aleksandrovich- 1875) from st.petersburg.
  • Affect the intestinal parts of host.
  • Cased increased diarrohea, abdominal pain, flatulents, gas and increased body temperature.
  • Enter through blood stream from intestine to other organs (liver, lungs, brain).
  • It cause amoebic dysentry
  • Non-pathogenic -  E. Coli, E. Hartmanni, E. Polecki, E. Nana,E. Lodamoeba.
  • These amoebia were colonize as commensals in colon, helps to settle intestine mucosa.
  •  It cause infection in immunocompromised persons - E. Polecki, E. Nana.

Entamoeba histolytica





Morphology

  • Unicellular microorganisms.
  • Their life divided into two stages:
  • The actively motile feeding stage (trophozoite).
  • The quiescent, resistant, infective stage (cyst).
  • Reproduction by binary fission
  • (Splitting the trophozoite)
  • Development of numerous trophozoites within the mature multinucleated cyst.
  • Motility is accomplished by extension of a pseudopod (“false foot”).
  • The amebic trophozoites remain actively motile as long as the environment is favorable.
  • The cyst form develops when the environmental temperature or moisture level drops.
  • Trophozoites- 12-60 micro meter in diameter
  • Covered by three lipid cell membrane,
  • Absorption of food by phagocytosis
  • Trophozoites contain –nucleus, karyosome.
  • Cyst – covered by multilayer membrane (chitin and inter alia)
  • It helps to prevent exchange of substances from internal cyst to environment.


Epidemiology

  • Human pathogen.
  • Present in soil, warm fresh water ponds or swimming pools.
  • E. histolytica has a worldwide distribution.
  • Found in cold areas such as Alaska, Canada, and Eastern Europe,
  • Tropical and subtropical regions
  • Poor sanitation and contaminated water.
  • Asymptomatic carriers carry Trophozoites and cyst and sheading.
  • Flies and cockroaches act as mechanical vectors and carry the cyst from environment.
  • Sewage containing cysts can contaminate water systems, wells, springs, and agricultural (human waste is used as fertilizer).

Physiology and Structure

  • Cyst and trophozoite forms of E. histolytica are detected in fecal specimens from infected patients Trophozoites can also be found in the large intestine.
  • In freshly passed stools, actively motile trophozoites can be seen, whereas in formed stools.

Pathogenesis

  • After ingestion, the cysts pass through the stomach,
  • Gastric acid stimulates release of the pathogenic trophozoite in the duodenum.
  • The trophozoites divide and produce extensive local necrosis in the large intestine.
  • Tissue destruction - Cytotoxin.
  • Attachment of E. histolytica trophozoites – cause tissue necrosis
  • The lysis of colonic epithelial cells, human neutrophils, lymphocytes, and monocytes by trophozoites is associated with a lethal alteration of host cell membrane permeability.
  • Lysis of neutrophils may contribute to tissue destruction.
  • Flask-shaped ulcerations of the intestinal mucosa are present with inflammation, hemorrhage and secondary bacterial infection.
  •  Invasion into the deeper mucosa with extension into the peritoneal cavity may occur.
  • This can lead to secondary involvement of other organs, primarily the liver but also the lungs, brain, and heart.
  • Extra intestinal amebiasis is associated with trophozoites.
  • Amebae are found only in environments that have a low oxygen pressure, because the protozoa are killed by ambient oxygen concentrations.

Life cycle




Symptoms

  • Abdominal cramps
  • Diarrhoea
  • Passing 3-8 semi-formed stool everyday
  • Passing of stool with mucus / blood
  • Gastric – in intestine
  • Fatigue
  • Rectal pain with bowel movement
  • Fever
  • Vomiting
  • Weight loss

Colitis




Lab diagnosis

  • Microscopic
  • Serologic tests,
  • Several immunologic tests for the detection of fecal antigen,
  • Polymerase chain reaction (PCR)
  • DNA-probe assays

Treatment, Prevention, and Control

  • Metronidazole, followed by iodoquinol, diloxanide furoate, or paromomycin.
  • Asymptomatic carriage can be eradicated with iodoquinol, diloxanide furoate, or paromomycin.
  • Adequate sanitation.
  • Education about the routes of transmission.
  • Chlorination and filtration of water supplies.
  • Physicians should alert travelers to developing countries of the risks associated with consumption of water (including ice cubes), unpeeled fruits, and raw vegetables.
  • Water should be boiled and fruits and vegetables thoroughly cleaned before consumption.
  • Avoid uncooked/ uncleaned foods.
  • Drink purified water.


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