Malarial Parasite in the Blood

Introduction

Malaria is an infectious disease caused by the parasite called Plasmodia. There are four identified species of this parasite causing human malaria, namely, Plasmodium vivax, P. falciparum, P. ovale and P. malariae. It is transmitted by the female anopheles mosquito scientifically known as Anopheles minimus flavirostris. It is re-emerging as the # 1 Infectious Killer and it is the Number 1 Priority Tropical Disease of the World Health Organization.

Malaria- A Major Global Health Problem

• Malaria affects more than 2400 million people, over 40% of the world's population, in more than 100 countries in the tropics from South America to the Indian peninsula. The tropics provide ideal breeding and living conditions for the anopheles mosquito, and hence this distribution.

• Every year 300 million to 500 million people suffer from this disease (90% of them in sub-Saharan Africa, two thirds of the remaining cases occur in six countries- India, Brazil, Sri Lanka, Vietnam, Colombia and Solomon Islands).

• WHO forecasts a 16% growth in malaria cases annually.

• About 1.5 million to 3 million people die of malaria every year (85% of these occur in Africa), accounting for about 4-5% of all fatalities in the world.

• One child dies of malaria somewhere in Africa every 20 sec., and there is one malarial death every 12 sec somewhere in the world.

• Malaria kills in 1 year what AIDS killed in 15 years. In 15 years, if 5 million have died of AIDS, 50 million have died of malaria.

~* GENUS *~

• The malarial parasites of humans are caused by species of the genus Plasmodium of the class Sporozoa.

• The asexual cycle (schizogony) takes place in the red blood cells of vertebrates and the sexual cycle (sporogony) in mosquitoes.

•he members of this genus, which cause malaria in mammals and birds, have closely similar morphology and life cycles.

~* LIFE CYCLE *~

• The life of the plasmodia is passed in two hosts, a vertebrate and a mosquito.

• The asexual cycle in the vertebrate host is known as schizogony, and the sporulating sexual cycle in the mosquito as sporogony.

Life Cycle of Plasmodia

Detailed Life Cycle of Plasmodium

Life Cycle of Plasmodia

Life Cycle of Plasmodia

P. vivax P. malariae P. falciparum P. ovale

Other names

Benign tertian

Quartan Malignant tertian aestivo-

autumnal

Benign tertian or

ovale

Incubation period (days)

14 (8 – 27) 15 - 30 12 (8 – 25) 15 (9 – 17)

Persistent EE stages

Yes No No Yes

Parasitemia (mm3) Average Minimum

20,00050,000

6,00020,000

50,000 - 500,000

Up to 2,500,000

9,00030,000

Duration of untreated infection (years)

1.5 – 4.0 1.0 – 30 0.5 – 2.0 Probably 1.5 – 4.0

~* CLINICAL DIFFERENTIATION OF THE MALARIAS *~

~* DISEASES *~

• Malaria, are known by several names among which are paludism, intermittent fever, chills and fever, Roman fever, Chagres fever, marsh fever, tropical fever, coastal fever and ague.

• The term malaria is derived from two Italian words, mal (bad) and aria (air).

~* Species Pathogenic to Man *~

• P. malariae was described in 1880 by Laveran.

~ has an affinity for mature or older red cells

• P. vivax was named in 1890 by Grassi and Feletti.

~ prefer to invade young red cells

• P. falciparum in 1897 by Welch.

~ infects cells of all ages

• P. ovale in 1922 by Stephens.

~ prefer to invade young red cells

~* MORPHOLOGY *~

• Some general characteristics are common to all malaria parasites, but differential features make it possible to identify species.

• The earliest form after invasion of the re blood cell is a ring of bluish cytoplasm with a dot-like nucleus of red chromatin.

• As this early stage, the trophozoite, grows the erythrocyte hemoglobin is metabolized to produce a darkly staining malarial pigment, hemozoin.

• Depending upon the species of parasite, the cytoplasm may become irregular in shape, and the red blood cell may show pink granules.

• When the growing parasite divide, it is called a schizont, showing multiple masses of nuclear chromatin.

• Some of the trophozoites develop into gametocytes, or sexual stages, which are differentiated by compact cytoplasm and the absence of nuclear division.

