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ByA.S.ARUL LAWRENCE

Principal, St.Joseph College of Education,Nanguneri-627108, Tamil Nadu.

E-mail : arullawrence@gmail.com.

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Causal Agents:

• Blood parasites of the genus Plasmodium. 

• There are approximately 156 named species of Plasmodium which infect various species of vertebrates. 

• Four are known to infect humans: P. falciparum, P. vivax , P. ovale  and P. malariae.

 

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What is a Malarial Parasite?The malarial parasite, Plasmodium, is a

very small, single-cell blood organism, or 'protozoan'.

It lives as a parasite in other organisms, namely man and mosquito. The parasite is the cause of the tropical disease Malaria.

The Plasmodium parasite is dependent on a single species of mosquito, Anopheles, which is the only species capable of serving as host for it.

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Male & Female Plasmodium.

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Classification Phylum : Protozoa Sub- Phylum : Sporozoa Class : Telosporea Sub-Class : Coccidia Order : Eucoccida Sub-Order : Hamosporidiidea Family : Plasmodiidae Genus : Plasmodium

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Worldwide, malaria usually restricted to tropical and subtropical areas and altitudes below 1,500 m.

P. vivax is more common in Central America and the Indian subcontinent

Geographic Distribution.

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Infection rate. WHO estimates that yearly 300-500

million cases of malaria occur and more than 1 million people die of malaria.

P. vivax and P. falciparum are the most common.

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Mode of Infection.

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Vector & Parasite.

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Life cycle. A malaria-infected female Anopheles

mosquito inoculates sporozoites into the human host during a blood meal.

Sporozoites infect liver cells and mature into schizonts, which rupture and release merozoites (exo-erythrocytic schizogony).

In P. vivax and P. ovale a dormant stage (hypnozoites) can persist in the liver for weeks, or even years. The merozoites infect red blood cells.

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Life cycle…

• The ring stage trophozoites mature into schizonts, which rupture releasing merozoites (erythrocytic schizogony).

• Some parasites differentiate into sexual erythrocytic stages (gametocytes).

• The gametocytes are ingested by an Anopheles mosquito during a blood meal.

• The microgametes penetrate the macrogametes generating zygotes in the mosquito's stomach.

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Life cycle…..

• The zygotes become ookinetes and invade the midgut wall where they develop into oocysts.

• The oocysts grow, rupture, and release sporozoites, which make their way to the mosquito's salivary glands (sporogonic cycle).

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Sporozoite Invasion.

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Erythrocytic Schizoite.

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Amoeboid Stage.

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Ring Stage.

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Male Gamete.

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Female Gamete.

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Fertilization.

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Mature Oocyst.

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Rupturing of Oocyst.

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MALARIAL PARASITE’S DIFFERENT CYCLES

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Sickle cell anaemia and malaria A genetic disorder, called sickle cell anaemia, happens

when a person inherits two faulty genes to make the haemoglobin in their red blood cells which then break open and cause serious damage due to blood clots.

Carriers who possess one faulty haemoglobin gene and one normal gene do not suffer from anaemia but are found to have some protection against infection by the malaria parasite.

In areas where malaria is common, the amount of sickle cell carriers is higher than in other parts of the world.

In an unusual example of Darwin's principle of survival of the fittest, carriers of the genetic disorder are actually more likely to survive than people with two unaffected genes for haemoglobin.

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Species Plasmodium vivax Plasmodium ovale

Plasmodium malaria

ePlasmodium

falciparum

Pre-erythrocytic cycle (days)1 8 9 13 5.5-6

Pre-patent period (days)2 11-13 10-14 15-16 9-10

Incubation period (days)3 13 (12-17) or up to 6-12 months

17 (16-18) or

longer

28 (18-40) or

longer12 (9-14)

Exo-erythrocytic cycle (secondary)4 Present PresentPresent in

some strains?

Absent

Approximate number of merozoites per tissue schizont Over 10,000 15,000 2000 40,000

Erythrocytic cycle (hours)5 48 49-50 72 48

Parasitemia (per l (mm3) Average 20,000 9000 6000 20,000-500,000

Maximum 50,000 30,000 20,000 2,000,000

Primary attack severity Mild to severe Mild Mild Severe in non-immunes

Febrile paroxysm (hours)6 8-12 8-12 8-10 16-36 or longer

Relapses ++ ++ +++ -

Period of recurrence7 Long Long Very long Short

Duration of infection (years) 1.5-3 1.5-3 3-50 1-2

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1. Vivax malaria

2. Tertian malaria

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Symptoms: The most frequent symptoms include fever

and chills, which can be accompanied by headache, myalgias, arthralgias, weakness, vomiting, and diarrhea. 

Other clinical features include splenomegaly, anemia, thrombocytopenia, hypoglycemia, pulmonary or renal dysfunction, and neurological changes. 

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Laboratory Diagnosis: Microscopy Microscopic identification is

the method most frequently used to demonstrate an active infection.

Comparison of Plasmodium species Molecular diagnosis techniques can

complement microscopy, especially in species identification.

Antibody Detection can detect past (not necessarily active) infections.

Immunologic/Biochemical detection of malaria parasite products are available and under evaluation

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Treatment: • Treatment varies according to the

infecting species, the geographic area where the infection was acquired, and the severity of the disease. 

• A complete guide for treatment of malaria can be found in The Medical Letter (Drugs for Parasitic Infections), as well as on the Division of Parasitic Diseases Web site.

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Prevention.• Personal protection against

mosquito bites is the first line of defence against malaria.

• In addition, travellers should take chemoprophylaxis where appropriate

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