MALARIA: A DEADLY DISEASE

• Malaria is a potentially deadly tropical disease characterized by cyclical bouts of fever with muscle stiffness, shaking and sweating. It is caused by a tiny parasite (genus Plasmodium) that is transmitted by the female mosquito (genus Anopheles) when it feeds on blood for its developing eggs.
• Severe malaria is not readily distinguishable from other severe diseases, such as pneumonia typhoid and meningitis that require very different therapy.
• Almost all vertebrates, birds, snakes and monkeys, for example, can be infected by Plasmodium (malaria) parasites. Different animal species can only be infected by their own specific species of Plasmodium.
• Humans are generally host to four species of malaria parasites: Plasmodium falciparum, Plasmodium vivax, Plasmodium ovale, and Plasmodium malariae. Plasmodium falciparum causes the most dangerous complications, such as cerebral malaria. It is the species that is most virulent and potentially lethal to humans.
• Because of its dependence on human/vector (mosquito) contact, malaria is considered to be a disease of poverty. Poor people can be physically marginalized and live closer to degraded land and conditions where mosquitoes thrive. They are also less likely to have physical barriers such as screens or nets to protect them and they often lack the education and resources to access proper care and treatment.
• Intense and costly control programmes targeting malaria, that incorporate a variety of approaches such as environmental modification and indoor spraying with DDT, have succeeded in eliminating or significantly reducing the disease in many countries. Malaria has been eliminated in former Soviet Republics, the USA, Italy, Korea and many Caribbean Islands.
• The Anopheles gambiae mosquito selects small, sunlit collections of water to lay its eggs. The intact forest provides few such breeding sites so there are few malarious mosquitoes in dark jungles and tropical forests. Replacing tropical forests with agricultural land provides the mosquitoes with the conditions and proximity to human hosts that they require to thrive.
• Malaria is transmitted by an infected, female mosquito; Anopheles gambiae. It can also be acquired from an infected blood transfusion or even from the shared needles of drug addicts.
• Human malaria parasites only develop in Anopheles mosquitoes. The parasites move to the salivary glands of the mosquito and are injected into a human host by the feeding insect.

• The anopheline mosquito only feeds in the evening. The parasite is injected into the host when the mosquito feeds and then progresses through a number of stages and transformations. The threadlike malaria parasites enter the bloodstream and are carried to the liver where they invade liver tissue cells, transform into spores and replicate repeatedly.
• The spores, formed within cyst-like structures in the liver, are released into the bloodstream where they attack and destroy red blood cells. In the process, they undergo another transformation that allows a form of the parasite to attack and invade new red blood cells.
• The synchronized development of different stages of the parasite is responsible for the characteristic cycles of fever in infected humans. A form of the parasite periodically bursts from demolished cells and is released into the blood stream to invade new blood cells. Different species produce different fever cycles.
• Plasmodium falciparum has a forty-eight hour period between fever peaks. The process is repeated over and over until natural or acquired immunity, or antimalarial chemotherapy, or death brings the repetitive process to an end.
• When an anopheline mosquito takes blood from a malarious human, the parasite enters the mosquito and goes through a number of complex changes over a 14 to 21 day period. It becomes an infectious form and moves to the mosquito's salivary glands where it is ready to reinfect and complete the cycle.
• Many people in Africa and other areas with intense malaria transmission, carry parasites without being ill. Having been infected repeatedly, they have built up immunity to the disease.
• The malaria situation around the world is worsening. Social and environmental factors are bringing more humans into closer contact with the mosquito carrier. The widespread use of chloroquine has allowed the emergence of resistant strains of Plasmodium falciparum that no longer respond to the drug. Plasmodium falciparum has become resistant to the most common antimalarial drugs in most of its area of distribution. Mosquitoes are also becoming more resistant to chemical insecticides.
• Changes in the immune system make women particularly vulnerable to life threatening infections from malaria during pregnancy. In addition to the acute effects, malaria causes anaemia in children and pregnant women and increases their vulnerability to other diseases. Repeated bouts of malarial fever in young children reduces their immunity and interferes with feeding, thus increasing their vulnerability to other diseases and death.

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