PH  172  –  Introduction to Protozoans, Plasmodium    February  11,  2013   Prof.  Rivera  

PL,  Liana,  RJ,  Laine,  Jo   1  of  4  

PROTOZOA • Unicellular • Organelles: (We use this to classify the protozoans, as

opposed to using the reproductive system for helminth classification) o Nucleus – most important structure used to

differentiate species – stain eosinophilic – can be easily differentiated

o Karyosome – stain eosinophilic; – can be easily differentiated

o Kinetoplast – made up of DNA – located very near flagellum

o locomotory organelles – the basis of classification Visible under light microscope

• pseudopodia: crawling motion • flagella: falling leaf motion • cilia:rotatory or very rapid motion

Visible under electron microscope • Apical complex: invasive organelles of

AP complexa/sporozoans • Mitochondria, ER, ribosomes, golgi

complex

PLASMODIUM • The Malaria Parasites • Behaves like bacteria or viruses • “Mala aria” – bad air • People associated fever with bad-smelling water

(stagnant water where mosquitoes breed) However, anopheles (vector mosquito for malaria) does not breed in stagnant water (unlike the vector for Dengue)

• Is different with the parasites we’ve discussed in the sense that it multiplies (and divides) inside the body (behaves like bacteria and viruses). So that instead of reduced adult stage compared to the infective stage, it multiplies inside the body.

MALARIA : all about schizogony and the resulting destruction of RBCs Life Cycle

Ø Intermediate host: MAN Ø Definitive host: MOSQUITO (Anopheles) Ø Infective stage: Sporozoites Ø Diagnostic stage: Merozoites in blood Ø Mode of transmission: mosquito bite, blood

transfusion, infected mother can transmit to the fetus in vitro through shared needle use (drug users) • not by drinking/ swimming etc in contaminated

water

PREERYTHROCYTIC CYCLE [“before the red blood cell”]

1. During blood meal, malaria-infected female Anopheles mosquito inoculates sporozoites into human

2. Sporozoite (infective stage) invades hepatocyte (liver cells) and develop into schizonts

3. It divides by exo-erythrocytic schizogony • asexual reproduction

(some become hypnozoites – remain in liver and become inactive, found only in P. ovale and P. vivax: causes malaria relapse even w/o the mosquito bite)

4. Schizont in hepatocyte ruptures to release merozoites *after this initial replication in the liver called exo-erythrocytic schizogony, parasites undergo asexual multiplication in the erythrocytes (erythrocytic schizogony) discussed below

ERYTHROCYTIC CYCLE

5. Merozoites invades RBCs and multiplies by schizogony and produces many more merozoites

6. RBCs rupture, releasing merozoites that invade more red blood cells

7. Some of the released merozoites differentiate into macrogametocytes (female erythrocytes) and microgametocytes (male erythrocytes), the sexual stages *The blood-stage parasites are responsible for the clinical manifestations of the disease

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IN MOSQUITO (EXOERYTHROCYTIC) 8. Mosquito takes these gametocytes in through a blood

meal 9. While in the mosquito's stomach, the microgametes

penetrate the macrogametes generating zygotes 10. Zygotes become motile and elongated and become

ookinetes 11. These invade midgut of mosquito and undergoes

fertilization in the midgut wall of the mosquito to develop into oocysts

12. The oocysts grow, rupture and releases sporozoites 13. They then undergo sporogony 14. The sporozoites migrate to the salivary gland of the

mosquito 15. Sporozoites are inoculated into human host through

blood meal *The parasites’ multiplication in the mosquito is known as the sporogonic cycle

THE DIFFERENT PLASMODIUM SPECIES

Plasmodium falciparum • most VIRULENT species because all stages of the RBC are

infected • most common species

1. Ring forms (the trophozoite stage) § Very small § usually w/ 2 nuclei,

accole, > 1 ring form can be found in 1 RBC (multiple infection)

§ “applique” – rings are found on periphery of RBC

§ RBCs look normal except for the ring forms

2. Cresent or banana shaped gametocytes

3. Schizonts

• Rarely seen • 8-32 merozoites • Means bad prognosis

because this can only seen in complicated & bad malaria cases

Plasmodium vivax • 2nd most common species • Main difference with with Plasmodium falciparum:

• Enlarged RBC • Presence of Schuffner’s dots (found in the enlarged

RBCs)

