Plasmodium: Lifecycle |Disease |Symptoms |Prevention |Treatment
- Phylum- Protozoa
- Sub-phylum- Plasmodroma
- Class- Sporozoa
- Sub-class- Telosporidia
- Order- Haemosporidia
- Genus- Plasmodium
Malaria is one of the serious diseases of human beings occurring in Japan, U.S.A., China, India, Philippines, South Africa and Mexico in epidemic form. It is caused by a species of Plasmodium, transmitted through the bite of female Anopheles mosquito. Man is the principal host while mosquito is the secondary or intermediate host.
Four species of Plasmodium are reported to cause different types of malaria in human beings, viz., P. vivax, P. ovale, P. malariae and P. falciparum. In human beings Plasmodium attacks the R.B.C. and liver cells and releases a toxic substance “Haemozoin” which causes malaria. Malaria is identified by periodic attack of high fever. Death of man is not actually directly due to the parasite but parasites make the patient weak, causing anaemia ultimately resulting in death.
When a female Anopheles, containing sporozoite stage of Plasmodium in her salivary glands, bites a man, the sporozoites are released into the blood stream of human beings. After 3 days of entrance these sporozoites start dividing in the parenchyma cells of the liver and attain schizont stage. Now these schizonts attack the R.B.C. and get changed into trophozoites. Now trophozites of each R.B.C. attain schizont stage and divide into 6 to 36 daughter merozoites. Due to the high pressure R.B.C. ruptures and releases the merozoites into the blood plasma. These merozoites attack the other R.B.C. After 10 days the number of parasites becomes large and they produce toxins which cause fever in man.
There are four recognized forms of malaria caused by different species of Plasmodium:
- Tertian malaria: It is caused by P. vivax in which fever is repeated every third day.
- Ovale malaria: It is caused by P. ovale in which fever is repeated every third day.
- Quartan malaria: It is caused by malariae in which fever is repeated every fourth day.
- Malignant malaria: It is caused by falciparum in which fever is repeated every second day and is fatal to the patient.
- Quotodian malaria: It is caused by mixed infection of the above mentioned species, so continuous fever is observed.
After schizogony some merozoites attain gametocyte stage and remain in the human blood without any further development. If per chance any female Anopheles bites the person containing gametocytes, the macrogametocyte becomes macrogamete known as female gamete. The microgametocyte forms 6 to 8 microgametes. It is notable that if any stage other than gametocyte is sucked by the mosquito it gets digested in the gut of the mosquito and there is no chance for further infection. After fusion, the zygote is formed in the stomach of mosquito which by penetrating the gut wall reaches outside the gut and gets converted into oocysts. After one week the oocyst is changed into sporozoites which go to the salivary gland of the female mosquito and are transferred to the body of the man by the bite of the mosquito and thus completes its life cycle in man and mosquito. Although malaria had been already eradicated from our country but these days the increasing infections by this parasite are resulting in the return of malaria again.
Signs and Symptoms (Pathology):
The pathology of malaria is related to the symptoms and damage caused by the parasite in human-beings. The pathological details differ with the species of Plasmodium and even with the particular strain infecting a victim. The individuality, conditions and even genotype of the host probably play important role as does immunity. In the case of severe infection, the number of erythrocytes has been found to be reduced to one fifth of the normal count. The agglutination of red blood cells in P. falciparum infection and loss of plasma within the blood vessels in all types of malaria cause the so-called ‘sludging’ of the corpuscular elements in the blood vessels. As result of such sludging there is: (i) A progressive decrease in the erythrocytes, therefore, reduction in the oxygen, hence oxygen starvation of tissues occurs, (ii) Multiple thrombosis in smaller blood vessels, (iii) Progressive decrease in circulating blood volume.
In case of falciparum malaria the brain is congested, the capillaries increase in number and become swollen due to hemostasis and hemorrhage from retinal vessels is relatively common.
The parasitized red blood cells accumulate in the sinuses of the spleen, liver and bone marrow. The spleen is typically enlarged, congested, become soft and hemorrhagic in primary stage and further becomes hard in chronic phase. As the quantity of hematin increases, its colour darkens. The liver becomes hypertrophic and congested in acute malaria and its colour index is greater than normal. The bone marrow undergoes similar changes as the spleen but to lesser degrees. In addition, the production of granulocytes is reduced and erythropoiesis is increased to meet the deficit in functioning red blood cells. The kidneys are congested, the glomerular capillaries become thrombotic with the accumulation of parasitized red blood cells, free hematin and wandering macrophages. The adrenals may be damaged by hemorrhage or affected by general toxemia.
Thus, the release of toxic substances due to the brushing of cells may trigger a response in the temperature regulating mechanism of the body. The subjective chill is due to the damage of the nervous centre involved. The fever has its own effect, similar to other fevers. Anaemia naturally results from the destruction of the blood cells.
Prevention and control:
In the prevention of malaria the main objective should be the reduction of the Anopheles below the transmission level and at the same time to save human beings from mosquito bite. The following measure may be suggested:
- Treatment of human infections: It is well known that the gametocytes are the stages for continuation of the life cycle of Plasmodium when ingested by Anopheles. The patients are the carrier of the gametocytes. Primaquine is very much effective in terminating exo-erythrocytic infection and hence gametocyte production.
- Measure against adult mosquitoes: The adequate screening of houses and use of mosquito nets may protect human beings against mosquito bite to a greater extent. The use of repellents on exposed parts of the body may protect man for few hours from mosquito bite. The use of pyrethrum and other effective insecticides may kill the adult mosquitoes.
- Measures against mosquito breeding: Mosquitoes breed in pools, ponds, irrigation canal, seepage channels, swampy area etc., therefore, it is important to eliminate or keep the minimum aquatic vegetation in which female lays eggs and hatched larvae develop into pupae. If drainage is not possible, the introduction of Gambusia may control by feeding upon the larvae the moment they are hatched. The development of such natural conditions which are unfavourable for Anopheles breeding, for e.g. removal of dense vegetation and development of shade because Anopheles requires sun shine. The larvicidal control is universally applicable technique to reduce mosquitoes.
Some of the anti-malarial drugs are:
- Cincona products: Quinine : Quinine sulfate is administered orally and quinine dihydrochloride is given intravenously to destroy asexual parasites in circulating erythrocytes.
Totaquine: It is economic and administered orally for the treatment of malaria infected persons.
- Acridine compounds : Quinacrine: Quinacrine hydrochloride is effective in case of falciparum infection and quartan malaria. Its proprietary names are Atabrine and Atebrin.
- Aminoquinolines: Chloroquine: Chloroquine diphosphate dihydrate is administered orally for the treatment of malaria. Chloroquine hydrochloride is used for parenteral use. It is lethal to asexual stages of Plasmodium in circulating red cells. Its proprietary name is Aralen.
Amodiaquin : Dihydrochloride dihydrate is taken orally and is very much effective against asexual stages of Plasmodium in red cells.
- 8-Aminoquinolines : Primaquine sterilizes the gametocytes of falciparum malaria. Pentaquine reduces the relapse rate in vivax infections. Primaquine is least toxic than others and its action is primarily against fixed tissue stages of vivax
- Primidine compounds : Daraprim when administered in suppressive doses, it quickens the action of the drug in all the species of malarial parasites.
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