Four species of Plasmodium commonly cause malaria in humans: P. falciparum, P. vivax, P. ovale, and P. malariae. They have complex life cycles that involve sexual reproduction in mosquitos and asexual reproduction in human liver and red blood cells. Symptoms include periodic fevers corresponding to the rupture of infected red blood cells. Diagnosis is via microscopic examination of blood smears to identify the parasitic stages or rapid diagnostic tests to detect parasite antigens.

2. Human malaria
Kingdom : Protista
Subkingdom : Protozoa
Phylum : Apicomplexa
Class : Sporozoasida
Order : Eucoccidiorida
Family : Plasmodiidae
Genus : Plasmomdium
Species : falciparum , malariae , ovale , vivax

3. Causative agents of human malaria :
More than 50 species of plasmodium infect a wide
variety of animals , but only 4 types commonly
cause malaria in humans .
 Plasmodium vivax ( benign tertian )
Plasmodium falciparum ( malignant tertian ) :
is the most pathogenic form of human malaria
and is often fatal unless treated ( is responsible for
almost all deaths caused by malaria ) .
Plasmodium malariae ( Quartan malaria )
Plasmodium ovale ( tertian malaria )

4. Distribution :
P. vivax :
is the predominant malaria in most parts of the world
P. falciparum :
is mostly confined to the tropics and subtropics
P. malariae :
occurs in subtropical and temperate areas . it is less
frequently seen than P. vivax or P. falciparum
P. ovale :
is confined to west Africa . it is the rarest of all plasmodia
infecting humans .

5.  Epidemiology :
 Endemicity of human malaria is determined by the geographic
distribution of its arthropod vectors , Anopheles mosquito .
 Local environmental factors :
 determine which particular species of mosquito transmits malaria in
a given area
 affect breeding and/or sporogony ( These functions require
temperatures between 16 and 34 C and a relative humidity in excess
of 60 % )
 Recently , there have been several infections in people who lived
near or visited airports where flights returned from endemic areas ,
harboring infected mosquitoes
 Critical density :
 Statistical computation of the average number of bites per person
per night yields the critical density
 A continuously declining critical density indicates that malaria in a
survey area is waning and may eventually disappear
 Critical density is influenced by environment factors .

6. Habitat :
- In human , the parasites are found in the erythrocytes and hepatocytes
Vector :
- Human malaria is transmitted by over 60 species of female Anopheles
mosquito .
- Only female mosquitoes serve as vectors . the mouthparts of males
can’t penetrate human skin . females , on the other hand , also feed
on blood , which is usually required for oviposition
( male mosquitoes feed on plant juices )
Life cycle : Malaria parasite complete its life cycle in 2 hosts
1) Its definitive host is the female Anopheles mosquito
2) Human are the intermediate host
Modes of transmission : are via
 bite of infected Anopheles mosquito ,
 blood transfusion , shared syringes , organ transplant , laboratory
accidents & congenital transmission
Infective forms of the parasites are : sporozoites .

7. Life cycle :
A significant feature of the life cycle is the alteration of sexual and
Asexual phases in the two hosts
1.Asexual phase
( in intermediate host )
2. Sexual phase
( in definitive host )
is known as schizogony Is known as sporogony
It occurs in human It occurs in the mosquito
It takes place in :
 in the liver cells
( exo-erythrocytic or
pre-erythrocytic schizogony )
& in the red blood cells
( erythrocytic schizogony )
Maturation and fertilization of
the gametocytes take place in
the mosquito , giving rise to a
large number of sporozoites
( sporogony )

10.  Human cycle ( schizogony ) :
- Human acquire infection from the bites of infective female
Anopheles mosquito
- The sporozoites , which are the infective forms of the parasite , are
present in the salivary gland of the mosquito
- They are injected into blood capillaries when the mosquito takes a
blood meal
These sporozoites circulate in the blood stream and enter the liver
parenchymal cells ( hepatocytes )

