WATCH THIS VIDEO FOR THE MOSQUITO PHASE OF PLASMODIUM VIVAX http://www.youtube.com/watch?v=RqRuSwZey_U
THE MOSQUITO PHASE – ROSS CYCLE
LIFE CYCLE OF PLASMODIUM VIVAX IN MOSQUITO
Mosquito phase of plasmodium vivx starts with the entry of gametocytes. When female anapheles mosquito sucks the blood of malaria patient , the gametocytes along with the other stages of plasamodium vivax that occur in human host enter the crop of mosquito. In the crop except gametocytes all others are digested. Since the pH in the crop and body temperature are favourable , the life cycle is continued further and it includes the folowing stages :
3)Formation f oocyst
The formation of male and female gametes from the gametocytes is called gametogony.It occurs in the lumen of the crop of mosquiuto.
The gametogony in plasmodium vivax include
FORMATION OF MALE GAMETES
FORMATION OF FEMALE GAMETES.
FORMATION OF MALE GAMETES: During this process the nucleus of microgametocyte undergoes thre mitotic divisionsforming eight daughter nuclei called pronucei. They move towards the periphery.The cytoplasm pushed out in the form of eight flagella like processes. Into each flagellum like process, one pronucleus enters and forms a microgamete or male gamete. These male gametes show lashing movements like flagella and get seperaedfrom the cytoplasm of microgametocyte. This process is called EXFLAGELLATION.
FORMATION OF FEMALE GAMETES: the femalegametocyte ( Macrogametocyte) undergoes a few changes and transform in to a female gamete. This process is called MATURATION. During this process the nucleus of the female gametocyte moves towards the periphery and the cytoplasm at that point forms a projection. This projected region is called the fertilization cone. This is the point of entry of male gamete.
The fusion of male and female gametes is called fertilization. It alsooccurs in the lumen of the crop of the mosquito. When one of the actively moving male gamete comes into contact with the fertilization cone of the female gamete, it enters into the cytoplasm of female gamete.
The pronuclei and the cytoplasm of these two gametes fuse with each other , resulting the formation of the zygotic nucleus – synkaryon. The female gamete with synkaryon is now called zygote.
Since, the morphologically dissimilar male and female gametes fuse to form a zygote , the process is known as Anisogomy.
3) FORMATION OF OOCYSTS:
The zygote remains inactive for some time and then transform into a long , slender, motile, vermiform, structure called ookinete or vermicule within 18 – 24 hours. It pierces the wall of the crop and settles beneath the basement membrane. It becomes round and secretes a cyst around its body. This encysted ookinete is now called oocyst. About 50 – 500 oocysts are formed on the wall of the crop and appear in the form of small nodules . Sir Ronald Ross identified thee oocsts for the first time.
Above three staes viz., zygote, ookiknete and oocyst are the diploid stages and all others are haploid. Ookinete is only motile diploid stage.
The formation of sporozoites in the oocysts is called sporogony. According to Bano , the nucleus of the oocyst first undergoes reduction division followed by repeated mitotic divisions
resulting in the formation of about 1,000 daughter nuclei. Each bi of nucleus is surrounded by a little bit of the cytoplasm and transforms into a sickle shaped sporozoite. Oocyst with such sporozoites is called sporocyst. When this sorocyst ruptures , the sporozoites are liberated into the haemocoel of the mosquito. From there, they travel into the salivary glands and are ready for infection.
The life cycle of Plasmodium in mosquito is completed in about 10 – 24 dys.
Plasmodium vivax causes benign tertian malaria and the fever recurs after every 48 hours. . The clinical symptoms of this diease include bouts of fever which can be expressed in three stages namely ,
1) COLD STAGE
2) HOT STAGE
3) SWEATING STAG.
1) COLD STAGE: Chills, shivering , headache and giddiness.
2) HOT STAGE : High temperature of the body , rapid breathing and an increase in the pulse rate.
3) SWEATING STAGE: Profuse sweating followed by lowering of the body temperature to the normal level.
Anaemia and Splenomegaly are noticcced in a chronic malaria patient. Relapse of malaria may also be noticed some times.
RELAPSE OF MALARIA: Some of the stages of macro- metacryptozoites may survive for a long period in liver as dormant stages called hypnozoites. Reactivtion of these hypnozoites leads to the initiation of fresh erythrocytic cycles resulting in the new attacks of malaria. This is referred to as relapse of malaria.
Malaria can be cured by Quiine which is an alkaloid extracted from the bark of Cincona officialis.
The spread of Malaria can be controlled by the following methods.
1) Avoiding mosquito bite by using mosquito nets , mosquito rerpellents , etc.,
2) Killing the adult mosquitoes by spraying of DDT, BHC , etc., in the house dwellings.
3) Killing the mosquito larvae by sprying of kerosene , pyrethrum oil , etc., on stagnant water.
4) Introduction of larvivorous fishes like Gambusia , Insectivorous plants like Utricularia into the places where mosquitoes breed. It is the biological controll method to avoid the growth of mosquito larvae.