PLASMODIUM (Malaria Parasite)
Classification
Phylum - Protozoa
Sub Phylum - Plasmodroma
Class - Sporozoa - All members are parasite so
locomotive organs are absent
Order - Haemosporidia – Digenetic life cycle
Genus - Plasmodium
- Plasmodium is a member of order
Haemosporidia therefore it complets its life cycle in two hosts.
- Primary host - Primary host
for Plasmodium is human being. Plasmodium completes
only asexual life cycle in this host.
- Secondary host - Intermediate
host / Carrier host - Female Anopheles serves as secondary host
for Plasmodium. Both sexual cycle and sporogony asexual are
completed in this host.
- Reserviour host - Monkey is
reservior host for plasmodium
(Dog is also not affected).
- All the stages of Plasmodium life
cycle that occurs in human are also found in monkey, but monkey do not suffer
or die of malaria.
- Eradication of Plasmodium
is not easy due to its several hosts.
Another reason is that vaccine can not be formed because Plasmodium
do not induce human body to form antibodies and hence no immunity against Plasmodium
can develop.
- Number of chromosomes in Plasmodium
10
- NMEP - National Malaria Eradication
Programme
LIFE CYCLE OF PLASMODIUM IN HUMAN
There are two sites for activity of
Plasmodium in human
(i) Liver (ii) RBC
- All the activities that oocurs in
liver are known as "Exo erythrocytic Cycle".
- Whereas activities in RBC are termed
as "Erythrocytic Cycle".
INFECTION OF PLASMODIUM IN HUMAN
- Infective stage of Plasmodium
for human is sporozoite which are present around 2,00,000 in salivary
glands of female Anopheles.
- Sporozoites are spindle or sickle
shaped. Body is covered by pellicle which is made up of 11-15 microtubules.
- Sporozoite contains an aperture at
the apex called "Micropyle".
A structure which covers micropyle
is known as Apical cap. It is made up of 3 concentric microtubules.
A pair of secretory organells are
related to micropyle. It contains lytic enzymes which helps sporozoite to
penetrate human liver cells.
A big oral shaped nucleus is
present in middle of sporozoite. Just beneath it, there is a Mitochondria.
- This type of 2,00,000 sporozoites
are present in saliva of female Anopheles
- An anticoagulent is secreted when
female Anopheles bites. It do not allow blood to clot so that Anopheles,
can suck blood easily. With the saliva numerous of sporozoites enters in human
blood. Within 30 minutes all of these sporozoites approach the liver and no
sporozoite is visible in the blood.
Pre erythrocytic cycle
- The first cycle of Plasmodium
in liver is called as Pre erythrocytic cycle.
- Plasmodium starts its life
cycle from liver because
(i) To
prevent itself from the phagocytic action of WBC
(ii) Plasmodium use glycogen as food and liver is rich in glycogen
(iii) To multiply in number
- Sporozoite enters in the liver
cell and become spherical by phagocyting the cytoplasm. Now these are termed as
"Cryptozoites"
- Cryptozoites undergo multiple division.
This is called "Schizogony". This results in the formation of
1000-1500 small structure called as Cryptomerozoites. At this stage
cryptozoite is called "Schizont"
- Finally cell membrane of liver
cell & schizont bursts and Cryptomerozoites are now free in blood
sinusoids of liver.
- A few of these cryptomerozoites
infect RBC and start the erythrocytic cycle.
- Rest of the cryptomerozoites go
back in liver cells and starts the post exoerythrocytic cycle. All these
cycles in liver except the first one are called post exoerythrocytic cycles.
- Time taken to complete pre
erythrocytic cycle is called Pre
patent period. In this period Plasmodium is not visible in
blood.
Post Exoerythrocytic cycle
In this cycle Cryptomerozoites infect
the liver cells. They phagocyte the cytoplasm and become big and spherical. Now
these are known as Metacryptozoite or phanerozoites
Two types of Metacryptozoites are
formed
(i) Micro Metacryptozoites - (MICRO
MCZ)
(ii) Macro Metacryptozoites - (MAcro MCZ)
MICRO MCZ are further
converted into 100-1000 merozoites by the process of schizogony. The product is
called Micro meta crypto merozoite (Micro MCM).
