Plasmodium, Chapter Notes, Class 11, Biology PDF Download

PLASMODIUM

GENERAL CHARACTERISTICS

Classification

Phylum     -      Protozoa
                        Unicellular or Acellular
                        organism

Class      -        Sporozoa
                        Sporozoites are elongated
                        worm like ; sexual
                        reproduction occurs.
                        Life cycle digenetic,
                        intracellular parasites of
                         RBCs, schizogony in
                         primary host, motile zygote.

Genus     -         Plasmodium
                          Parasite of RBC of mammals,
                          reptiles and birds, vector host
                          usually mosquito.

Introduction

(i) Plasmodium name was given by Marchiafava and celli.
(ii) Plasmodium was discovered by Laveron.

Species

(i) In humans only 4 species causes disease. These 4 species are as follows :
Plasmodium vivax.
Plasmodium falciparum.
Plasmodium malariae.
Plasmodium ovale.
(ii) P. vivax is the most common species which is found in India.
(iii) P. ovale is found in Phillippines and tropical Africa.
(iv) In birds 2 species of Plasmodium are found, these 2, species are as follows :
Plasmodium gallinaceum.
Plasmodium praecox.
Note :Amoeboid phase remains absent in species of Plasmodium found in birds

2. LIFE CYCLE

(i) Life cycle of Plasmodium is digenetic.
(ii) Man is the primary host.
(iii) Female Anopheles is the secondary host.
(iv) Female Anopheles can be also called intermediate vector.
(v) In India four species of Anopheles is found which spread Plasmodium.

These 4 species are as follows :
(a) Anopheles maculatus.
(b) Anopheles stephensi.
(c) Anopheles culicifacies.
(d) Anopheles fluriatiles.

Note :
(i) Monkey is the reservoir host.
(ii) In Reptiles and Aves secondary host is culicine mosquito.

Trophozoite

(i) A fully grown malarial parasite is called trophozoites.
(ii) Trophozoites lives inside R.B.C. of man.
(iii) Trophozoite remain surrounded by double membranous cell membrane.
(iv) Within the cell, endosplasmic reticulum, free ribosome, mitochondria and golgi complex is found.
(v) No contractile vacuole is found within the cell.

Note :No. of chromosome in Plasmodium are 14.

Life cycle of Plasmodium in man

(i) In human body Plasmodium complete its life cycle at two places, these places are liver and RBC.
(ii) In liver Pre erythrocytic cycle and Exo-erythrocytic cycle is found.
(iii) In RBC Erythrocytic cycle is found.

Infection to the healthy man

(i) Sporozoite is infective stage of Plasmodium in human body.
(ii) When female Anopheles bites human, she injects sporozoite in the body.

Note :In male Anopheles only sucking type mouth part is found.
(iii) Sporozoites are found in salivary gland of female Anopheles.
(iv) Number of sporozoites in its salivary gland is approximately 2 Lakhs.
(v) In saliva of female Anopheles anticoagulant is found which prevents coagulation of blood.
(vi) When saliva enters in the human body it causes itching and burning.

Structure of the sporozoite

(i) Structure of sporozoite was studied by Graham.
(ii) Sporozoites are spindle or sickle shaped.
(iii) In sporozoite only one elongated nucleus is found.
(iv) Length of sporozoite varies from 6  to 15 .
(v) Body of sporozoite remain covered by pellicle.
(vi) Within pellicle of sporozoite microtubules are found which helps in wriggling movement of sporozoite.
(vii) Number of microtubules varies from species to species.
(viii) At anterior end of sporozoite 3 or 4 concentric rings are found which combindly form a structure called apical cap.
(ix) At the tip of the sporozoite a small aperture is found called micropyle.
(x) Two secretory organelles remain attached with micropyle.

Function of Secretory organelle
Secretory organelle secretes lytic secretion which helps in penetration of sporozoite within the liver.
(xi) At posterior end of sporozoite, 1 mitochondria is found.
(xii) Within 1/2 an hour all sporozoites disappear from blood stream and attacks the liver.

Pre-erythrocytic phase or Pre erythrocytic schizogony

(i) Within liver cell sporozoite actively feed on its cytoplasm.
(ii) Because of feeding sporozoite becomes some what spherical structure approximately 45  in size, called schizont.
i.e. sequence of pre erythrocytic phase is Sporozoite  Cryptozoite  Schizont  Cryptomerozoites.
(iii) In schizont multiple fission takes place as a result 1000-1500 cryptozoites are formed and such multiple
fission is called schizogony.

Note : Cryptozoites are also called merozoites or cryptomerozoites.

