Malarial Parasite – Part 1 – Malaria parasite, Plasmodium Life Cycle And Diagnosis

Sample

1. Malarial parasite (MP) may be diagnosed from a blood smear of a patient with a fever.
   1. The best time to make a smear is during shivering.
   2. Make thick and thin blood smears.
2. Serum needed for a Serological method and for PCR.

Indication

• The diagnosis of the malarial parasite.

Parasitology

1. This word malaria is the Italian word means mala, aria means bad air.
2. The plasmodium grows in the swamp bred mosquito.
3. Malaria is caused by protozoan parasites called Plasmodia and belonging to the Plasmodiidae family.
4. Types of malaria parasites are :
   1. P. falciparum.
   2. P. vivax.
   3. P. ovale.
   4. P. malariae.
   5. A fifth one, P. knowlesi.

5. Vector:

   1. 1. All the Plasmodium species causing malaria in humans are transmitted by mosquito species of the genus Anopheles.
         

         Malarial parasite life cycle

6. Spread:

   1. Sporozoites from the saliva of a biting female mosquito are transmitted to either the blood or the lymphatic system of the recipient.
   2. Malaria spreads through:
      1. Mosquito bite.
      2. Transfusion malaria from the contaminated transfused blood.
      3. By sharing contaminated needle and syringes mostly in the drug abusers.
      4. Congenital malaria is rare.

Plasmodium different shapes are discussed before starting the actual life cycle.

1. Ring form is early trophozoites.
   1. 1. 1. This is a ring-like malarial parasite following the invasion of RBCs.
         2. Giemsa stain shows it as a blue stain cytoplasmic circle connected to a red chromatin dot.
         3. The space inside the ring is known as the vacuole.

2. Trophozoites: The shape varies according to the type of malarial parasite.
   1. 1. 1. There are a cytoplasmic circle and the chromatin dot.
         2. More space is taken by the developing trophozoites.
         3. Pigments are brown in color.

3. Immature schizonts: There is active chromatin replication.
   1. 1. 1. Visible cytoplasmic material surrounds the growing chromatin.
         2. Pigments are often brown.
         3. It occupies more space in the RBC.

4. Mature Schizonts: These are characterized by the presence of merozoites.

5. Microgametocytes: In Plasmodium falciparum is crescent-shaped, in others is typical to a round shape.
   1. 1. 1. There is a large diffuse chromatin mass which stains pink to purple.
         2. Chromatin mass is surrounded by colorless to pale halo.
         3. Pigments are usually visible.

6. Macrogametes: These are round to oval in shape with the exception of P.falciparum which is the crescent shape.
   1. 1. 1. Chromatin is surrounded partially or completely by the cytoplasm.
         2. Pigments are also present.

Lifecycle:

1. Asexual cycle:
2. The majority of sporozoites migrate to the liver and invade hepatocytes.
   1. Initially, elongated sporozoite has transformed into a rounded form.
   2. This rounded form then matures within the hepatocyte to a schizont containing many merozoites.
   3. This cycle takes 5 to 16 days.
   4. Merozoites leave the liver and enter the blood, this is an asexual cycle.
3. The sexual cycle:
4. It starts when the mosquito sucks the blood from the patients.
   1. Micro and macrogametocytes in the stomach of mosquito combine and form zygote.
   2. This forms oocyst and sporozoites.
   3. Sporozoites are injected into humans containing merozoites.

RBCs cycle (Erythrocytic cycle) Asexual cycle:

1. Now Merozoites enter the RBCs and start the Asexual cycle.
   1. produce more merozoites. This cycle repeats 1 to 3 days.
   2. This multiplication can result in thousands of parasite-infected cells in the host bloodstream.
   3. The patient may develop signs and symptoms of illness and complications of malaria.
   4. The complication of the malaria parasite if not treated then it may last for months.
   5. Some of the merozoites transform into a sexual form called as male and female gametocytes.
   6. These gametocytes circulate in the blood are taken up by the biting mosquito.

The life cycle in the mosquito (Sexual cycle):

1. When the mosquito bites the infected humans, then suck the blood and these gametocytes go into along the blood.
   1. In mosquito RBCs, burst and gametocytes are released These will get into more mature form Gametes.
   2. Male and female gametes fuse to form diploid zygotes.
   3. Zygotes develop into actively moving ookinetes that burrow into the mosquito midgut wall and form oocysts.
   4.  Growth and division of each oocyst produce thousands of active haploid forms called sporozoites.
   5.  After 8-15 days, the oocyst bursts, releasing sporozoites into the body cavity of the mosquito, from which they travel to and invade the mosquito salivary glands.
   6. Mosquito is ready to infect humans.
      

      Malarial parasite, mosquito sexual cycle

      

      MP Sexual Asexual Cycle

Clinical presentation

1. The Typical patient is initially asymptomatic following the mosquito bite.
2. Once the erythrocytic phase starts there is a large number of RBCs rupture, leading to the release of merozoites and toxic material.
   1. This is the time when patients get the first attack of malaria as:
      1. First chills for 10 to 15 minutes and then fever 2 to 6 hours or more.
      2. When the fever settles to normal then the patient gets profuse sweating.
      3. This cycle may vary with the type of malaria.
3. The patient may have a headache, lethargy, anorexia, nausea, and vomiting.
4. There may be diarrhea.
5. There is anemia.
6. There may be involvement of the central nervous system.
7. Kidney involvement may lead to nephrotic syndrome.

Complications of Malaria

1. The patient may have :
2. Cerebral malaria.
3. Anemia.
4. Organ failure.
5. Some patients may have respiratory difficulty.
6. Rarely there may be low blood sugar levels.