Macro MCZ also undergo the process of schizogony. It
results in the formation of 64 merozoites these are called Macro meta crypto
mero zoite (Macro MCM).
- Micro MCM infect only RBC whereas
Macro MCM infect liver cells
- This cycle goes on repeating
again and again which causes destruction of liver cells. In case of an
excessive Malaria, liver may damage and jaundice like symptoms may appear.
Erythrocytic
cycle or Golgi cycle
- This cycle starts at first by cryptomerozoites
and further carry on by Micro meta cryptomerozoite.
- Cryptomerozoite infects
R.B.C. They phagocyte Haemoglobin of R.B.C & become big &
spherical. Then they are called Trophozoites. Later on a big central
vacuole is formed in the cytoplasm of trophozoite. This makes it appear like a
"Ring". So this stage is called Signet ring stage. After a
while vacuole is lost and trophozoite become irregular in shape. At this stage
Plasmodium looks like Amoeba so this is called as Amoeboid stage. This
is active and feeding stage of Plasmodium. It phagocytes Haemoglobin
quickly and grows up and occupies whole of the RBC approximately.
Particularly, at this stage reddish brown coloured
granules are seen in the cytoplasm. These are called Haemozoin granules.
It is the non digested haeme part of haemoglobin.
At
the same time bright yellow coloured granules appear in the cytoplasm of RBC.
These are called Schuffner's dots which are probablely waste product of Plasmodium. These dots
are used in diagnosis of malaria because they are the most clear structures
that appear in blood. A stain known as Romanovaski stain is used to
observe schuffner's dots.
There are two species of Palsmodium
that do not form schuffner's dots.
1. Plasmodium malariae -
They form Red coloured granules known as Zeiman's dots
2. Plasmodium falciparum
- They form green coloured Maurer's dots/Clefts.
Both of these are also helpful in
diagnosis of malaria
Now schizogony occurs in
trophozoite and 12-24 Merozoites are formed. They are arranged as petals
of flower. So Plasmodium looks like a flower and hence this stage is
known as Rosette stage.
Some cytoplasm in this stage
remains undivisible. Haemozoin granules are present in this cytoplasm.
Finally membrane of RBC and
schizont bursts and all the material get freed in blood plasma. Merozoites infect
new RBC and repeats the erythrocytic cycle again and again. Organells like
apical cap, secretory organells etc. get fused to form Rhoptries stage in
merozoites.
Burst RBC is called Ghost RBC.
Spleen uptake these ghost RBC from the blood and destroy it. A special type of
phagocyting cells called as Macrophages are present in spleen, These
cells secrete an enzyme Lysolecithin which destroy ghost RBC.
In case of excessive malarial
infected spleen becomes large and swollen. This disease is called Megaly of
spleen or spleen index. It is due to increase in number of macrophages and
lysolecithin causes swelling.
Excessive malaria infection may
also lead to anaemia because more lysolecithin secretion occurs which reaches
to blood and destructs the healthy RBC's so decrease in number of healthy RBC
cause Anaemia. This anaemia is called Haemolytic anaemia.
The time lapse between infection of
Plasmodium and first attack of Malaria is called Incubation period.
- Plasmodium shows
biological clock system because erythrocytic cycle is completed exactly with in
48-72 hours.
EFFECT OF HAEMOZOIN GRANULES
Due to toxic effects on body,
symptoms of Malaria appear.
Initial symptoms of Malaria -
Nausea, Constipation, Bodypain, Dyspnoea, weakness in body.
- After 2 or 3 Erythroytic cycles
haemozoin granules increase in number and actual symptoms of Malaria now begins
to appear. This is called Paroxysm of malaria. It has three stages.
1. Rigor stage :- Alternate contraction and relaxation in
muscles causes shivering and cold sensations.
2. Febrile stage :- After some time shivering stops and
body temp rises due to contraction of muscles. Rise in temprature is benificial
for patient because internal high temp is unfavourabale for parasite Plasmodium.
