Malaria - Big Menace to Human Health in Tropical and Sub-tropical Regions of the World
-Dr. Arvind Singh
Malaria is an infectious disease transmitted by the biting of female Anopheles mosquito. It is one of the oldest known diseases caused by a protozoan known as Plasmodium. Since Romans were of the opinion that malaria is caused by the bad air of the swamps and marshes hence they called it malaria (in Italian malaria means bad or foul air). The disease was discovered by a French army surgeon named Alphonse Laveran who found that the condition is caused due to certain members of a family of protozoans parasites that enter the red blood cells. Another British doctor Patric Manson made similar observations while working in China and he also found evidence that his parasite was carried by mosquitoes and people get infected.
Malaria is one of the major causes of mortality and morbidity worldwide, affecting nearly 40% of the world's population and accounting for about 3-5 million deaths and more than 500 million new cases annually. Wide spread resistance of the parasite to common and easily accessible drugs like chloroquine and insecticide resistance in the mosquito vector has made the malaria situation very alarming.
Mosquitoes in large parts of India have become resistant to DDT, BHC, malathion, and fenitrothion consequently the number of malaria cases is increasing and the government is forced to spend large sums of money to control mosquitoes.
Africa, Asia, South America, Central America, and Asia-Pacific are the regions of the world where malaria persists as a major health problem. The condition is worst in the continent of Africa. Thus malaria is a serious menace to human health especially in tropical and sub-tropical regions of the world.
Causes of spread of Malaria:
The tropical and sub-tropical world faces the greatest challenges from emerging, re-emerging and spread of malaria as a result of demographic changes, rapid urbanization, global travel, and other environmental changes.
Urbanization, industrialization, migration, the building of dams, construction of canals to boost agricultural production, coal mining projects, increased use of pesticides, the increased area under paddy cultivation, floods, ecological alterations, global warming, etc. are the chief causes of spread and outbreak of malaria.
Urbanization and industrialization pull the rural population for the job opportunities in the urban areas. These migrant people transmit malaria to urban areas. Furthermore, the migrant population lives in slums in urban areas as a result of which insanitary conditions are created which favor the development and spread of malaria. Studies on malaria in Kolkata city reveals a rising trend in incidence of malaria since 1970s which is basically due to urbanization, industrialization, and migration.
The development of the Indira Gandhi canal in Rajasthan has led to the spread of malaria in the state. The increased area under paddy cultivation in India has substantially contributed to the transmission and spread of the disease as the water logged paddy fields provide an ideal breeding ground for mosquitoes.
The natural calamity, the flood have also been a cause of the spread and outbreak of malaria in India.
The Sardar Sarovar Water Resources Development Project in Gujarat, Bagri Dam Project in Madhya Pradesh and Konkan Railway Project in the Konkan region had led to an increased incidence of malaria in these projects affected areas.
Rise in Earth's temperature due to global warming has favored the growth and development of mosquito population thus resulting in an increase in incidence of malaria.
Ecological alteration like deforestation in Wet tropical Africa has caused several fold spread and outbreak in the incidence of malaria.
What is Plasmodium?
Plasmodium is single-celled protozoan that causes malaria in human beings. The parasite was discovered by Sir Ronald Ross in 1898. There are five different species of Plasmodium causing malaria in human beings. These include Plasmodium vivax, Plasmodium falciparum, Plasmodium over, Plasmodium malariae and Plasmodium knowlesi. As far as India is concerned Plasmodium vivax and Plasmodium falciparum are the species causing malaria whereas Plasmodium malaria in rare. However, Plasmodium ovale and Plasmodium knowlesi has not been reported from India so far.
Malaria caused by Plasmodium vivax, Plasmodium falciparum and Plasmodium malaria are known as Tertian malaria, Cerebral malaria, and Quartarian malaria, respectively. Cerebral malaria is the most fatal form of malaria which affects the brain.
Symptoms of Malaria:
Malarial symptoms appear about 9-14 days after the mosquito bite, although this varies with different Plasmodium species. The usual symptoms are an intermittent fever with enlargement of spleen. The intermittent fever is characterized by chill and shivering accompanied by headache, nausea and body ache. The fever subsides with profuse sweating.
Extreme weakness and hemolytic anemia are the other symptoms of the disease.
Malaria can kill by infecting and destroying red blood cells (anemia) and by clogging the capillaries that carry blood to the brain and other vital organs.
