PROTOZOA Unicellular, eukaryotic organisms of kingdom Protista (3-2000

m).

Protozoan means “first animal”.

20,000 species, only a few are pathogens.

Most are free-living organisms that inhabit water and soil. Some live in association with other organisms as parasites or symbionts.

Reproduce asexually by fission, budding, or schizogony.

Some exhibit sexual reproduction (e.g.: Paramecium).

Trophozoite: Vegetative stage which feeds upon bacteria and particulate nutrients.

Cyst: Some protozoa produce a protective capsule under adverse conditions (toxins, scarce water, food, or oxygen).

PROTOZOA (Continued) Nutrition Some ingest whole algae, yeast, bacteria, or smaller

protozoans. Others live on dead and decaying matter. Parasitic protozoa break down and absorb nutrients from their hosts.

Some transport food across the membrane. Others have a protective covering (pellicle) and

required specialized structures to take in food.– Ciliates take in food through a cytostome.

Digestion takes place in vacuoles. Waste may be eliminated through plasma membrane

or an anal pore.

Protozoan classification• The groups are:

• flagellates (or Mastigophora)

• amoebae (or Sarcodina)

• sporozoans (or Sporozoa, Apicomplexa) and

• ciliates (or Ciliophora).

Ecological Niches in the Ecological Niches in the Human Body:Human Body:

• 1. Skin: 1. Skin: LeishmaniaLeishmania • 2. Eye: 2. Eye: AcanthamoebaAcanthamoeba • 3. Mouth: 3. Mouth: Amoebae and flagellates Amoebae and flagellates

(usually non-pathogenic) (usually non-pathogenic) • 4.Gut: 4.Gut: Giardia, Entamoeba (and invasion to Giardia, Entamoeba (and invasion to

liver), Cryptosporidium, liver), Cryptosporidium,

Isospora, Balantidium Isospora, Balantidium • 5. G.U. tract: 5. G.U. tract: TrichomonasTrichomonas

Ecological Niches in the Ecological Niches in the Human Body:Human Body:

• 6.6. Bloodstream: Bloodstream: Plasmodium, Plasmodium,

Trypanosoma Trypanosoma

• 7. Spleen: 7. Spleen: LeishmaniaLeishmania

• 8. Liver: 8. Liver: Leishmania, Entamoeba Leishmania, Entamoeba

• 9. Muscle: 9. Muscle: Trypanosoma cruzi Trypanosoma cruzi

• 10. CNS: 10. CNS: Trypanosoma, Naegleria, Trypanosoma, Naegleria,

Toxoplasma, PlasmodiumToxoplasma, Plasmodium

INTESTINAL PROTOZOA

• Pathogenic• Entamoeba histolytica• Balantidium coli• Giardia lamblia• Dientamoeba fragilis• Cryptosporidium parvum• Enterocytozoon bieneusi• Septata intestinalis• Cyclospora cayetanensis• Isospora belli

• Commensal• Entamoeba hartmani• Entamoeba dispar• Entamoeba coli• Endolimax nana• Iodamoeba bütschlii• Chilomastix mesnili• Trichomonas hominis• Blastocystis hominis

Entamoeba histolytica Trophozoites and Cysts

• multiple well defined pseudopodia often extended eruptively

• Differentiation into endo- and ectoplasm

• Spherical nucleus (4-7 m) with small central nucleolus and characteristic radial spokes

Phagocytosis

Trophozoites and Cysts

• Tissue forms often contain phagocytosed RBCs

• Trophozoites encyst and cysts mature as they travel through the colon

• Only mature cysts are infective

Trophozoites and Cysts

Trophozoites and Cysts

• Chromidial bodies and bars are semicrystalline arrays of riobosomes

Round (10- 16 m), 4 nuclei 150 nm cyst wall with fibrillar

structure Impermeable cyst wall is

responsible for chlorine restistence

Entamoeba cysts (light microscopy)

E. coli E. histolytica

E. histolytica trophozoites and cysts

Right:

E. histolytica

trophozoites

(trichrome stain)

Right:

E. histolytica cysts

iodine (L); trichrome (R)

(Ingested red blood cells)

E. histolytica pathology/clinical symptoms

• worldwide with infection rates ~50% in endemic areas such as C. & S. America, Africa, Asia.

• 90% of patients are asymptomatic contributing to the spread of disease. Long term infection will result in pathogenesis. Damage may go unnoticed for some period of time. Trophs are responsible for all pathology.