~* PLASMODIUM VIVAX *~

• The infected red cell is enlarged, but this may be partly explained by the affinity of the parasite for larger reticulocytes.

• As the signet-ring appearing trophozoite grows, it becomes irregular in shape, with amoeboid extensions of the cytoplasm.

• Schuffner’s dots make their appearance in properly stained smears of P. vivax infected cells; these are fine, round, pink or reddish granules, distributed uniformly over the red cell.

• Increasing amounts of the of pigment accumulate in the parasite cytoplasm.

• After 36 hours, the parasite fills over half the enlarged red cell, and the nucleus divides, becoming a schizont.

• By 48 hours the schizont has segmented into 16 distinct cells, the merozoites, each with a red nucleus and blue cytoplasm condensed about it. And the rupture of the erythrocyte takes place.

• The gametocytes resemble a late trophozoite prior to segmentation.

• They are oval, nearly filling the red cell – the microgametocyte with less deeply staining nucleus and cytoplasm, the macrogametocyte with darker blue cytoplasm and more compact nucleus.

RING RING RING RING

TROPH TROPH TROPH TROPH

AMOEBOID SCHIZONT SCHIZONT SCHIZONT

SCHIZONT IMMATURE SCHIZONT MATURE SCHIZONT

GAMETOCYTE GAMETOCYTE

GAMETOCYTE FEMALE GAMETOCYTE MALE GAMETOCYTE

~* PLASMODIUM MALARIAE *~

• The early ring form of P. malariae resembles that of P.vivax, but the parasite is smaller, less irregular, and more compact, the cytoplasm is a deeper blue.

• The growing trophozite acquires coarse granules of dark brown or black pigment and may assume a band shape across the cell.

• Infected red cells are normal or even smaller than most in size since old cells are preferentially infected.

• A period of 72 hours is required for the development of the mature schizont, which resembles a daisy or rosette with only eight to ten oval merozoites.

• A compact mass of greenish black pigment is often located centrally, surrounded by merozoites.

• The gametocytes are similar to those of P. vivax but are smaller.

RING TROPH TROPH COMPACT TROPH

BAND FORM IMMATURE SCHIZONT MATURE SCHIZONT SCHIZONT

SCHIZONT SCHIZONT SCHIZONT FEMALE GAMETOCYTE

GAMETOCYTE GAMETOCYTE

~* PLASMODIUM FALCIPARUM *~

• This differs from other plasmodia of humans in that, except in infections with very high parasitemia, only in the ring forms of early trophozoites and the gametocytes are ordinarily seen in the peripheral blood.

• Schizogony takes place in the capillaries of the muscles and viscera, and very few schizont are found in the peripheral blood.

• The infected red blood cells are of normal size.

• The presence of more than one ring form in a cell is relatively common.

• Double chromatin dots are frequently found in P. falciparum ring forms, and only occasionally in the rings of other species.

• The schizonts, seldom found in the blood, resemble those of P. vivax but have smaller and a few more merozoites when mature and ready to rupture.

• The immature gametocytes gradually acquire an elliptical shape, stretching but remaining within the red cell.

• When fully developed, they have a characteristic banana shape, the so-called crescent.

• In cells, infected with P. falciparum there are sometimes cytoplasmic precipitates known as Maurer’s dots that appear as irregularly distributed red spots or clefts.

APPLIQUE FORM DOUBLE RING MULTIPLE RING

OLD RING RING TROPHOZOITES

MATURE SCHIZONT GAMETOCYTE MALE GAMETOCYTES

THICK FILM EXFLAGELLATION

~* PLASMODIUM OVALE *~

• Commonly found in West Africa, but infrequently encountered elsewhere, is similar to P. vivax and P. malariae in several characteristics.

• The infected red blood cells are slightly enlarged, can be of oval shape, and show Schuffner’s dots.

• An important diagnostic feature is the irregular or fimbriated appearance of the edges of the infected red cell.

• Schizonts have centrally massed pigment and only about eight merozoites when mature.

RING RING RING

TROPH TROPH TROPH

SCHIZONT SCHIZONT MATURE SCHIZONT

GAMETOCYTE GAMETOCYTE GAMETOCYTE