Life cycle of Plasmodium:
The malarial parasite Plasmodium undergoes development both in human beings and in female Anopheles mosquito. The mosquito ingests human blood through a bite. This blood contains the gametocytes a stage in the life cycle of the malarial parasite. In the stomach of the mosquito, male gametocytes fertilize with female resulting into formation of a zygote. The zygote increase in size and becomes mobile; which pierces the stomach wall of the mosquito and a cyst is formed. Infective forms known as sporozoites appear in this cyst. In 7-20 days they reach the salivary glands and proboscis of the mosquito. When this infected mosquito bites human beings these sporozoites are introduced into human tissues. Sporozoites then enter the bloodstream and reach the liver. In the liver, the merozoites are released out of them, it is when merozoites, enter the blood, does the fever. This cycle is completed in 48 hours in case of Plasmodium vivax and Plasmodium falciparum and the same takes 72 hours in Plasmodium malariae.
Medicines prescribed for Malaria:
Chloroquine, quinine, and mepacrine are usually prescribed for the treatment of malaria. Since malarial parasites have developed resistance against chloroquine hence in such cases Sulphadoxine with Pyrimethamine is prescribed. Combinations of mefloquine, quinine with antibiotics tetracycline, doxycycline, chloroquine are also used.
While visiting a place where malaria is endemic as a precautionary measure drug prophylaxis must be started two weeks before and continued for at least 4-6 weeks after leaving the malaria-endemic area. Different doses of chloroquine, amodiaquine, sulphadoxine-pyrimethamine are prescribed.
Control of Malaria:
Since the malarial parasite is only transmitted by mosquitoes the control of malaria depends on preventing mosquitoes from biting humans and where possible the eradication of mosquitoes.
Female mosquitoes lay their eggs in stagnant water in ponds, lakes or ditches, or even in small amounts of rain-water lying in puddles, drinking trough or cans. The eggs soon hatch into larvae, which feed on the microscopic plants in the water. The larvae live at the surface of the water breathing air through a tracheal tube. Ultimately it pupates; the pupa, although it does not feed, still breathes air. Finally, the pupal skin splits open and the imago emerges and flies away.
Methods of mosquito eradication are directed at each of the stages of its development. The adult insect should be attacked with pesticide sprays that are not harmful to other life forms. The breeding grounds of the mosquito should be destroyed by draining ponds, stagnant swamps, turning sluggish rivers into swiftly flowing steam, and by preventing the accumulation of water in puddles or tanks accessible to the mosquito. Marshy places should be covered with sand. Vegetation, the usual shelter for the mosquitoes around the streams should be destroyed.
Treating static water with oil-based sprays produces a film of oil on the water which suffocates the larvae and pupae by blocking their breathing tubes; the addition of pesticides to the sprays increases their effectiveness. Such spraying must include not only lakes and ponds but any accumulation of water which mosquitoes can reach, such as drains and gutters and even the small amounts collected in the old tin cans and other rubbish.
What is Sickle cell anemia?
In several regions of the African continent where malaria is endemic, sickle cell anemia in the heterozygous state is a cultural adaptation to cope up with the problem of malaria. Sickle cell anemia is a genetic disorder in which abnormal haemoglobin is produced as a result of which red blood cells become sickle-shaped and ultimately collapses. Consequently, the malarial parasite parasitizing the red blood cells also die. The disease is caused by a recessive gene. Homozygous individuals normally die early in life due to severe anemia caused by the destruction of the sickled red cells. However, heterozygous individuals who have both normal and abnormal haemoglobin and who also have mild anaemia, are naturally protected against contracting malaria as the parasite cannot survive in these distorted cells.
What is the source of Artemisinin?
Artemisia annua (a herbaceous plant belonging to Asteraceae family of flowering plants) is source of drug artemisinin which is used in the treatment of cerebral malaria. The plant is native of China.
How Malaria is diagnosed?
Malaria is diagnosed by a blood test. The MP / MF tests are conducted to detect the malarial parasite in the blood, MP test stands of malaria plain while the MF stands for malaria Falciparum.
What is the source of Quinine?
Cinchona calysia (a tree belonging to Rubiaceae family of flowering plant) is a source of drug quinine which has been used in the treatment of malaria for the last 400 years. The drug is obtained from the bark of the tree. Cinchona calysia is native of South America where its bark has traditionally been used as antipyretics.
What are the side effects of anti-malarial drugs?
Chloroquine can cause nausea, vomiting and itching while Amodiaquine can cause serious blood disorders but rarely. Quinine can cause tinnitus, deafness or dizziness whereas Primaquine can cause abdominal pain.
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Dr. Arvind Singh is M. Sc. and Ph. D. in Botany with an area of specialization in Ecology. He is a dedicated Researcher having more than four dozen published Research Papers in the Journals of National and International repute. His main area of Research is Restoration of Mined Lands. However, he has also conducted research on the Vascular Flora of Banaras Hindu University-Main Campus, India.
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