• E. histolytica usually is a benign gut commensal as many other amoebae. A certain stimulus (gut flora, diet, host immune status …) transforms the organism into a pathogen ↓

E. histolytica pathology/clinical symptoms cont.

Intestinal: may be a single event or recurrent

a)amoebic colitis: cramps with alternation between loose stool and constipation

b)dysentery: infected patients - hydrolytic enzymes penetrate small hole or ulcer in mucosa, reaches musculature & spreads laterally causing significant undercutting = severe pain, sloughing of mucosa blood & mucus in watery stools, “tear drop” or “flask-like” intestinal lesions.

↓

Colitis is the most common form of disease associated with amoebae

• Amoeba invade mucosa and erode through laminia propria causing characterisitic flask shaped ulcers contained by muscularis

E. histolytica pathology continued

• extraintestinal: Trophs perforate bowel causing peritonitis, and travel to other organs:

• liver: crater-shaped abcesses on surface of liver with chocolate colored exudate.

• Anemia, weight loss & elevated alkaline phosphatase due to liver damage.

• Abcesses in brain, lung, kidney even more rare

Typical pathology of E. histolytica:

a) flask-shaped abcess in mucosa

b) crater-shaped liver abcess

c) liver abcess damage – tube of “chocolate puss” from abcess

Ulceration can lead to secondary infection and extraintestinal lesions

Complications

amebic liver abscess

intestinal perforation, peritonitis

intestinal hemorrhage

intestinal ameboma

amebic appendicitis

Amebic liver abscess

• Most common complication of

extraintestinal amebiasis• Fast growing abscess filled with debris,

amoebae are found only at borders• Lead symptoms are are right upper

quadrant pain and fever• 30-50% of patients with liver abscess

show also pneumonic involvement• Rupture is again a major thread,

especially rupture into pericardium• Draining abscesses is today only

performed in extreme cases when rupture is feared

• Responds well to chemotherapy

Diagnosis:

stool examination - for trophozoites and cysts

amoebic serology abscess aspirate Antigen capture and PCR tests can

distinguish E. dispar from E. histolytica in heavier infections.            

FLAGELLATES

•These organisms have more than one flagellum. These flagella enable them to move. •Flagellates inhabit reproductive tract, alimentary canal, tissue sites, blood stream, lymph vessels and cerebrospinal canal

•Imp spp Giardia lamblia

Distribution: Worldwide, more common in hot climates than temporal regions

Habitat: Upper portions of small intestine. The disease is called Giardiasis (malabsorbtion syndrome)

Morphology• G. lamblia has two morphological

stages: the trophozoite and the cyst.

• Trophozoite: pear shaped, with a broad anterior

10-12µm long and 5-7µm wide

It is also relatively flattened, with a large sucking disk on the anterior ventral side, which serves as the parasite’s method of attachment to the mucosa of the host.

The trophozoite also has two median bodies and four pairs of flagella (anterior, caudal, posterior and ventral)

Cyst:• egg-shaped, and measures 8-

14µm by 7-10µm • After encystation, each

organelle duplicates, so each cyst contains four nuclei, four median bodies, eight pairs of flagella--although these organelles are not arraigned in any clear pattern. Upon excystation, each cyst produces two trophozoites.

• The flagella and adhesive disk are lost as the cyst matures but median bodies and axoneme persist.

Giardia Life Cycle

Pathogenesis• The clinical features associated with Giardia

infection range from total latency (ie, asymptomatic), to acute self-resolving diarrhea, to chronic syndromes associated with nutritional disorders, weight loss and failure to thrive.

• The specific mechanisms of Giardia pathogenesis leading to diarrhea and intestinal malabsorption are not completely understood and no specific virulence factors have been identified.

• Attachment of trophozoites to the brush border could produce a mechanical irritation or mucosal injury.

• In addition, normal villus structure is affected in some patients. For example, villus atrophy and crypt cell hypertrophy and an increase in crypt depth have been observed to varying degrees..

• Giardia infection can also lead to lactase deficiency as well as other enzyme deficiencies in the microvilli.

• This reduced digestion and absorption of solutes may lead to an osmotic diarrhea.

Clinical signsThe clinical features associated with Giardiasis range from total latency (ie, asymptomatic), to acute self-resolving diarrhea, to chronic syndromes associated with nutritional disorders, weight loss and failure to thrive.

Children exhibit clinical symptoms more frequently that adults and subsequent infections tend to be less severe than initial infections. The incubation period is generally 1-2 weeks, but ranges of 1-75 days have been reported.

• Anorexia, nausea, and epigastric uneasiness are additional frequent complaints during chronic infections. In the majority of chronic cases the parasites and symptoms spontaneously disappear. DiagnosisStool Examination:

Stool examination is the preferred method for Giardia diagnosis. Diagnosis is confirmed by finding cysts or trophozoites in feces.

Serology /ELISA to detect IgM in serum provides evidences of current infection