Microtubules
a. Plasmodium vivax 11
b. Plasmodium ovale 13
c. Plasmodium falciparum 15
d Plasmodium malariae Not known

(iv) Due to excessive pressure of cryptomerozoites, schizont and liver cell get ruptured and cryptomerozoites get released in sinusoids (blood sinuses) of the liver.
(v) Cryptomerozoite attacks new liver cells and starts pre exo-erythrocytic phase.
(vi) Some of the cryptomerozoites attacks erythrocytes and starts erythrocytic cycle.
(vii) Time taken to complete pre erythrocytic cycle is called ‘Pre-patent period’. In this period ‘Plasmodium’ is not visible in blood.

Exo-erythrocytic phase or Exo-erythrocytic schizogony

(i) Like sporozoites cryptomerozoites attacks on liver cells and feeds on its cytoplasm and get enlarged in shape and become schizont.
(ii) Like pre-erythrocytic phase, multiple fission (schizogony) takes place in the nucleus of schizont, as a result numerous metacryptomerozoites get formed.

Note : Metacryptomerozoites is also called phanerozoites.

(iii) Metacryptomerozoites are of 2 types-
(a) Micrometacryptomerozoites
(b) Macrometacryptomerozoites

(a) Micrometacryptomerzoites
(i) It is small is size.
(ii) It attacks on erythrocytes and continues erythrocytic cycle.

(b) Macrometacryptomerozoites
(i) It is large in size.
(ii) It again attacks on liver cell and continues exo-erythrocytic cycle.

Note :
(i) Because of repeated attack of macrometacryptomerozoites liver get damaged.
(ii) In P. falciparum no exo-erythrocytic phase is found.

Erythrocytic cycle

(i) This cycle was studied by golgi hence it is called golgi phase.
(ii) Erythrocytic phase get completed in 48 hours.
(iii) When micrometacryptomerozoites attacks RBC, erythrocytic phase starts.
(iv) Generally one micrometacryptomerozoites attacks one erythrocytes only.
(v) In erythrocytic phase following stages are found-

(A) Trophozoite stage
Micrometacryptomerozoites within erythrocytes feeds on cytoplasm get developed into trophozoite stage,
which is adult stage of the Plasmodium.

(B) Signet ring stage
Trophozoite increase in size and a non contractile vacuole get formed in the trophozoite.
Nucleus get arranged at one corner as a result ring like structure get formed, this stage is called signet
ring stage.
Note : Signet ring stage remains absent in Plasmodium falciparum.

(C) Amoeboid stage
(i) This stage is also called growth period.
(ii) In this stage vacuole disappears from the trophozoites.
(iii) Trophozoites starts feeding more actively upon cytoplasm and haemoglobin of the host RBC.
(iv) It absorbs the cytoplasm of the RBC by diffusion through its surface or by active pinocytosis.
(v) Haemoglobin breaks down into globin and the red pigment hematin. Globin get digested.
(vi) Haemozoin a poisonous substance get formed from hematin.
(vii) A number of yellow and orange coloured granules get formed in cytoplasm of RBC which is called schuffner’s granules.

Note : It is believed that schuffner’s granules get formed from excretory substances of the parasite.

(viii) Schuffner’s granules varies from species to species of the Plasmodium.
In P. vivax schuffner’s granules are yellow and orange coloured.
In P. ovale schuffner’s granules are like vivax called James dot.
In P. falciparum schuffner’s granules are brassy coloured called Maurer’s dot.
In P. malariae schuffner’s granules are Zeimann dots.
Note : Schuffners granules appears most clearly in blood during blood test for malaria. Schuffners dots are waste product of Plasmodium. ‘Romanovaski stain’ is used to observe schuffner’s dots.

(D) Schizogony of erythrocytic cycle

(i) Amoeboid phage increases in size and becomes round, now it is called schizont.
(ii) Nucleus of schizont undergoes multiple fission as a result 12-24 daughter nucleus get formed.
(iii) Daughter nucleus goes to periphery and cytoplasm accumulates around it and schizoids get formed.
(iv) Schizoids remain arranged on the periphery of schizont and haemozoin in the middle, this stage is called Rosette stage.
(v) Finally both schizont and RBC get burst.
(vi) Schizoites and haemozoin both get liberated in the blood.
(vii) Liberation of haemozoin leads to shivering and malarial fever.
(viii) In P. vivax upto this stage, cycle get complete in 48 hours.So after every 48 hours malarial fever get repeated.
(ix) The ruptured RBC called ghost are destroyed in the spleen so, spleen is called graveyard of RBC.
(x) The interval between inoculation of sporozoites in human blood and first attack of the fever is called Incubation period.
(xi) Within spleen ruptured RBC is dissolved by lysolecithin, secreted within spleen.
(xii) Free merozoites again attacks to RBC, which cause anemia in the host.
(xiii) In this disease, liver and spleen also get increased in size hence called hepatomegaly and spleen

Spleenomegaly.

