PLASMODIUM VIVAX


PLASMODIUM VIVAX

PHYLUM           : PROTOZOAsir ronald ross

SUB PHYLUM  : SPOROZOA

CLASS                : TELOSPORIA

SUB CLASS       : COCCIDIA

ORDER              : EUCOCCIDIA

GENUS               : PLASMODIUM

SPECIES            : VIVOX

             Plasmodium vivax is a cytozoic , pathogenic , digenetic and most widely distributed protozoan parasite. It occurs in the liver cells and RBCs of human beings causing benign tertian malaria. Its primary host is the female Anapheles Mosquito and the secondary host is man. Reservoir host is monkey. The infective stage is sickle shaped sporozoite and the mode of infection is inoculation.

   Four species of Plsmodium cause four types of malaria in man. They are

morphological differences-plasmodiumspecies

1.Plasmodium vivox –  benign tertian malaria.   

2.Plasmodium falciparum  – malignant tertian malaria or cerebral malaria.

3.Plasmodium ovale – mild tertian malaria.

4.Plasmodium malariae – quartan malaria.   

              Off all these four species , Plasmodium vivox is the most common and most widely distributed malaria parasite. Hence its life cycle along with pathogenicity , treatment and preventive measures are briefly described here.

HISTORY OF MALARIA

1.The term Malaria is taken from two Italian words Mala and aria which means “bad air” as it was thought that malaria was due to foul air produced in marshy lands.

2.The word malaria was coined  by Macculoch in 1827. 

3.Charles Laveron , a French military doctor ,first observed the parasite in the blood of malaria patient  in 1880.

4.Camilo Golgi an Italian scientist , observed the malarial parasite in the red blood cells of malarial patients in 1885.

5.Richard Pfiffer , a German doctor said that the malaria may spread by blood sucking insects.

6.Sir Patric Manson, a Scottish doctor discovered that the filariasis  is spread through female culex mosquitoes in 1894.

7.Sir Ronald Ross , british army doctor working at secunderabad  discovered  oocysts of plasmodium in the crop wall of female anopheles mosquito on 20th august 1897. For this discovery, he was awarded Nobel prize in the year 1902.

              In recognition of this famous work of ross, 20th  august of every year is celebrated as world malaria day or world mosquito day.

8.G.B Grassi and others have described the life cycle of  Plasmodium vivax in the female Anopheles mosquito in 1898.

9.Garnham published a detailed monograph on Plasmodium vivax in 1966.                                

Structure of sporozoite:

p.vivax-sporozoite-2

1   1.The infective stage of malaria parasite to humanbeings is sporozoite.

    2.The sporozoite occurs in the salivary glands of female anopheles mosquito.

    3.The structure of sporozoite was described by Garnham 1963.

    4.The sporozoite is sickle shaped with a swollen moddle part and pointed at both ends of its body.

    5.It measures about 15 microns in length and 1 micron in width.                                                        

6  6.The body is covered by an elastic pellicle with Microtubules which help in the wriggling movements of the sporozoite.

    7.The cytoplasm is granular with cell organelles such as Golgi complex , endoplasmic reticulum, mitochondria and a nucleus.

    8.The cytoplasm also shows many convoluted tubules of unknown function throughout the length of the body.

    9.It shows a cup like depression called apical structure  at the anterior end which helps in adhesion.

    10.    A pair of narrow tubular structures called secretory organelles  open into the apical cup. They secrete a cytolytic enzyme, which helps in the penetration of sporozoite into the liver cells.    

 LIFE CYCLE OF PLASMODIUM VIVAX

         The life cycle of plasmodium vivax includes two hosts viz., the primary and secondary hosts.

                  The primary host is the female Anopheles mosquito, in which the parasite completes the sexual part of the life cycle without causing any disease. This part of the life cycle is called cycle of ross  in the honour of sir Ronald Ross. Mosquito is also the vector host.

                   The secondary host is the human being. In human  being , asexual part of the lifecycle is completed by causing disease. Thispart of the life cycle is called Golgi cycle in the honour of  Camillo Golgi .

           The reservoir host of malarial parasite is monkey.

HUMAN PHASE OF LIFE CYCLE:p.vivax-humanphage-2

In man, the plasmodium vivax reproduces asexually by multiple fission called schyzogony. It occurs in the livercells (hepatocytes) as well as in R.B.C. In liver cells, it is called hepatic schyzogony and in RBC it is called erytrocytic schyzogony.

Hepatic schyzogony:

p.vivax-illustration abt stages p.vivax-pictures

             The hepatic schyzogony of plasmodium vivax was discovered by Shortt and Garnham. Whenever , a mosquito infected by plasmodium bites a man , nearly 2000 sporozoites  are released into the blood of man through its saliva . Within half an hour , they reach the hepatocytes where they undergo  pre-erythrocytic  and erythrocytic  cycles.

Pre-erythrocytic cycle :

p.vivax-human phage

1.   Sporozoites are the infective stages of plasmodium to man.

2 .   Whenever the sporozoites reach the liver cells , they transform into trophozoites.

