Malaria (Malaria fever) : Causes, Pathogenesis, Symptoms, Diagnosis, Treatment & Prevention
Definition :
- Malaria (Malaria fever) is a protozoal disease caused by any one or combination of 5 species of Plasmodium : Plasmodium falciparum, P. vivax, P. ovale, P. malariae and P. Knowlesi .
- Plasmodium falciparum causes Malignant malaria, whereas rest of species produce Benign form of illness.
- All forms of Plasmodium are transmitted by the bite of female Anopheles (Anopheline) mosquitoes, and humans are the only natural reservoir.
Pathogenesis :
The life cycle of plasmodia is complex.
- The female anopheline mosquito becomes infected when it feeds on human blood containing gametocytes, the sexual forms of the malarial parasite . Development in the mosquito takes from 7 to 20 days, and results in Sporozoites accumulating in the salivary glands.
- As mosquitoes feed on human blood, sporozoites are introduced into blood stream ( from the saliva ) and within a few minutes infect liver cells. Here the parasites multiply rapidly to form a Schizont containing thousands of merozoites.
- After a period of days to several weeks that varies with the Plasmodium species, the infected hepatocytes release the merozoites, which quickly infect red cells.
Red cells infected with malaria are prone to haemolysis. This is most severe with P. falciparum, which invades red cells of all ages but especially young cells; P. Vivax and P. ovale invade reticulocytes, and P. Malariae normoblasts, so that infections remain lighter. - Intraerythrocytic parasites either continue asexual reproduction to produce more merozoites or give rise to gametocytes capable of infecting the next hungry mosquito.
- During their asexual reproduction in red cells, each of the four forms of malaria develops into trophozoites with a somewhat distinctive appearance.
- Thus, the species of malaria that is responsible for an infection can be identified in appropriately stained thick smears of peripheral blood.
- The asexual phase is completed when the trophozoites give rise to new merozoites, which escape by lysing the red cells.
P. vivax and P. ovale may persist in liver cells as dormant forms, hypnozoites, capable of developing into merozoites months or years later. Thus the first attack of clinical malaria may occur long after the patient has left the endemic area, and the disease may relapse after treatment if drugs that kill only the erythrocytic stage ofthe parasite are given.
P. falciparum and P. malariae have no persistent exoerythrocytic phase but recrudescence of fever may result from multiplication of parasites in red cells which have not been eliminated by treatment and immune processes.
Note :-
- P. falciparum has influenced human evolution, with the appearance of protective mutations such as sickle cell HbS, thalassaemia , G6PD deficiency and HLA-B53.
- P. falciparum does not grow well in red cells that contain haemoglobin F, C or especially S. Haemoglobin S heterozygotes (AS) are protected against the lethal complications of malaria.
- P. vivax cannot enter red cells that lack the Duffy blood group; therefore many West Africans and African- Americans are protected.
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Clinical Symptoms :
- The clinical features of malaria are non-specific . Some of the clinical symptoms which are shown by infected persons are as follows :
– Episodic shaking, chills, fever & Rigor
– Severe anemia ( Hemolytic anemia )
– Massive splenomegaly and occasional hepatomegaly
– Fever (Temperature of non-immune individuals and children often rises above 40°C (104°F) in conjunction with tachycardia and sometimes Delirium). - P. falciparum infection may show following clinical symptoms :
– This is the most dangerous of the malarias and patients are either ‘killed or cured’.
– The onset is often insidious, with malaise, headache and vomiting. Cough & mild diarrhoea are also common.
– The fever has no particular pattern.
– Jaundice is common due to haemolysis and hepatic dysfunction.
– Splenomegaly & hepatomegaly and may become tender.
– Anaemia develops rapidly, as does thrombocytopenia.
– A patient with falciparum malaria, apparently not seriously ill, may rapidly develop dangerous complications.
– Fatal falciparum malaria often involves the brain, a complication known as Cerebral malaria .
– Cerebral malaria is rapidly progressive & manifested by confusion, seizures or coma, & death usually occur within days to weeks.
– Children die rapidly without any special symptoms other than fever.
– Immunity is impaired in pregnancy & parasite can bind to a placental protein-chondroitin sulphate A.
– Abortion & intrauterine growth retardation from parasitisation of the maternal side of placenta are frequent.
– Fortunately, falciparum malaria usually pursues a chronic course, which may be punctuated at any time by blackwater fever.
– Previous splenectomy increases the risk of severe malaria.
Diagnosis :
Malarial parasite can be detected by following methods :
1. Peripheral blood film method / M.P. Slide method
- Giemsa-stained thick and thin blood films should be examined whenever malaria is suspected.
- Thick film examination is followed by thin film examination for confirmation.
2. Immunochromatographic tests
- OptiMal ®
- ParasightF ®
3. QBC Malaria Test
4. PCR technologie
Treatment :
- Malaria can be treated by following Anti-Malarial Drugs :
[wpsm_comparison_table id=”5″ class=””] - Systemic malarial treatment is given in following ways :
P. falciparum malaria treatment-
1. Mild P. falciparum malaria treatment :- Mild P. falciparum malaria is treated by following drugs :
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2. Severe & Complicated P. falciparum malaria treatment :- Severe & complicated P. falciparum Malaria should be treated immediately by following drugs :
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Patients should be monitored by ECG, with special attention to QRS duration and QT interval.
Non – P. falciparum malaria treatment-
P. vivax, P. ovale and P. malariae infections should be treated with following drugs :
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Note :-
- P. falciparum is now resistant to chloroquine and sulfadoxine-pyrimethamine (Fansidar) almost worldwide .
- Doxycycline should not be used in pregnancy .
- Artemether should be avoided in early pregnancy.
- Mefloquine should not be used for severe malaria since no parenteral form is available.
Prevention :
- Simple measures to reduce the frequency of infected-mosquito bites in malarious areas are very important. These measures include :
– Avoidance of exposure to mosquitoes at their peak feeding times (usually dusk to dawn)
– Use of insect repellents containing high-percentage diethyltoluamide (DEET) (or, if DEET is unacceptable, 7% picaridin).
– Covering up extremities when out after dark.
– Use of suitable clothing
– Use of insecticide-treated bed nets ( ITNs )or other insecticide-impregnated materials.
– Widespread use of bed nets treated with residual pyrethroids ( permethrin-impregnated mosquito nets ) reduces the incidence of malaria in areas where vectors bite indoors at night. - Clinical attacks of malaria may be preventable with chemoprophylaxis using follwing drugs :-
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