Note : Size of spleen increases due to two reasons–
(i) Due to rise in number of phagocytic cells.
(ii) Due to excessive secretion of lysolecithin.

(E) Development of Gametocyte

(i) After number of erythrocytic cycles some merozoites invading RBC donot grow into normal schizonts but into a different kind of rounded form called gametocytes.
(ii) Gametocytes get matured in bone marrow and spleen in about 96 hours.
(iii) Ratio of microgametocyte and macrogametocyte is 1 : 2. Gametocytes are of two types :

(I) Microgametocyte
(II) Macrogametocyte
(I) Microgametocyte
(a) Microgametocyte is male gametocytes
(b) Male gametocyte are less in number

SEXUAL CYCLE IN MOSQUITO

(c) In male gametocyte haemozoin remain scattered in cytoplasm
(d) Microgametocyte is small in size
(e) Large nucleus is found in microgametocyte.
(f) No reserve food is found in microgametocytes
(g) Cytoplasm of male gametocyte is slightly brown in colour.

(II) Macrogametocyte

(a) Macrogametocyte is female gametocytes.
(b) Macrogametocyte is large in shape.
(c) Macrogametocyte are more in number.
(d) Reserve food is found.
(iv) Further development of gametocytes are not possible in human body, because of high body temperature.
(v) Gametocytes remain alive in the body for 1-2 day only.
(vi) Gametocytes is infective stage for mosquito.

Microgametocyte Macrogametocyte

1 Nucleus Big and Central Small & eccentric
2 Store food Less quantity More quantity
3 Haemozoin Less & diffused granules More
Life cycle of Plasmodium in mosquito (Infection to mosquito)

In gametocytes maximum Haemozoin is found.

(i) When female Anopheles sucks blood of infected person. Anopheles sucks gametocytes along with blood. Blood get digested in the crop.
(ii) In culex even gametocytes get digested.
(iii) Because low temperature in the mosquito gametophytes becomes functional.
(iv) Crypto merozoite only remain functional at high temperature hence cryptomerozoite which comes in mosquito crop do not survive.
(v) In female Anopheles life cycle of Plasmodium includes following stages :

Gamogony or Gametogenesis

(i) During gametogenesis gametocyte which comes in the mosquito stomach form sex cells or gametes.
(ii) Gametogenesis includes :

(A) Male gamete formation
(B) Female gamete formation

(A) Male gamete formation

(i) Nucleus of microgametes undergoes meiosis, it result in formation of 4 haploid nuclei.
(ii) Each haploid nuclei undergoes mitosis as a result 8 haploid nuclei get formed.
(iii) Each haploid nuclei moves towards periphery of microgametocyte cytoplasm accumulates around nuclei.
(iv) Each cytoplasmic mass along with nucleus shoots off from the surface of microgametocyte in the form flagella, each flagella form microgametes or sperm this process is called exflagellation.
(v) Microgametes detach from parent gametocyte.
(vi) 1 microgametocytes 8 microgametes or sperm get formed.

(B) Female gametes formation

(i) Nucleus of macrogametocyte undergoes meiosis as a result 4 haploid nuclei get formed.
(ii) 3 nuclei develop into polar body.
(iii) Only one ovum get formed from one gametocyte.
(iv) On the surface of ovum conical bulb appears, which is called reception cone or cone of fertilization.

Fertilization

(i) Sperm fuses with cone of fertilization.
(ii) Cytoplasm of the sperm mixes with cytoplasm of the ovum and the nuclei of the two fuse to form diploid zygote syncaryon.
(iii) Zygote get formed in the stomach of mosquito after 9 to 10 days of infection.
(iv) Sygamy is anisogamous type.
Ookinete
(i) Zygote is some what spherical in shape after some time becomes long worm like called ookinete or
vermicular.
(ii) Anterior end of ookinete remain pointed while posterior end remain thick.
(iii) Ookinete is 15 to 30  long and 3  thick.
(iv) Its thick end is dark in colour because haemozoin granules are found on thick end, pointed end remain
colourless.