3.   They feed on the contents of the heparic cells  and attain the maximum size. This stage is called schizont.

 4.     The nucleus of schizont divides several times mitotically, followed by the cytoplasmic divisions  reaulting in  approximately 12,000 daughter individuals called cryptozoites or the 1st generation merozoites.

 5.   The cryptozoites enter the sinusoids of liver by rupturing the cell membrane of the schizont and the liver cells.

 6.   This entire process is completed approximately in 8days. 

 7.   Now these cryptozoites have two options i.e., they can enter either fresh liver cells and continue exo-erythrocytic cycle or they can enter RBC and continue erythrocytic cycle.

Exo-erythrocytic cycle:

1                 If the cryptozoites enter the fresh liver cell, it transforms into a trophozoiteand feeds on liver cell.

        1.   After attaining maximum size it undergoes multiple fission and results the second generation merozoites called matacryptozoites.                                                      

    2.   Metacryptozoites are of two types – the smaller micro-meta cryptozoites and larger macro-metacryptozoites.

    3.   This entire process is completed approximately in two days.

    4.    The macro-metacryptozoites attack fresh liver cells and continue another exo-erythrocytic cycle. Where as the micro-metacryptozoites always enter blood stream and attack fresh RBC to continue erythrocytic cycle.

Prepatent period:

  The  interval between the first entry of plasmodium into the blood in the form of sporozoites and the second entry of plasmodium in the form of cryptozoites is called prepatent period. It lasts approximately 8 days  During this period, the host does not show any clinical symptoms of the disese . It is only a means of multiplication.

  Erythrocytic cycle:

p.vivax-3

1.   The erythrocyic cycle of plasmodium vivax was first described by Camillo Golgi.Hence it is also called Golgi cycle.

2.   This cycle is initiated either by the cryptozoites of pre-erythrocytic cycle or the micro-metacryptozoites of exo-eryhrocytic cycle.p.vivax trophozoite

3.   In the fresh RBC , these staes assume spherical shape and transform into trophozoites.                                                                          p.vivax-ring stage

4.   The trophozoite develops a small vacuole which gradually enlarges in size , pushing the p.vivax -late ring stagecytoplasm and nucleus to the periphery. Now the Plasmodium looks like a finger ring. Hence this stage is called signet ring stage.p.vivax-early ring

5.  Soon it looses the vacuole, develops pseudopodia and becomes amoeboid stage.

6.   With the help of p.vivax-amoeboid stagepseudopodia, it actively feeds on the contents of the RBC and increases in size. As a result, the RBC grows almost double the size. This process is called Hypertrophy.

7.   The malaria parasite digests the globin part of the ingested haemozoine granules in fod vacuole of plasmodiumhaemoglobin and converts the soluble haem into insoluble crystalline haemozoin. It is called the malaria pigment which is a disposable product.

8.   During this stage , small red cooured dots appear in the cytoplasm of the RBC  known as Schuffner’s dots.These are believed to be the antigens released by the antigens released by the parasite.

9.   Now the Plasmodium loses the p.vivax-schizontpseudopodia, further increases in size, occupies the entire RBC and becomes a schizont.

10.                The Schizont undergoes p.vivax-rosetteschizogony and produces 12 to 24 erythrocytic merozoites. They arranged in the fom of the petals of a rose in the Rbc. Hence this stage is called the Rosette stage.

11.               Finally the erythrocyte bursts and schizogony in RBCreleases the merozoites along with haemozoin ino the blood.

12.               This cycle is completed approximately in 48 hours.       

haemozoine

haemozoine in blue

      

haemozoine crystals

                                                                                                                                                                                           Incubation period:

      The incubation period between the entry of Plasmodium    into the blood in the form of sporozoite and first appearance of symptom of malaria in man is called incubation period. It is approximately 10-14 days.

FORMATION OF GAMETOCYTES :

           In human beings as erythrocytic cycles are repeated several times, a decrease in the number of RBCs sets in.

     Due to this, parasites may not be able to survive further. Hence some of the merozoites instead of continuing the erythrocytic cycle transform into gametocytes. The gametocytes are formed in the spleen and matured in the  bone marrow.Gametocytes are of two types , namely

     A.  Microgametocyte,    

microgametocyte

microgametocyte

     B.   Macrogametocyte.

      Microgametocytes are small in size, with a large central nucleus and form the male gamete. Macrogametocytes are

microgametocyte

microgametocyte

larger in size with a small eccentric nucleus an granular cytoplasm.

        In human beings, the lifecycle does not continue after the formation of

macrogametocyte

gametocytes. The gametocytes donot develop as the conditions like body temperature and PH  of blood in man are no favourable. These conditions favour their further development in mosquito. Hence if they fail to reach mosquito , they degenerate and die in about one week time.

Advertisements

About balarangaiahnarapuram

TEACHER M.Sc in ZOOLOGY M.Sc in PSYCHOLOGY B.Ed
This entry was posted in BIOLOGY IN HUMAN WELFARE, INTERMEDIATE -EM -1 and tagged , , , . Bookmark the permalink.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s