This book discussed about Plasmodium vivax is a protozoal parasite and a human pathogen. The most frequent and widely distributed cause of recurring (Benign tertian) malaria, P. vivax is one of the six species of malaria parasites that commonly infect humans. It is less virulent than Plasmodium falciparum, the deadliest of the six, but vivax malaria can lead to severe disease and death due to splenomegaly (a pathologically enlarged spleen). It afflicted as many as eight U.S. presidents¿including George Washington and Abraham Lincoln¿and may have helped kill Genghis Khan. P. vivax is carried by the female Anopheles mosquito, since it is only the female of the species that bite. P. vivax was found mainly in the United States, Latin America, and in some parts of Africa. More recently it became a plague of low- and middle-income countries, except those in sub-Saharan Africa, where the P. vivax map has a conspicuous hole. Overall it accounts for 65% of malaria cases in Asia and South America. As overall malaria rates fall in a region, its proportion of cases increases. It has been estimated that 2.5 billion people are at risk of infection with this organism.