Plasmodium vivax( MALARIAL PARASITE)

Department of Zoology

Govt. Degree College, Basohli

Shiv Kumar

Asstt. Prof. in Zoology

The most interesting sporozoan genus is plasmodium

Because of their malaria causing abilities , these species commonly

referred as malarial parasites

All resides in the RBC

Mosquitoes are the vectors

The Malarial parasite

4 species are known to cause different types of malaria

P. vivax, P. ovale, P. malariae and P. falciparium

Geographically distributed in tropical and temperate countries

P. vivax is most commonly distributed and prevails in the

temperate regions of the world.

Life Cycle of P. vivax

• P. Vivax is the most common of the human infecting malaria fever

parasites.

• Causes benign tertian or vivax malaria, characterized by a 48 h

cycle b/w first fever and subsequent chills and fever.

• Hosts: diagenetic

a. Man:

asexual cycle in two phases

First in liver – liver schizogony

Second in RBC – erythrocytic schizogony and forms gametes

b. Mosquito:

Sexual cycle is completed in female anopheles

It involves gametogony and sporogony

Asexual cycle of P. vivax in man

[1]. Infection

• Anopheles bite resulting in the inoculation of thousands of sporozoites

along with saliva into the persons body (victim)

[2]. Sporozoites

• Infective form of parasite

• Small, spindle shaped measuring about 11-12 µ in length and 0.5-1 µ

in width

[3]. Liver Schizogony

• After 30m of infection, sporozoites invades hepatic tissues and multiply

by schizogony in two phases (pre and exo-erythrocytic)

a). Pre-erythrocytic phase

• Sporozoite becomes cryptozoite in hepatic cells and becomes spherical

and non-pigmented schizont.

• Undergo multiple fission (schizogony) and forms numeros uninucleate

cryptomerozoites

• At the end of phase, hepatic cell bursts and cryptomerozoites are

liberated.

b). Exo-erythrocytic phase

• Cryptomerozoites enter new liver cells and becomes metacryptozoites

• Undergo similar schizogony and produces metacryptomerozoites.

[4]. Erythrocytic schizogony

• Micro metacryptomerozoites invades RBC and starts erythrocytic

schizogony and includes following stages:

a). Tropozoite stage

• Inside RBC, micro metacryptomerozoites becomes rounded and

modified into trophozoite.

b). Signet ring stage

• Trophozoite grows, develops vacuole and clinically referred as

signet ring stage.

c). Amoeboid stage

• Meanwhile signet stage develops into active amoeboid trophozoite

• At this stage, samle red eosinophilic granules appear in the

cytoplasm –schuffners granules

d). Schizont

• Amoeboid trophozoite after feeding becomes rounded, grows in

size and becomes schizont

• It undergoes schizogony and forms merozoites

• One erythrocytic cycle takes 48h

[5]. Post-erythrocytic schizogony

• Sometimes merozoites reach the liver and undergoes schizogonic

development in the liver cells –post-erythrocytic schizogony.

[6]. Formation of gametes

• Merozoites increases in size to become rounded gametocytes.

• Male – microgametocyte and female- magagametocyte

• Gametocytes donot devide but remain as intracellular parasite

until they either die or ingested by vector

Sexual cycle of P. vivax in man

[1]. Ingestion by mosquito

• Female anopheles gets the infection by sucking the blood of infected

person

• RBC are digested and gametocytes are liberated and lodged into the

cavity of the gut.

[2]. Gametogony

• Development of gametes (Haploids) from gametocyte – gametogony/

gametogenesis.

• Gamtes are of two types

a). Microgametes

• Male or microgamete undergoes exflagellation in the midgut of mosquito

• Each nucleus divides by mitosis and produce 6-8 haploid daughter and

assemble at periphery

• Cytoplasm outgrows into long thin flagella like projection and later these

projections break away as mature male gamete

b). Megagametes

• Female megagametocyte undergo some reorganisationa nd becomes a

female gamete, which is ready for fertilization.

[3]. Fertilization

• Megagamete gives out a cytoplasmic projection – fertilization cone.

• Microgamete attached to this cone and transfer its nucleus to

megagamete

• Fertilization or syngamy takes place

• Diploid zygote forms

[4]. Ookinete

• After sometime zygote becomes active and shows gliding moment and is

k/as ookinete

• It measures about 15-22 micron in length and 3 micron in width.

• It attaches itself to peritrophic membrane of gut.

[5]. Encystment

• Ookinete penetrates through walls of midgut, becomes spherical and

begins enyst.

• The encysted zygote – oocyst / sporont

[6]. Sporogony

• Oocyst enters into a phase of asexual multiplication- sporogony

• Firstly divides by meosis and then by mitosis and forms enormous

haploid nuclei surrounded by cytoplasmic masses

• The daughter nuclei arrange themselves along the margin of

cytoplasmic masses and later forms slender finger like processes

having single nuclei in each

• In this way about 10,000 minute slender and sickle bodies are

formed-sporozoites .

• When sporozoite matures oocyst ruptures and liberated into

haeomocoel later penetrates into salivary glands

• Whole sexual cycle completes into 0-12 days

• Now mosquito becomes infective

Pathogenesis of malarial parasite

Symptoms of malaria first appear several

days after the infection of the parasite.

This time – incubation period

Each attack of fever shows three stages:

1. Cold Stage

• At the onset of malaria patent suffers

from severe shaking chill.

• Cold stage lasts for 20 min

2. Hot stage

• As the chill subsides, the body temp rises

as high as 106°F. and lasts for 1-4 h.

3. Sweating stage

• As the temp lowers down, patent sweats

profusely.

• Fever comes down and temperature

becomes normal

Malaria fever occurs when schizont in RBC bursts and set free

their merozoites and malarial pigment haemozoin in the plasma.

Anemia is inevitable due to:

• Destruction of RBC

• Infected RBC become more fragile and rupture easily

• Parasite produce haemolysin- brings haemolysis

• In chronic case- spleen becomes enlarged

Control of Malaria

Control Measures falls into three categories:

1. Elimination or destruction of vector

2. Prophylaxis (prevention of infection)

3. Treatment of infected patents

[A]. Destruction of anopheles

Most effective and surest way of controlling malaria and can be

done through

• Destruction of adult mosquitoes: method used are killing of

hands, traps, fumigation, spraying and sterilization .

• Elimination of breeding places: swampy, marshy and water

logging areas are cleared out, bushes and shrubs are cleared

off etc.

• Destruction of larvae and pupae of mosquito through proper

drainage (Flowing water), oil screens, chemical larvicides and

biological methods.

[B]. Prevention of infection

• Through the use of insect repellent, nets, gloves and by

screening bedroom windows.

[C]. Treatment

• Chlorquine and quinine: anti-erythrocytic stage drugs.

• Primaquine and pyrimethamine: anti-exoerythrocytic stage

drugs.