Diagnosis

1. History of the patient in suspected areas.
2. Blood smear:
   1. Make a blood smear when the patient has a fever. Thin and Thick smears are made.
   2. The thick smear is more helpful to find M.Parasites.
      1. The thin smear is good to identify the type of malarial parasite.
   3. Collect blood 6 to 8 hourly till 48 hours to declare negative for malaria.
   4. Giemsa stain is the best choice.
3. Serologic methods are based on immunochromatic techniques. Tests most often use a dipstick or cassette format and provide results in 2-15 minutes.
4. Polymerase chain reaction (PCR): Parasite nucleic acids are detected using the PCR technique. This is more sensitive than smear microscopy. This is of limited value for the diagnosis of acutely ill patients because of the time needed for this procedure.    

Mosquito control

1. Try to eliminate breeding places:
   1. Fill the vacant land and pump out the water.
   2. Remove the junk and water retaining debris.
2. Destroy the larvae:
   1. Clean the drains.
   2. Try to remove algae from the ponds.
   3. Add larva-eating fish to the ponds.
3. Use of the insecticide:
   1. The best example is DDT.
4. Use of mosquito repellent:
   1. Pyrethroid repellent.
   2. N, N- diethyl meta tolbutamide.
5. Use of mosquito nets.
6. Use of clothes to prevent mosquito bites.
7. Train people for malaria prevalence.
8. Train the people for the detection of malaria, treatment, and follow-up.

Prevention

1. No vaccine is available.
2. Give prophylactic anti-malarial drugs.
3. Use a mosquito net.
4. Use mosquito repellant.

Treatment

1.  Antimalarial drugs used are quinidine, chloroquine, primaquine, pyrimethamine, sulfadoxine, mefloquine, tetracyclines, and proguanil.
2. Chloroquine is the drug of choice and best for P. falciparum.
   1. This is effective for the erythrocytic stage and not for the liver stage.
   2. Must use primaquine to eradicate P. ovale and P. vivax.
   3. there are chloroquine resistant cases of P. falciparum.
3. Amodiaquin, piperaquin and pyronaridine are close to chloroquin.
   1. Amodiaquine is less toxic, cheap, and in some areas effective against chloroquine-resistant P. falciparum.
4. Mefloquine is effective against choloquin resistant P. falciparum.
5. Quinine and quinidine are still the first line of therapy against P.falciparum.
6. Primaquine is a synthetic drug and is the drug of choice for the eradication of liver-stage from P. vivax and P. ovale.
7. Antibiotics and Inhibitors of folate synthesis are slow-acting antimalarial drugs.
8. Halofantrine and Lumefantrine are related to quinine and effective against the erythrocytic stage.
9. Malaria drug-resistant strains are emerging.                              

Characteristic features of  various forms of the Malarial parasite 

Malaria type	Stages	Infected RBC size	Trophozoite	Scuffer stippling	GAMETOCYTES	Pigments (hematin)	Schizont nuclei
P. vivax	All	enlarged	small and may become amoeboid	present	rounded	light brown	12 to 24
P. Ovale	All	enlarged	small, with large chromatin	present	rounded	dark brown	6 to 12
P. malariae	All	normal	small with dense cytoplasm, rarely band form	absent	rounded	dark brown	6 to 12
P. falciparum	ring form	normal	smallest, sometimes multiple, often double chromatins	absent	banana-shaped	black	rarely

 Typical features of Malarial parasite

	P. falciparum	P. vivax	P. ovale	P. malariae
Incubation period	8 to 11 days	7 to 10 days	7 to 10 days	18 to 40 days
Fever pattern	Continuous, quotidian, or remittent	Irregular or quotidian	Irregular or quotidian	usually regular after 72 hours.
Prodromal symptoms	Influenza-like	Influenza-like	Influenza-like	Influenza-like
The periodicity of symptoms	36 to 48 hours	44 to 48 hours	48 to 50 hours	72 hours
The severity of the initial attack	Severe 16 to 36 hours	moderate to severe, 10 hours	mild for 10 hours	moderate to severe 11 hours
Duration without treatment	2 to 3 weeks	3 to 8 + weeks	2 to 3 weeks	3 to 24 weeks
CNS involvement	very severe  ++++	±	±	±
Anemia	very severe ++++	++	+	++
Kidney involvement	+	±	–	+++
Red blood cell	normal size	larger than the normal, Schuffner’s dots are seen	larger than the normal, schuffner’s dots are often seen	about normal or  slightly smaller
Early trophozoite	about 1/5 diameter of RBC, chromatin is a small dot	about 1/3 diameter of RBC with heavy chromatin dots	Like vivax and malariae	single, heavy chromatin dot
Trophozoite mature	usually not seen in peripheral blood	as a large mass of chromatin, fine brown pigments		Chromatin is elongated and less definite.
Schizont	8 to 24 or more merozoites	12 to 24 merozoites	4 to 16 but more common 8 merozoites	6 to 12 but usually 8 or 10 merozoites
Macrogametocyte	size like microgametocyte. chromatin more compact	Cytoplasm stains dark blue, chromatin more compact		Abundant pigments and coarser, dark brown granules
Microgametocyte	Crescent-shaped, chromatin is diffuse, pink, cytoplasm pale blue	Round or oval, almost fill the RBC, chromatin is diffuse in large masses, pink, no vacuoles	Like vivax but smaller	like vivax but smaller and pigments more prominent
Stages development in the mosquito	10 to 12 days at 27 °C	10 days at 25 °C  to 30 °C	14 days at 27 °C	25 to 28 days at 24 °C

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