Plasmodium vivax or Malarial parasite is an intracellular blood parasite of man which causes malaria in human being.
Phylum – Protozoa
Class – Sporozoa
Order – Haemosporidia
Genus – Plasmodium
Species – vivax
Charles Laveran (1880) discovered Plasmodium in the blood of a malarial patient. In the year 1895 Ronald Ross, an Indian army doctor discovered the oocyte of plasmodium in the stomach of the female anopheles mosquito.
The life cycle of plasmodium is completed inside the body of the two hosts such as male and female anopheles mosquito. Hence, the life cycle is digenetic. Man is the primary or definitive host and female anopheles mosquito is the secondary or intermediate host or vector.
Mode of Infection:
When an infected female anopheles mosquito bites a healthy person to suck blood, it injects the sporozoites (infective stage) into the human blood along with its saliva. Sporozoites are inoculated in thousands into the human blood. Asporozoite is microscopic, slender and sickle shaped animalcule.
Its body length is about 14 μ and breadth is 1μ Body is covered by a thin, elastic cuticle which gives a definite shape to its body (Fig. 6(A). 1). In the absence of any locomotory organelles the sporozoites show gliding movement. Two secretory glands are present at the anterior ends which are believed tso help in penetration into the cell.
Life Style (Fig. 6(A).5):
The asexual life cycle in man is called schizogony. It is divided in to 3 phases (a) Pre-erythrocytic schizogony, (b) exo-erythrocytic schizogony, (c) erythro-cytic schizogony. The sporozoite is the infective stage. While sucking blood an infected mosquito injects the sporozoites into the body of man. The sporozoites enter the liver to carry on pre and exo-erthrocytic schizogony.
Through these two cycles large number of merozoites is produced. They enter R.B.C. to carry on erythrocytic schizogony. This erythrocytic cycle is repeated in every 48 hours which coincides with the appearance of the symptoms of malaria. Some of the merozoites produced by erythrocytic cycle never attack fresh R.B.C. They wait for the mosquito to be sucked. They are of two types: male and female gametocytes. They carry on sexual reproduction inside the stomach of mosquito.
The sexual part of the life cycle occurs in the body of mosquito in low temperature. After entering into the stomach of mosquito, the male or microgametocyte produces 4-8 microgametes. This process occurs through exflagellation. The female or macrogametocyte produces only one macrogamete. A microgamete fuses with a macrogamete to form zygote. The zygote gives rise to an elongated ookinete which penetrates through the stomach wall of mosquito. The ookinete then changes into a spherical oocyst. The occyst divides to form sporoblasts. Each sporoblast produces large number of sporozoites. This process is known as sporogony. When the infected mosquito bites a healthy man the sporozoites are injected along with the saliva.
Types of Malaria:
Four species of Plasmodium cause malaria in human beings. Each species has specific incubation period, period of recurrence and harmful effects on the host.
1. Benign Tertian Malaria:
It is also simply called as tertian malaria. As it is caused by P. vivax, it can be called as Vivax malaria. Here the incubation period is 14 days and the recurrence of fever is after every 48 hours i.e. every third day. In this type of malaria, the death rate is low.
The incedence of the disease is worldwide but very common in temperate regions. It is the most common type of malaria in India.
2. Quartan Malaria:
It is also called as subclinical malaria and is caused by P. malariae. Here the incubation period is 28 days and the recurrence of fever takes place every 72 hours i.e. every fourth day. It is ordinarily not fatal and untreated persons can live a long life like normal human beings. It is common in tropical Africa, Sri Lanka and Burma but less common in India.
3. Mild Tertian Malaria:
It is also known as ovale malaria as it is caused by P. ovale. This type of malaria resembles to tertian malaria. Here the inclubation period is 14 days and the fever recurs every 48 hours or third day. This malaria is not very common and is mainly confined to tropical Africa.
4. Malignant Tertian Malaria:
It is also called as pernicious malaria or Aestivo- automnal malaria and is caused by P. falciparum. Here the incubation period is 12 days and the recurrence of fever occurs every 48 hrs. i.e. every 3rd day. Death rate is highest in this type as the fever leads to various complicated conditions. Sometimes due to multiple or mixed infections by more than one species of Plasmodium the fever recurs almost daily and this condition is known as Quotidian Malaria.
The treatment of malaria by inoculations or vaccinations is not possible as the parasite does not produce antibodies or antitoxins in human blood. Long back quinine was used as an effective antimalaria drug to kill the schizonts but it had several disadvantages. Later Atebrin and camoquin were used in Germany. At present the successful antimalaria drugs include chloroquine, paludrine, plasmochin, resochin, Daraprim which destroy the schizonts and gametocytes.
Malaria can be prevented by adopting following measures:
(i) Use of drugs:
Healthy persons living in malarious regions should take small regular doses of preventive medicines (Atebrine 0.1 gm per day, Chloroquine 0.15 gm once a week).
(ii) Defence against mosquito bites:
(a) Mosquito net should be used especially during night.
(b) House should be constructed on dry high ground away from marshy places having good drainage system.
(c) Anti-mosquito cream (e.g. Odomus) mosquito repellants, mustard oil, dimethyl carbamate should be applied over exposed parts.
(d) Susceptibility to infection can be minimized by taking proper nourishment, by avoiding exposure to bad conditions.
A large number of people die of malaria every year in India. To control and eradicate malaria a nationwide programme NMEP (National Malaria Eradication Programme) has been launched.
(a) To control malaria adult Anopheles mosquitoes are destroyed by spraying insecticides like D.D.T., Gammaxene, Flit, Pyrethrum etc.
(b) Mosquitoes can be driven out of the house or killed by fumigation, sulphur, pyrethrum, tarcomphor and other derivatives of naptha are burnt to produce poisonous fumes. In Municipal areas fumes are produced by TIFA machine.
(c) The mosquito larvae and pupae grow in stagnant water. Swampy areas, marshes and stagnant water should be drained off to eliminate breeding grounds. The bashes and shrubs near the house should be cleared.
(d) It is easier to kill the aquatic larvae than the winged adults. The larvae in the stagnant waters are prevented from growing by cleaning drains, streams, ditches etc.
(e) By introducing mosquito larvae eating Fishes like Gambusia, Gold fish, Stickle backs, Minnows, Trouts etc. ducks in ponds, ditches, tanks the larvae population can be reduced. This is known as Biological control (Fig. 6 (A).3).