3. Difervescent stage :- After rise in temprature excessive
sweatning occurs and body temprature decreases. Now patient feels himself
healthy. But at this time erythrocytic cycle starts again and fever is repeated
at a constant interval of time.
POST ERYTHROCYTIC CYCLE
Sometimes Merozoites formed by
erythrocytic cycle escapes from blood and enters the liver cells. These
merozoites remain inactive in liver.
After a long time they become
active and multiply in number. This causes Malaria again. So after a long time
malaria is repeated again this is called Relapse of Malaria.
Post erythrocytic cycle is not
found in Plasmodium falciparum. So relapse of malaria do not
occur. Longest relapse of Malaria found in Plasmodium malarie may
last up to 3 years.
GAMETOCYTE STAGE
When many Erythrocytic cycles
completed then merozoites enter the RBC and form a new stage called as Gametocyte
or Gamonts or Resistant Trophozoite schizont. Merozoite stage
contain Rhoptries.
Gametocyte is the last stage in
human. Further development occurs in female Anopheles because high temperature
in human is unfavourable for gametocyte formation. There is biological clock
system in Plasmodium it means that it form gametes when there is more
probability of attack of female anopheles. So gametes are formed in night, from
late evening up to midnight. Gametocytes which reach in female Anopheles are
developed and rest which are left in blood are destryoed in the morning.
Two type of gametocytes are formed
(1) Micro gametocyte
(2) Macro gametocyte
These are formed in ratio of 1 : 2
respectively.
LIFE CYCLE OF PLASMODIUM IN FEMALE ANOPHELES
There are two type of cycles :
(1) Gametogony - Sexual
cycle (2) Sporogony -
Asexual cycle
Gametocyte is the infective stage
of Plasmodium for female Anopheles. When it sucks blood, many
stages reach in its Crop but only gametocyte stage remains, rest of all are
digested.
I Gametogenesis
- Microgametocytes
undergo the process of Spermatogenesis in which its nucleus is divided
into four haploid nuclei by meiotic division. Further, Mitosis occurs and these
are converted into 8 nuclei. All nuclei are arranged on periphery. At the site
of every nucleus plasmalemma projects outward and eight spindle shaped
projections are formed. Every projection contains a nucleus and few cytoplasm.
These projections are called Sperms. Sperm formation process is exflagellation.
Every sperm detaches itself from microgametocyte by constricting at its base.
So eight sperms are formed by a single microgametocyte.
Macrogametocytes form ovum
by the process of Oogenesis in which meiosis occurs and one ovum and
three polar bodies are formed. Polar bodies are destroyed further. A projection
appears on ovum which is called reception cone. This is the penetration
site of sperm at the time of fertilization. Zygote is formed as a result of
fertilization. Whole of this process up to zygote formation occurs in lumen of
crop. Zygote can form in any type of mosquito e.g. Anopheles, Culex and Ades
etc but further development of zygote is possible only in female Anopheles.
This is the host specialisation of Plasmodium.
DEVELOPMENT OF ZYGOTE
Proposed
by "Grassi". This theory says that all zygotes are converted into
long worm like structures called Ookinete or vermicule. With the help of
gliding and wringling movements These ookinete enters the crop wall and are
place beneath the outermost layer called peritoneum of crop wall.
A thin and elastic coat is secreted
around these zygotes by both zygote and cells of crop wall. This stage is
called Oocyst. At this stage 50-100 small projections of oocyst are
found on the crop wall.
II. SPOROGONY- Oocyst
takes nutrition from crop wall and develop into 5-6 times bigger structure
called sporont. Many small vacuoles are now formed in the cytoplasm of
sporont. Nucleus of sporont is converted by free nuclear divisions into
approximately 10,000 nuclei. All these nuclei are arranged on periphery of
vacuoles. Later on cytoplasm is divided and converted into 10,000 parts around
every nucleus, with the result 10,000 sporozoites are formed. This sporont is
called as sporocyst.
Outermost layer of crop and wall of
sporont bursts and these sprozoites are now free in haemocoel of mosquito.
Haemocoel is a blood filled cavity. This blood is colourless and called
haemolymph.