11. a) Exo-erythrocytic cycle :
- Within 30 min. , the sporozoites reach the liver and enter the
hepatocytes to initiate the stage of pre-erythrocytic schizogony
- In P. vivax and P. ovale , they form schizont which persist and
remain dormant (hypnozoite)
- From time to time , the dormant schizonts are reactivated and
release merozoites , which go on to infect RBCs causing clinical
relapse
- Once inside the hepatocyte , the sporozoite develops into a
trophozoite , feeding on the host cytoplasm
-After 1 to 2 weeks ( depending on the species of Plasmodium ) ,
multiple division of trophozoites occurs to produce thousands of
merozoites
-The merozoites rupture from the host cell , enter the blood
circulation , and invade red blood cells , initiating the erythrocytic
schizogonic phase

12. b) Erythrocytic cycle :
- The merozoites released by pre-erythrocytic schizonts in the liver
invade the RBCs and grow to form the early trophozoite stage or
young trophozoites
- Early trophozoite consists of a ring of cytoplasm and a dot-like
nucleus
- The parasite feeds on the hemoglobin . it does not metabolize
hemoglobin completely and leaves behind hemozoin or malaria
pigment
-This early form develops to the mature trophozoite stage and then
undergoes multiple division into schizonts , producing a characteristic
number of a new generation of merozoites in each infected
erythrocyte.
-one of two fates await this new penetrant :
1. it may become another ring trophozoite and begin schizogony
anew
2. or it may become a male microgametocyte or a female
microgametocyte

13. Sporogonic cycle :
 When a female Anopheles mosquito ingests parasitized erythrocytes
along with its blood meal , the Asexual forms of malaria are digested
( gametocytes are unaffected by the digestive juices of the insect )
 The gametocytes undergo further development in the mid-gut
( stomach ) of mosquito
 Male gametocytes ( microgametocytes ) undergo a maturation
process known as exflagellation during which the nucleus undergoes
three mitotic divisions , producing 8 microgametes .
 a microgamete detaches from the mass and swims to the female
gametocyte ( macrogametocyte )
 macrogametocyte is fertilized by the microgamete to form zygote
 The zygote develops into a motile form called ookinete
 ookinete penetrates the epithelial linning of the mosquito stomach
wall and comes to lie beneath the basement membrane
 Ookinete develops into an oocyst within which numerous sporozoites
are formed

14.  The mature oocyst ruptures releasing sporozoites into the body
cavity and carried to the salivary glands of the insect
 The mosquito is now infective and when it feeds on humans , the
sporozoites are injected into skin capillaries to initiate infection
 The time taken for completion of sporogony in the mosquito is
about 1 – 4 weeks after the mosquito ingests the gametocytes ,
depending on the species and environment temperature

15. Life cycle variations : There are a number of differences in the
life cycle of the various types of Plasmodium that infect humans ,
some of which are important in clinical diagnosis

16. P. falciparum :
 Infect both young and old erythrocytes (i.e. erythrocytes of any age)
 10 % of the total erythrocyte population are infected
 Infected erythrocytes are not enlarged
 The trophozoite ( ring form ) :
 The early ring form is attached along the margin of RBC
(applique or accole form )
 Multiple rings may be seen within a single erythrocyte due to
multiple infections of single erythrocytes .
 Double chromatin are common in the ring form
 The schizont :
 the mature schizont produces 8 to 24 ( average 16 ) merozoites
 the erythrocytic schizogony takes about 36 – 48 h
 Rupture from infected erythrocytes is erratic , occurring at 48 hour
intervals with accompanying fever paroxysms
 The mature gametocytes : are crescent or banana shaped

17. Only ring trophozoites ( early trophozoites ) and gametocytes are
seen in the peripheral blood because the later stages of schizogony
( later trophozoites and schizonts ) are trapped in the internal
capillaries of muscle and visceral organs
A good stain will show coarse dots which are called Maurer’s clefts
( the pigment characteristic of P. falciparum-infected erythrocytes )
 Hemozoin, as well as Maurer’s dots or clefts , tend to aggregate
around the nuclear region of gametocytes

