LONDON, England -- Malaria is one of the world's worst health problems and one of its biggest killers, with half a billion people affected every year, according to the Roll Back Malaria partnership.



Around half a billion people are infected with malaria every year. Ninety percent of those cases are in Africa.



Saturday marks World Malaria Day, when the world commemorates global efforts to eradicate the disease.



Below CNN's Vital Signs has produced a complete A - Z guide to how malaria spreads, the symptoms to look out for and how to protect yourself.



A is for Anti-malarial drugs The history of anti-malarial medicine has been marked by a constant struggle between evolving drug-resistant parasites and the search for new drugs. Currently, anti-malaria experts are focusing on therapies that combine several drugs for better effects.



B is for Blood stream Once a mosquito has bitten and the malaria parasites reach the liver, the parasites divide and create thousands of mature parasites. These are released into the blood and infect red blood cells.  At that point, typical malaria symptoms such as fever and anemia develop.



C is for Chloroquine Until recently, Chloroquine, an anti-malarial drug, was the first option for many people because of its relatively low price and effectiveness. However, resistance to Chloroquine in many parts of the world has rendered the drug ineffective.



D is for Diagnosis After noting your symptoms and travel history, your doctor will likely obtain a sample of your blood for observation. Two blood samples, taken at six- and 12-hour intervals, can usually confirm the presence of the malaria parasite and its type. It is possible to be infected by more than one parasite at the same time.



E is for Epidemic According to the World Health Organization (WHO), large and devastating epidemics can occur when the mosquito-borne parasite is introduced into areas where people have had little prior contact with the infecting parasite. These epidemics can be triggered by wet weather conditions and further aggravated by floods or mass population movements driven by conflict.



F is for Fever The most common symptom of all types of malarias is high fever, which is why doctors often misdiagnose malaria for flu. The fever is a reaction to toxins in the blood. It is therefore advised to tell your doctor you have been to a malaria affected zone, even if symptoms arise months after the trip.



G is for Genome  In 2002, -- hundred years after it was discovered that mosquitoes transmit the malaria parasite -- the complete genetic codes of both the human malaria parasite and the mosquito that spreads it was cracked. This development brought scientists a step closer to developing drugs and vaccines to fight the disease, Nature magazine reported.



H is for Hotspots Most cases and deaths are in sub-Saharan Africa, many of them occurring among children. However, Asia, Latin America, the Middle East and parts of Europe are also affected. In 2006, malaria was present in 109 countries and territories.



I is for Immunity Travelers from malaria-free regions such as Europe and the United States, with little or no immunity, who go to areas with high disease rates, are particularly vulnerable. It is essential to take precautions by taking anti-malarial drugs prescribed by your doctor.



J is for Julius Wagner-Jauregg Julius Wagner-Jauregg, a Viennese doctor, was the first to intentionally infect syphilis patients with malaria parasites. By controlling the subsequent malaria-related fever with an anti-malaria drug, the effects of both syphilis and malaria could be minimized. Jauregg received the Nobel Prize in Medicine in 1927.



K is for Killer Malaria is a life-threatening disease but it is preventable and curable if the right steps are taken. Education in recognizing the symptoms has reduced the number of cases in some areas by 20 percent. Recognizing the disease in the early stages can stop the disease from becoming a killer.



L is for Laser gun U.S. scientists say they are developing a laser gun that could kill millions of mosquitoes in minutes. The laser fires at mosquitoes once it detects the audio frequency created by the beating of wings,
What is the date of World Malaria Day? How many cases of malaria were there in 2006? What does "WHO" stand for? When is World Malaria Day? how many cases of malaria
Saturday was present in 109 countries and territories. World Health Organization Saturday half a billion people affected every year,
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