Parasitology-Lec 10 Entamoeba

PARASITOLOGY LECTURE 10 – Intestinal Amebae, Commensal Amebae and Free-Lining Pathogenic Amebae Notes from Rivera,PT, Rivera,WL and Solon,JAA USTMED ’07 Sec C – AsM

• • •

INTESTINAL AMEBAE ENTAMOEBA HISTOLYTICA

•

Classification o subphylum Sarcodina o superclass Rhizopoda o class Lobosea o order Amoebida o family Entamoebidae o genus Entamoeba

DISEASE

•

cause invasive intestinal and extraintestinal disease

life cycle is simple and no intermediate hosts involved extracellularly located and do not undergo antigenic variation Cyst o Quadrinucleate o Resistant to gastic acidity and dessication o Can survive in a moist environment for several weeks o Infection occurs when cysts are ingested from fecally-contaminated material o Modes of transmission  Fecal-oral route  Direct colonic inoculation through contaminated enema equipment o Excystation occurs in the small or large bowel a. nuclear fission b. cytoplasmic division (forms 8 trophozoites)

immature cysts

MORPHOLOGY

•

• • • •

•

a pseudopod-forming nonflagellated protozoan parasite the most invasive in the Entamoeba family (which includes E. dispar, E. hartmanni, E.polecki, E. coli and E. gingivalis) only member of the family to cause colitis and liver abscess a eukaryotic organism cellular features o lack organelles that resemble mitochondria o no ER o no Golgi apparatus o cell surface and secreted proteins contain signal sequences o Ribosomes form aggregated crystalline arrays in the cytoplasm in trophozoite biochemical characteristics o lack glutathione metabolism o uses pyrophosphate instead of ATP at several steps in glycolysis o inability to synthesize purine nucleotides de novo o glucose is actively transported into cytoplasm o end products of metab are EtOH and CO2 (acetate in aerobic conditions)

mature cysts

•

LIFE CYCLE

Trophozoites o Highly motile o Possess pseudopodia o Have the ability to colonize and/or invade the large bowel (cysts are never found w/in invaded tissues) o Multiply by binary fission o Encyst a. produces uninucleate cysts b. undergo 2 successive nuclear divisions (forms quadrinucleate cysts)

PATHOGENESIS AND CLINICAL MANIESTATION

•

• • •

2 stages 1. Infective cyst 2. invasive trophozoite form

•

humans are the only known hosts

•

most cases present as asymptomatic infections with cysts being passed out in the stools (cyst carrier state) the non-pathogenic E. dispar has a higher prevalence than E. histolytica most E. histolytica infections are asymptomatic in endemic communities Amebic colitis o Gradual onset of abdominal pain and diarrhea w/ or w/o blood and mucus in stools o Fever occurs only in 1/3 of patients o Intermittent diarrhea alternating with

o

constipation Children may develop fulminant colitis  Severe bloody diarrhea  Fever



o o

Abdominal pain

o o

colitis

•

Ameboma o Occurs in less than 1% of intestinal infections o Mass-like lesion with abdominal pain and history of dysentery o Can be mistaken for carcinoma

•

Amebic liver abscess (ALA) o Most common extra-intestinal form of amebiasis o Cardinal manifestations (most frequent complaints in acute cases {2 weeks duration)  found in older patients  Wasting disease  Weight loss rather than fever o 72% of daily stool cultures harbored trophozoites even in asymptomatic infections o mortality uncomplicated