Penetration and Encystment

(i) By help of lytic secretion lighter end of ookinetes penetrates wall of stomach.
(ii) On reaching beneath the peritoneal covering of stomach wall, ookinete becomes immobile, reassumes spherical shape and soon becomes enclosed within a cyst about 8 to 10  in diameter.
(iii) The cyst wall is thin, semipermeable and elastic.
(iv) It is partly formed by secretion of zygote and partly by tissue of stomach wall.

Oocyst

(i) Its encysted zygote is called oocyst.
(ii) Just 1 to 2 days after fertilization 50 to 500 nodules appears on the stomach of infected female
Anopheles.
Sporulation

(i) By actively getting nourishment from stomach wall oocyst grows 5 to 6 times in size.
(ii) Nucleus of oocyst undergoes to mitotic division, because of this within 2-3 days 10,000 daughter
nucleus get formed.
(iii) Cytoplasm accumulates around each daughter nucleus, each cytoplasmic mass becomes elongated
and spindle shaped called sporozoites.
(iv) Due to pressure of sporozoites oocyst break, and sporozoites get liberated into the haemocoel of the host.
(v) Finally sporozoites get accumulated in salivary gland.
(vi) Nearly 2 lakhs sporozoites are found in infected Anopheles.

Note :Sporozoites are diploid

3. MALARIA

History of malaria

(i) Name malaria was given by Maculoch.
(ii) Lancisi at first suspected close relationship among malaria, mosquito and mud.
(iii) Charles laveran at first discovered Plasmodium in RBC of human being.
(iv) He discovered amoeboid form.
(v) He at first described ‘Plasmodium is a malarian parasite, and malaria occurs because of infection of Plasmodium’.
(vi) Golgi confirmed Laveran’s discovery by observing stages of P.malariae in human RBC.
(vii) Sir Ronald Ross at first described that he at first observed oocysts of Plasmodium in female Anopheles.
(viii)Sir Ronald at first described that malaria is transmitted by Anopheles.
(ix) For his work he won Nobel prize in 29th August 1902.
(x) Malaria day is celebrated on 29th August.

Note : First Malaria day was celebrated in 1902.

(xi) Grassi (1900) fully described the life cycle of Plasmodium in the stomach of Anopheles host.
(xii) Mc. Cullum at first Studied sexual cycle of Plasmodium in detail.
(xiii) Short and Garnham (1948), Shortt (1949), Jeffrey (1952) Bray (1960) have demonstrated preerythrocytic and exoerythrocytic stages of various Plasmodium species of man.
(ix) Golgi and Celli, studied erythrocytic cycle of schizogony.

Effect of malaria on human body

Following are the effect of malaria on human body.

(i) Anaemia (Reduction in haemoglobin)
(ii) Jaundice (Concentration of bilirubin increases)
(iii) Thrombosis (Blood clotting)
Note : Thrombosis is seen in Plasmodium falciparum.
(iv) Insomnia (Loss of sleep)
(v) Spleenomegaly (Inflammation and enlargement of spleen)
(vi) Hepatomegaly (Inflammation and enlargement of Liver)

Symptoms of malaria
Prodromal symptoms

(i) Prodromal symptoms, includes mild symptoms which appears early.
(ii) These mild symptoms are as follows :
(a) Loss of appetite
(b) Constipation.
(c) Muscular and joint pain
(d) Nausea
(e) Mild chill

Paroxysm of malaria

(i) It is actual clinical attack of malaria which initially begins after a few earliest erythrocytic cycle.
(ii) Paroxysm results due to sufficient accumulation of haemozoin and other toxin in the blood.
(iii) Duration of paroxysm varies from person to person and include 3 stages
(a) Rigor stage (b) Fibrile stage
(c) Defervesent stage
(a) Rigor stage

In this stage person feels chill and shivering, rapid pulse and severe headache.

(b) Febrile stage
In this stage body temperature rises up-to 104º to 105º F.

(c) Defervescent stage
In this stage following changes takes place
(i) Sweating start profusely.
(ii) Temperature of the body comes down.
(iii) Patient feel sexhaust and weak.

Duration between infection and appearance of symptoms of malaria is called incubation period.
Prepatent period
Duration in between infection and entrance of parasite within erythrocyte is called prepatent period.
Recurrence period
(i) Duration in between two malaria attack is called recurrence period.
(ii) Varies from species to species.

Duration of period in malaria

Types of malaria

Malaria are of numerous type.
Beningn or tertian malaria
(i) Caused by P. vivax and P. ovale.
(ii) Death rate is almost negligible in this type of malaria.
(iii) This type of malaria causes brain fever.

