Plasmodium falciparum

Plasmodium falciparum is a unicellular protozoan parasite of humans, and the deadliest species of Plasmodium that cause malaria in humans. It is transmitted through the bite of a female Anopheles mosquito. It is responsible for roughly 50% of all malaria cases. It causes the disease's most dangerous form called falciparum malaria. It is therefore regarded as the deadliest parasite in humans, causing 435,000 deaths in 2017. It is also associated with the development of blood cancer (Burkitt's lymphoma) and is classified as Group 2A carcinogen. The species originated from the malarial parasite Laverania found in gorillas, around 10,000 years ago. Alphonse Laveran was the first to identify the parasite in 1880, and named it Oscillaria malariae. Ronald Ross discovered its transmission by mosquito in 1897. Giovanni Battista Grassi elucidated the complete transmission from a female anopheline mosquito to humans in 1898. In 1897, William H. Welch created the name Plasmodium falciparum, which ICZN formally adopted in 1954. P. falciparum assumes several different forms during its life cycle. The human-infective stage are sporozoites from the salivary gland of a mosquito. The sporozoites grow and multiply in the liver to become merozoites. These merozoites invade the erythrocytes (RBCs) to form trophozoites, schizonts and gametocytes, during which the symptoms of malaria are produced. In the mosquito, the gametocytes undergo sexual reproduction to a zygote, which turns into ookinete. Ookinete forms oocyts from which sporozoites are formed. As of the latest World Malaria Report of the World Health Organization, there were 219 million cases of malaria worldwide in 2017, up from 216 million cases in 2016. This resulted in an estimated 435,000 deaths. Almost every malarial death is caused by P. falciparum, and 93% of death occurs in Africa. Children under five years of age are most affected, accounting for 61% of the total deaths. In Sub-Saharan Africa, over 75% of cases were due to P. falciparum, whereas in most other malarial countries, other, less virulent plasmodial species predominate. Falciparum malaria was familiar to the ancient Greeks, who gave the general name πυρετός pyretós 'fever'. Hippocrates (c. 460-370 BCE) gave several descriptions on tertian fever and quartan fever. It was prevalent throughout the ancient Egyptian and Roman civilizations. It was the Romans who named the disease 'malaria'—mala for bad, and aria for air, as they believed that the disease was spread by contaminated air, or miasma. A German physician, Johann Friedrich Meckel, must have been the first to see P. falciparum but without knowing what it was. In 1847 he reported the presence of black pigment granules from the blood and spleen of a patient who died of malaria. The French Army physician Charles Louis Alphonse Laveran, while working at Bône Hospital (now Annaba in Algeria), correctly identified the parasite as a causative pathogen of malaria in 1880. He presented his discovery before the French Academy of Medicine in Paris, and published it in The Lancet, in 1881. He gave the scientific name Oscillaria malariae. But his discovery was received with skepticism mainly because by that time leading physicians such as Theodor Albrecht Edwin Klebs and Corrado Tommasi-Crudeli claimed that they had discovered a bacterium (which they called Bacillus malariae) as the pathogen of malaria. Laveran's discovery was widely accepted only after five years when Camillo Golgi confirmed the parasite using better microscope and staining technique. Laveran was awarded the Nobel Prize in Physiology or Medicine in 1907 for his work. In 1900, the Italian zoologist Giovanni Battista Grassi categorized Plasmodium species based on the timing of fever in the patient; malignant tertian malaria was caused by Laverania malariae (now P. falciparum), benign tertian malaria by Haemamoeba vivax (now P. vivax), and quartan malaria by Haemamoeba malariae (now P. malariae). The British physician Patrick Manson formulated the mosquito-malaria theory in 1894; until that time, malarial parasites were believed to be spread in air as miasma, a Greek word for pollution. His colleague Ronald Ross, a British Army surgeon, travelled to India to test the theory. Ross discovered in 1897 that malarial parasites lived in certain mosquitoes. The next year, he demonstrated that a malarial parasite of birds could be transmitted by mosquitoes from one bird to another. Around the same time, Grassi demonstrated that P. falciparum was transmitted in humans only by female anopheline mosquito (in his case Anopheles claviger). Ross, Manson and Grassi were nominated for the Nobel Prize in Physiology or Medicine in 1902. Under controversial circumstances, only Ronald Ross was selected for the award. There was a long debate on the taxonomy. It was only in 1954 the International Commission on Zoological Nomenclature officially approved the binominal Plasmodium falciparum. The valid genus Plasmodium was created by two Italian physicians Ettore Marchiafava and Angelo Celli in 1885. The species name was introduced by an American physician William Henry Welch in 1897. It is derived from the Latin falx, meaning 'sickle' and parum meaning 'like or equal to another'. P. falciparum is now generally accepted to have evolved from Laverania (a subgenus of Plasmodium found in apes) species present in gorilla in Western Africa. Genetic diversity indicates that the human protozoan emerged around 10,000 years ago. The closest relative of P. falciparum is P. praefalciparum, a parasite of gorillas, as supported by mitochondrial, apicoplastic and nuclear DNA sequences. These two species are closely related to the chimpanzee parasite P. reichenowi, which was previously thought to be the closest relative of P. falciparum. P. falciparum was also once thought to originate from a parasite of birds.