Plasmodium is a genus of parasites of vertebrates and insects. Species of Plasmodium are distributed globally wherever suitable hosts are found. They are the causative agent of malaria.
Insect hosts are most frequently mosquitoes. Vertebrate hosts include reptiles, birds, and mammals. Humans develop malaria when infacted.
The five species that regularly infect humans are: P. vivax, P. falciparum, P. malariae, P. ovale, and P. knowlesi.
P. falciparum is by far the most lethal in humans, resulting in hundreds of thousands of deaths per year.