9_Medically Important Protozoans

Protozoa

• are one-celled animals found worldwide in most habitats

• Unicellular eukaryotes

• Size range from 1 to more than 100 um.

• Heterotrophs; some anaerobes

• Lives in area with large supply of water

• Takes food across membrane; if with pellicle covering, take food thru cytostome

• Digest food in vacuoles; expel waste thru anal pore

• Has tropozoite (feeding and growing)

• Has cyst stage protected by capsule (a reproductive structure)

• Reproduction is asexual thru fission, budding, or schizogony (multiple fission)

• Multiple karyokinesis followed by concentration of cytoplasm around each, then separation.

• Sexual reproduction by conjugation

genetic chimera

Biologists agree that the eukaryotic cell is a ___

• Mitochondria and chloroplasts contain DNA

• eukaryotic nucleus contains genes derived from Bacteria – nuclear DNA has genes for mito- and chloro

• Organellar ribosomes and their phylogeny.

• Antibiotic specificity – antibiotics inhibitory to mito and chloro

• Hydrogenosomes- membrane-enclosed organelles in amitochondriate eukaryotic anaerobes; has DNA and ribosomes

Endosymbiotic hypothesis (theory) facts:

primary endosymbiosis events

mitochondrion, chloroplast, and hydrogenosome - structures originated from

Secondary endosymbioses

• following this primary event, several unrelated groups of nonphototrophic microbial eukaryotes also acquired chloroplasts by secondary rather than primary endosymbioses.

• occurred when entire green algal or red algal cells were engulfed and their chloroplasts stably retained, making the engulfing cell phototrophic – process of

Trophozoite

Forms of protozoa: vegetative form

Cyst

Forms of protozoa: resting stage marked by presence of cell wall

oocyst

In coccidians,cyst form is ___, in which sporogony occurs

Pellicle

plasma membrane where cilia are attached

Macronucleus

regulates somatic functions (locomaoion, feeding, osmoregulation, cell regeneration) by directing protein synthesis

Micronucleus

functions in sexual reproduction, regeneration of macronucleus

pseudopodia (false feet)

blunt lobe-like extensions of the cytoplasm

flagella

thin, long whip-like projections arising from the surface of the cell

Giardia lamblia

• trophozoite shape of a tennis racket (heart-shaped or pyriform-shaped).

• rounded anteriorly and pointed posteriorly.

• falling leaf-like motility and measures 12-15 µm length and 4µm thick.

• dorsoventrally convex and ventrally, it has a concave sucking disk, which helps in its attachment to the intestinal mucosa. Hence, it appears as sickle-shaped in lateral view.

• bilaterally symmetrical on each side from the midline and it possesses:

• One pair of nuclei

• Four pairs of flagella (two lateral, one ventral, and one caudal pair of flagella)

• One pair of axostyles, running along the midline.

• Two sausage-shaped parabasal or median bodies, lying transversely posterior to the sucking disk

10 cysts

Ingestion of G. lamblia as far as___ are sufficient to cause infection in a man.

antigen

presence of ___ indicates active infection

green glowing ovoid objects

Visualization under a fluorescent microscope shows the Giardia cysts as ___ ,

Plasmodium falciparum

• is the most virulent species of Plasmodium in human (malignant tertian malaria (malaria tropica)

• causes malignant tertian or falciparum malaria

‘falx’

‘falciparum’ is derived by Welch from __meaning sickle or crescent and ‘parere’ meaning to bring forth

sickle or crescent

‘falciparum’ is derived by Welch from ‘falx’ meaning ___ and ‘parere’ meaning to bring forth

‘parere’

‘falciparum’ is derived by Welch from ‘falx’ meaning sickle or crescent and __meaning to bring forth

to bring forth

‘falciparum’ is derived by Welch from ‘falx’ meaning sickle or crescent and ‘parere’ meaning ___

parenchymal cells of liver and inside RBCs of Human

Various stages of malarial parasites are found inside the __

haemozoin

In Plasmodium, a single large mass of pigment colored yellow to black called ___are present.