All sporozoites are stored in salivary glands. About
2,00,000 sporozoites are stored in salivary glands of mosquito which furhter
infect to human through saliva.
SPECIES OF
PLASMODIUM :- About 60 species are known but only four are
pathogenic
(1) Plasmodium vivax
(2) Plasmodium ovale
(Not found in India, Found in Phillipens & Africa)
(3) Plasmodium falciparum
(4) Plasmodium malariae
Most common is - Plasmodium
vivax and very rare is - Plasmodium ovale
Comparative Study
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S.N. Particulars
|
P. vivax
|
P. ovale
|
P.
falciparum
|
P.
malariae
|
|
1.
|
- Prepatent
period
|
8-10 days
|
9 -days
|
5-6 days
|
14-15 days
|
2.
|
- Time period
|
48 hours
|
48 hours
|
36-48 hours
|
72 hrs.
|
of Erythroytic
cycle.
|
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3.
|
- Incubation
period
|
12-14 days
|
12-14 days
|
12 days
|
27-37 days
|
4.
|
- Life cycle in
|
10-17 days
|
16 days
|
22-23 days
|
30-35 days
|
mosquito
|
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5.
|
- Type of
malaria
|
Benign tertian
|
Mild tertian
|
Lethal malaria
|
Tetrac fever
|
fever
|
fever
|
Subtertian
fever,
|
quartan fever
|
||
Tropical fever,
|
sub clinical
fever
|
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Cerebral fever,
|
Least harmful
|
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Blackwater
fever,
|
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Malignant or
|
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Aestivo-autumnal
|
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- Malaria caused by Plasmodium
falciparum is called lethal malaria. It is also termed as sub tertian
fever, tropical fever, cerebral fever, black water fever, Malignant fever or
Aestivo-autumnale fever. This is the most dangerous malaria because infected
RBC adhere and form thrombus which may interfere the blood circulation.
Carotid artery is feeding artery of
brain so when, this artery is blocked by thrombus then brain may suffer from
less blood circulation which is unfavourable for it. Longer duration of this
condition may cause death.
When thrombus is formed in coronary
arteries, which gives nutrition to heart, heart attack may occur. Loss of
Haemoglobin through urine(Haematuria) occur in which colour of urine changes
from yellow to black hence it is also called as 'Black water fever'.
Double signett ring and crescent
gametocyte are characteristic of Plasmodium falciparum.
- Malaria by Palsmodium
malarie is difficult to diagnose because this species may remain
dormant in liver for a very longer period.
HISTORY OF MALARIA
1. Mc. Culloh - Named
Malaria
2. Lancisi - Suspect that
there is any relation in between mud mosquito and malaria.
3. Charles laveran -
discovered Plasmodium
He observed Plasmodium first
in RBC of human and revealed that malaria is caused by Palsmodium.
4. Sir Ronald Ross - Proved
the relation between mosquito and Malaria. He saw oocyst first on crop of
female Anopheles. About 25,000 mosquitoes were dissected by Sir Ronald Ross in
his life.
Female Anapheles is the carrier of Plasmodium.
The discovery of sir Ronald Ross was awarded by Noble Prize on 29th of
August 1902. Hence this day is celebrated as "Malaria day"
It was an incident that Sir Ronald
Ross died of Malaria.
5. Grassi - Studied the life
cycle of Plasmodium in female Anopheles.
6. Mc. Collum - Explained in
detail the sexual cycle of Plasmodium.
7. Shortt, James, Huff &
tate - studied the life cycle of Plasmodium in human.
8. Golgi & celli -
explained erythrocytic cycle so this is also called golgi cycle.
9. Schauddin - Detailed
study of Plasmodium vivax life cycle in human and mosquito.
10. Rudzinska - Study
of ultra structure of Plasmodium by electron microscope.
CONTROL OF MALARIA
(1) Direct - by killing Plasmodium
(2) Indirect - by killing
mosquitoes
(1) Indirect - following procedures are used to kill mosquitoes.
(a) Insecticides like - DDT (It is now banned) Gamaxene, Melathion
etc. are sprayed.
(b) Biological
control - This is the more suitable procedure. In this larvivorous fishes are
used. They eat larva of mosquitoes. e.g. Gambussia Trout, minnows, stickle
back.