Malignant malaria
Caused by P. falciparum pernicious cerebral malaria.
(i) Also called Estivo autumnal malaria or pernicious malaria or cerebral malaria.
(ii) Maximum death rate is seen with this type of malaria.
(iii) In this type of malaria blood clot occurs in blood capillaries.
(iv) Death occurs because of obstruction of blood capillaries and delicate organs of the body.
(v) In this type of malaria destruction of RBC takes place.
(vi) Haemoglobin get excreted in urine called black water fever.

(i) Some merozoites become dormant in the liver cell and remain inactive for long duration even up to years.
(ii) After long duration merozoites become functional and causes malaria, this condition is called Relapse of malaria. Post-erythrocytic phase basically relates to the ‘Relapse of malaria’Parasite temporarily‘ becomes inactive in liver cells.

Note : Plasmodium malariae may remain in inactive state for 3 long years so longest duration of relapse of malaria is seen in Plasmodium falciparum.

Control and eradication of malaria

(i) To control and eradicate malaria (NMEP) National Malaria Eradication Programme is being runned in India.
(ii) Indian government have started, NMEP in 1953.

Following are the important steps which are helpful in controlling and eradication of malaria.

By Destruction of mosquito (Adult and Larva)
(i) Adult mosquito are killed by spraying DDT and pyrethrum. Neptha, Tetracamphor, Cresol are burnt to kill adult mosquito.
(ii) Stagnant water is the breeding place of adult mosquito so, stagnant water is drained, as a result Larva pupa, do not survive.
(iii) Spraying of kerosene oil in stagnant water is one of the best way of destruction of larva and pupa of the mosquito.

Reason
Kerosene oil forms a film or layer on the surface of water, as a result pupa fails in breathing and dies due to suffocation.
(iv) BHC or Gamahexene and parisgreen are larvicidal and are being frequently used.
(v) Biological methods are used in destruction of pupa and larva. e.g. Gambusia, Trouts, Minnows all are (insectivorous) fishes.

Note :Biological methods means destruction of pupa and larva by using living animals and plants.

By adopting prophylaxis methods

(i) Nets, mosquito repellant creams are used as a preventive measure against mosquito.
(ii) Some drugs like quinine and Deraprim are regularly used to get prevented from mosquito.

Note :
(i) Quinine is obtained from the bark of cinchona tree.
(ii) Cinchona tree grows in, dutch, East indies, India, Peru, Ceylon etc.
(iii) Quinine kills merozoite.
By using drugs (Chemotherapy)

Numerous drugs are used in treatment of malaria prominent drugs are as follows:

(i) Quinine
(ii) Mepacrine
Destroys merozoites.
(iii) Paludrin, Sulphadoxin

Destroys all stages of Plasmodium in blood and liver.

Note : Though this drug is very effective even then rarely used, because this drug may damage liver.
(iv) Daraprim
Daraprim destroys gametocytes of the Plasmodium
(v) Nevaquin
(vi) Melubrin
(vii) Resochin
(viii) Reziz
(ix) Reziz forte
(x) Primaquin - Destroys all stages of Plasmodium.

Malaria vaccine

No effective malarian vaccine has been developed till date.Reason :
Because antibodies for malarian parasite (Plasmodium) do not develop in blood. Since Plasmodium does
not induce production of host’santibodies and because it has many resevoir hosts. the eradication of
Plasmodium is virtually impossible.

4. SPECIAL POINT
(i) Author of malarian parasite monograph is Garnham.
(ii) Plasmodium is also called Haemosporidian, because it is found in human blood.
(iii) Infection of malaria takes place by 4 ways-
(a) Through infection of sporozoite
(b) Through blood donation
(c) Through infected needle
(d) Through placenta to the (faetus) baby
(iv) Malaria is an insect borne disease this statement was given by Ronald Ross.
(v) In malaria infected person, best time to treat malaria is during starting of fever with shivering.
(vi) Post erythrocytic phase of Plasmodium is resistant to drug.
(vii) Contractile vacuole remain absent in Plasmodium because isotonic environment is found around the
Plasmodium.
(viii) In India, maximum cases of malaria is found in Karnataka.
(ix) During malarial fever body temperature may go upto 106ºF.
(x) Vector control research centre is in Pondicherry (Tamilnadu).
(xi) Sir Ronald Ross was doctor in Indian Army of British origin. He lived in India at Hyderabad.
(xii) Gametocyte of Plasmodium is also called Gamont.
(xiii) In malaria, number of lymphocyte in blood of the infected person becomes very high.
(xiv) Lysolecithin destroys membrane of the RBC.
(xv) Spleen is the store house of malarian parasite in human body.
(xvi) Everyday 5% of RBC get destroyed by malarian parasite.