18. Plasmodium vivax and P. ovale :
 P. vivax and P. ovale selectively infect young ( immature )
erythrocytes ( reticulocytes )
 Less than 1 % of the total erythrocytes population is infected
 Infected erythrocytes are enlarged because these parasites prefer
to invade relatively larger reticulocytes ( this enlargement of
infected erythrocytes is less pronounced in P. ovale than in P.
vivax )
 Infected cells with P. ovale tend to be somewhat ovale in shape
with fimbriated margins .
The trophozoite :
The cytoplasm of the trophozoite stages is very irregular and
displays active amoeboid-like movement , hence the species name
( P. vivax from Latin meaning “vigorous” )
Trophozoite accumulates malarial pigment
The trophozoites of P. ovale resemble those in P. vivax , but are
usually more compact , with less amoeboid appearance

19. The schizont :
There are about 12 – 24 merozoites ( average 18 ) per schizont
The erythrocytic schizogony takes 48 h.
the schizont resemble those of P. malariae , except that the
pigment is darker
these rupture from the infected erythrocyte synchronously at 48
hour intervals , with accompanying fever
Gametocytes :
Both male and female gametocytes are large , filling almost the
enlarged RBC
In P. ovale , Both male and female gametocytes occupy nearly the
entire RBC
 good staining will show granules known as Schuffner’s dots in the
cytoplasm of the infected RBC
 all erythrocytic stages can be seen in peripheral smears

20. P. malariae :
 P. malariae prefers older erythrocytes
 It parasitizes about 0.2 % of the victim’s total erythrocyte
population
 no change in diameter of the infected erythrocyte , probably due
to the parasite’s affinity for older erythrocytes
The trophozoite :
early trophozoites accumulates hemozoin and the pink-staining
Ziemann’s dots ( can be seen with special stains )
The trophozoites stretch across the diameter of the erythrocyte
and is seen as a band form
morphologically , mature trophozoites resemble
macrogametocytes and are , therefore , difficult to distinguish

21. The schizont :
the mature schizont has an average of 8 merozoites , which
present as a rosette appearance .
erythrocytic schizogony takes 72 h. ( release of merozoites after
rupture of the infected cell synchronously every 72 hours with an
accompanying fever paroxsyms ( quartan malaria )
hemozoin usually accumulates as a dense mass in the center of
the schizont
 gametocytes :
Both male and female gametocytes occupy nearly the entire RBC

22. N. B. :
In all plasmodium-infected erythrocytes , two types of granules are
found :
1. One type ( schuffner’s dots in P. vivax and P. ovale ) :
is distributed throughout the cytoplasm of the erythrocyte
and usually stains pink to red when subjected to traditional
hematological stains , such as Giemsa’s Wright’s , or
Romanovsky’s
2. The second type is the coarse , dark hemozoin granules :
the by-products of hemoglobin degradation by the parasite .
 hemozoin is usually found more closely associated with the
parasite than with erythrocytic cytoplasm

23. Symptomatology :
 Vascular obstruction : occurs with P. falciparum because the
erythrocytes infected with schizont adhere to the endothelium of
capillaries in visceral organs .
 Black water fever : often accompany falciparum malaria infections
due to massive lysis of erythrocytes and production of high level of
hemoglobin in urine and blood .
Fever paroxysms : Periodic ruptures of infected erythrocytes are
accompanied by fever paroxysms that are usually synchronous except
during the primary attack .(the interval between paroxysms is species
specific . However , during the primary attack , infection may arise
from several populations of liver merozoites at different stages of
development .
 Malaria should be suspected from all cases of fever in people who
have returned from endemic areas within the previous 4 weeks .
It must be remembered that malaria can remain dormant :
P. malariae can persist up to 40 years
P. falciparum rarely persists more than a year but can be fatal .

