More than half of the world's population is at risk of malaria. These include such places as sub-Saharan Africa,as well as Asia, Latin America and even the Middle East and some areas in Europe. There are four different parasite species called Plasmodium--P. falciparum, P. vivax, P. malariae, and P. ovale. The most deadly is P. falciparum which causes thousands of deaths per year due to malaria. An Anopholes mosquito carries the parasite. When it bites a human, the parasite multiplies in the liver and within two weeks or less, symptoms appear. The parasite destroys red blood cells. This can lead to death by anemia and a clogging of the tiniest blood vessels called capillaries. Symptoms include fever, chills, headache and flu-like symptoms. In some areas of the world, the mosquitoes have become resistant to the insecticides used to kill the mosquitoes and to the medicine used to treat malaria. Scientists are working on a vaccine to treat this scourge.