• Pre-erythrocytic schizogony in liver

• Erythrocytic schizogony and gametogenesis in RBCs

two main stages of development in Plasmodium

Pre-erythrocytic or primary exo erythrocytic schizogony: Liver

two main stages of development in Plasmodium:

• comprises a single cycle and lasts for 6 days.

• 1. Infected mosquitoes during bite inject sporozoites along with saliva into blood vessels.

• 2. motile sporozoites are carried rapidly within 30 minutes to the liver by blood stream.

  • circumsporozoite protein cover of sporozoite binds specifically and non-covalently with receptors on basolateral area of hepatocyte - sporozoites enter into liver cell only.

• 3. in liver cells, sporozoite mature as schizonts (and/or hypnozoites), undergo schizogony to form merozoites (hypnozoites may be dormant for months or years).

  • schizonts are spherical, multinucleated and measures 60µm or more in diameter; contains 2000-30000 uni-nucleated merozoites (daughter cells following asexual reproduction (schizogony).

• 4. Mature schizonts and liver cell ruptures releasing thousands of merozoites into blood stream (after 6 days)

Erythrocytic schizogony

two main stages of development in Plasmodium:

• 5. Merozoites from liver invade erythrocyte and begins erythrocytic schizogony

  • merozoites become attached to the glycoprotein and other sialoprotein receptors of red cell selectively.

  • nature of haemoglobin and red blood cell enzymes influences the development of merozoites inside RBCs. Development of. P. falciparum is suppressed in presence of fetal haemoglobin and also in presence of other few haemoglobin.

• 6. In RBC, merozoites develops into young trophozoites or ring form - feed on haemoglobin by ingesting red cell cytoplasm (less then 12 hrs.).

• 7. Young trophozoites (ring form) develop to become mature schizonts, or another form, the gametocytes.

• 8. Rupture of schizonts (after schizogony) release merozoites into blood circulation and penetrate new RBC and begins new erythrocytic schizogony.

  • As mature schizont is less symmetrical and contains 8-32 merozoites and haemozoin.

  • Erythrocytic schizogony is completed with 48 hours and always take place inside capillaries and vascular layer of internal organs – why P. falciparum usually not demonstrated in peripheral blood smear preparation.

  • Malarial paroxyms as this point.

Gametogenesis in RBC

two main stages of development in Plasmodium:

• After two or three erythrocytic schizogony, some of the merozoites invade new erythrocyte and develop into male and female gametocytes.

• gametocytes develops in RBCs of bone marrow and spleen.

• stimulus for the production of gametocytes - not known, believed to be due to lack of nutrients, accumulation of metabolic or parasitic debris or due to development of immunity.

• gametocytes are crescent shape with haemozoin granules found in the central part of cytoplasm surrounding the nucleus. Only mature gametocytes are found in peripheral blood.

• Gametogenesis completes in 96 hours

Exo-erythrocytic cycle, Erythrocytic cycle, Sporogonic cycle

In Plasmodium, there are 3 cycles

Bite of infected Anopheles mosquito harboring sporozoites • Blood transfusion • Transplacental transmission • Organ transplantation

Mode of transmission: (Plasmodium)

Sequestration

condition of holding back of mature parasites in vital organs.

knobs

• P. falciparum merozoites produces a protein within erythrocyte surface membrane in the form of deformation called __

• produce high molecular weight strain specific adhesive protein

• mediate attachment of to receptors on endothelium of capillaries and veins

RBC, Liver, CNS, kidney, spleen and lungs

Organs infected by Plasmodium malaria

malaria

Infection with P. falciparum caused intermittent fever (day 1, then day 3) called___- meaning bad air

Malarial paroxysm

acute malaria, characterized by fever, chill and rigor.

Cold stage • Hot stage • Sweating stage

Each paroxysm shows a succession of 3 stages

• detection of multiple rings in a single RBC with accole form

• Presence of maurer’s dots in RBC containing large ring

• Presence of characteristics banana shaped gametocyte

Diagnostic of P. falciparum in microscopy