1. Ring forms • occupies 1/3 of the

diameter of RBC • Trophozoite – amoeboid or

irregularly shaped

2. Round or ovoid gametocytes

[28: developing macrogametocyte, 29: mature macrogametocyte

(female), 30: mature microgametocyte (male)]

3. Schizonts • 8 – 24 merozoites

Plasmodium malariae • Not as common as the other two • Normal size RBC (no enlargement)

1. Ring forms • occupies at least 1/3 of the diameter of RBC • Trophozoite: basket or band form

[left: ring form, middle: basket form trophozoite, right: band form

trophozoite]

2. Ovoid gametocytes

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3. Schizonts • 8 – 12 merozoites in “rosette formation”

Plasmodium ovale • Name is derived from the change of RBC into an ovalocyte

(oval in shape) • Presence of Schuffner’s dots in cytoplasm (can be

observed w/ proper staining) • Not present in the Philippines but common in Africa

1. Ring forms

[far right: trophozoite w/ fimbriation and Schuffner’s dots]

2. Gametocytes

[left: microgametocyte w/ Shuffner’s dots (note the oval shape),

right: macrogametocyte w/ fimbriation]

3. Schizonts

Plasmodium knowlesi Ø In monkeys, but known to jump from monkeys to man Ø Causes severe hemolysis and even death Ø In Sarawak, Malaysia

• Symptoms (non-specific) that precede the actual paroxysm:

§ Lassitude (feeling weak), headache, nausea, anorexia, chilly sensation, low grade fever, etc.

Malaria Paroxysms

• Periodic & sequential attacks of chills, fever and sweating o Increase in temperature caused by schizogony

because of the natural response of the body to kill microorganisms

o Lymphocytes, sperm cells, ova – also killed by the increase in temp, so the body lowers the temp by sweating

• Related to periodic destruction of infected RBCs which induce fever and subsequent invasion of normal RBCs by parasites

Periodicity varies according to species: Plasmodium falciparum

36-48 hours Malignant tertian (every 3rd day)

Plasmodium vivax

48 hours Benign tertian (every 3rd day)

Plasmodium malariae

72 hours Quartan (every 4th day)

Plasmodium ovale

48 hours Benign tertian (every 3rd day)

Periodicity is usually not apparent during the first days of the attack because the cycle is not yet synchronous. Other Signs and Symptoms of Uncomplicated Malaria

• Headache, body pain, anorexia, nausea, vomiting, abdominal pain, pallor, enlarged and tender spleen, and sometimes cough

• There must be a high index of suspicion to diagnose malaria using these symptoms o Visiting or resident of an endemic area

PATHOGENESIS

AT THE MOLECULAR LEVEL

• Proteins are expressed on the surface of the RBC o PfHRP 1, PfEMP 1, PfEMP 2, PfEMP 3

(adherence proteins à cause schizont to adhere to the endothelial capillaries and endothelial cell receptors ICAM-1, VCAM-1, E-selectin P-selectin, trombospondin, CD36, CD31, chondroitin sulfate)

Ø Cytoadherence to vital organs can cause obstruction of

blood flow which may cause anoxia and death of cells Ø Death can be caused by multiple organ involvement Ø Severe anemia: more common in children and pregnant

women § Very low hemoglobin levels (< 5; or 1/3 of normal)

PRODROMAL  SYMPTOMS  

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Ø Pulmonary edema: life threatening condition § Medical emergency § In P. falciparum infections

Ø Cerebral malaria § Ring forms, schizonts, and cytoadherence in the brain § Very few with this condition recover

Severe malaria is defined by WHO (1990) as asexual parasitemia with one or more of these manifestations:

• Severe anemia • Impaired consciousness • Poor urine output • Pulmonary edema/ARDS • Prostration • Macroscopic hemoglobinuria • Jaundice • Seizures • Hyperpyrexia (rectal temp > 40C) • Hyperparasitemia (>5% parasitized RBC, >106

asexual parasites/mm3 blood) • Disseminated intravascular coagulation • Metabolic abN (acidosis, hypoglycemia)

EARLY DIAGNOSIS & TREATMENT is needed for Malaria! (to

be discussed next week)

All photos were taken from the CDC site “DPDx” If you want to see more photos, just visit this link and select the

Plasmodium species that you would like to see pics of. http://www.dpd.cdc.gov/dpdx/HTML/ImageLibrary

/Malaria_il.htm

This will probably help with the lab blood unknown J

And because Valentine’s Day is this week…