(2) Direct method - Plasmodium is destroyed by chemotherapy
(a) Old
medicines like Quinine - it is obtained from Cinkona as quinine sulphate salt.
It destroys only those stages of plasmodium which are present in blood.
(b) Mapacrine - It destroys merozoites present in blood
(c) Paludrine and sulphadoxine - These medicines destroy all the stages
either in blood or in liver. But are not generally used because they cause harm
to liver cells.
(d) The most effective medicine for Malaria is Deraprim. It
destroyes gametocytes.
SPECIAL POINTS
(1) 29th August is Malaria day
(2) Plasmodium is a member of sporozoa class
(3) Monkey acts as Reservoir host of Plasmodium
(4) Lysolecithin secreted by spleen destroyes infected RBC's
(5) Normally primary host is the host in which parasite completes
its sexual life cycle but in Plasmodium human is primary host
exceptionally. Although sexual cycle is completed in mosquito and asexual in
human.
(6) Maximum amount of Haemozoin granules is present in gametocyte
stage.
(7) Temprature of Malaria patient may rise up to 104-1050 F.
(8) Some other symptoms and side effects may appear from malaria
like Anaemia, Jaundice, Megaly, Thrombosis, Insomnia.
(9) The most effective medicine for Malaria is Deraprim. It
destroyes gametocytes.
(10) Number of lymphocytes is increased in malaria infection.
(11) Shivering characteristic of malaria is caused by merozoites are
liberated with toxin from RBC.
(12) Number of chromosome in Plasmodium - 10
(13) Merozoite
stage of Plasmodium contain Rhoptries.
Problem for practice
1. Malaria is caused by
(1) Mosquito
(2) Foul air
(3) Ascaris
(4) Plasmodium
2. Gametocytes of malarial parasite are formed in
(1) Blood of man
(2) salivary glands of Anopheles
(3) Stomach of female Anopheles
(4) stomach of male Anopheles
3. In Malarial parasite schizont stage occurs in
(1) RBC of man
(2) Blood of Anopheles
(3) Stomach of Anopheles
(4) Salivary glands of Anopheles
4. Contractile vacuole is likely to be absent in
(1) Euglena
(2) Plasmodium
(3) Amoeba
(4) Paramoecium
5. Sporogony in the life of Plasmodium occurs in
(1) RBC of man
(2) Liver of man
(3) Salivary glands of mosquito
(4) Stomach wall of mosquito
6. Quinine is extracted from
(1) Leaves of Occimum
(2) Bark of Cinchona
(3) Bark of Cinnamon
(4) Stem of Hevea
7. Exoerythrocytic phase of life cycle in malarial parasite occurs in
(1) Liver of man
(2) Reticulo-endothelium of man
(3) Brain of man
(4) stomach of mosquito
8. Sexual phase of life cycle in Plasmodium occurs in
(1) Blood of man
(2) Gut of mosquito
(3) Salivary glands of mosquito
(4) Body cavity of mosquito
9. Trypanosomiasis is disease transmitted by
(1) Tse tsefly
(2) Fire fly
(3) May fly
(4) Louse
10. Malarial parasite can be best obtained from the patient
(1) Five hours after temperature becomes normal
(2) When temperature rises with vigour
(3) One hour before rise of temperature
(4) Any time
11. During schizogony in malarial parasite the resulting cells are called
(1) Merozoites
(2) Ookinetes
(3) Sporozoites
(4) schizonts
12. Which is the infactive stage of Plasmodium in man
(1) Sporozoite
(2) Ookinete
(3) Merozoite
(4) Schizont
13. At which stage Plasmodium infects the liver of man
(1) Sporogony
(2) Erythrocytic cycle
(3) Pre-erythrocytic cycle
(4) Gamogony
14. Relationship between mosquito and malaria was proved by
(1) Rosenhof
(2) Pasteur
(3) Ronald Ross
(4) Lancisi
15. Sleeping sickness in man is caused by
(1) Trypanosoma
(2) Entamoeba
(3) Plasmodium
(4) Leishmania
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