24. Diagnosis :
1. Microscopic examination ( Gold standard )
 The most suitable way of diagnosing malaria is by finding parasites
in the stained peripheral blood film .
Demonstration of malarial parasite in the peripheral blood in thin
and thick smears
Thin smear is used for detecting the parasites and determining the
species by studying its morphological details (Species identification
is not easy in thick smear )
The thick smear is more sensitive and is used for detection of
malarial parasite when there is low parasitaemia
Both thin and thick smears can be used to determine the
parasitaemia level
2. Rapid diagnostic test ( RDT ) :
These tests aid in the diagnosis of malaria by detecting malaria
parasite antigens in human blood
3. Molecular diagnosis : PCR on blood

25. Preparation of thick films Preparation of thin films
Apply 4 drops of blood on a
microscope and spread
without excessive stirring to
form a smear approximately
1 cm2
Apply 1 drop of blood to the
slide
Field’s stain for thick blood
films
Giemsa stain for thin blood
films
Used for detecting the
parasites and determining the
species
Is more sensitive for detection
of malarial parasite in low
parasitaemia

26. Collection of blood samples :
Peripheral blood samples for diagnosis of malaria can be taken
from a finger prick or preferably into a tube with EDTA
anticoagulant .
The slides must be made immediately ; if the blood is left for
several hours in anticoagulant , the following effects may be seen :
 male gametocytes may develop and exflagellate , releasing
microgametes which may be mistaken for other organisms such as
Borrelia
Accole forms ( trophozoites seen at the edge of the blood cell ) ,
which are characteristic of P. falciparum , may be seen in P. vivax
infections because of re-invasion of the RBC by merozoites which
can’t enter the cell and are retained on the membrane
The morphology of the RBC may be altered by shrinkage
( crenation )

27. Blood samples should be :
If the slide is negative and malaria is still suspected , sample
should be repeated at 4-hourly intervals or just after or during
fever when the parasites are present at their highest density
during the apyrexial phase , the parasites disappear from the
peripheral blood and may not be seen at this time
Blood taken during the primary stage of infection ( i.e. during the
first 2 – 3 days ) , may not show parasites .
Repeat samples should also be taken during therapy to check the
parasitaemia of Plasmodium falciparum , particularly in cases of
initial high parasitaemia .
Taken prior to anti-malarial therapy

28. Determination of parasitaemia :
The number of parasitized RBCs ( parasitaemia ) in peripheral
blood is very important in :
In cases of Plasmodium falciparum :
 because they can be fatal illness
 if the parasitaemia exceeds 10 % , blood exchange may be
indicated
 An estimation of parasitaemia should be included when giving a
report on a case of Plasmodium falciparum .
 Parasitaemia of under 1 % need only be recorded as < 1 %
to evaluate the effectiveness of treatment

29. Method for estimation of parasitaemia :
Only areas of the thin film where the RBCs are 1 cell thick should be
examined
The number of RBCs in one of these fields should be counted and
an estimation made on 10 fields , using the same X100 oil
immersion lens and objective .
The number of parasitezed cells should be counted in 10 fields and
an average taken .
This figure ( number ) is divided by the average number of RBCs per
field and multiplied by 100 and the figure quoted as the % of
parasitized erythrocytes
% of parasitaemia =
𝒂𝒗𝒆𝒓𝒂𝒈𝒆 𝒏𝒐.𝒐𝒇 𝒑𝒂𝒓𝒂𝒔𝒊𝒕𝒊𝒛𝒆𝒅 𝑹𝑩𝑪𝒔 𝒑𝒆𝒓 𝒇𝒊𝒆𝒍𝒅
𝒂𝒗𝒆𝒓𝒂𝒈𝒆 𝒏𝒐.𝒐𝒇 𝑹𝑩𝑪𝒔 𝒑𝒆𝒓 𝒇𝒊𝒆𝒍𝒅
× 𝟏𝟎𝟎
The number of parasites in 1000 RBCS can be counted .

30. Prevention and control :
1. Chemoprophylaxis :
For travellers visiting endemic areas , chemoprophylaxis
provides effective protection
Prophylaxis should begin 1 week before travelling and be
continued while in the endemic area and for 4 – 6 weeks after
departure from endemic area
The drugs recommended are chloroquine , mefloquine or
proguanil
2. Vector control strategies :
(a) insecticide residual spraying ( IRS ) : the spraying of the indoor
surfaces of house with residual insecticides
(b) treated bed nets ( ITN )
(c) use of repellent , protective clothing , mosquito coils and
screening of house
(d) Elimination of mosquito breeding sites .