Editing Plasmodium (section)

==Life cycle==
[[File:Life Cycle of the Malaria Parasite.jpg|thumb|right|Life cycle of a species that infects humans]]
[[File:Malarial parasites, Plasmodium species, ring forms in red blood cells.jpg|right|thumb|Ring forms of ''Plasmodium'' inside human red blood cells ([[Giemsa stain]])]]

The life cycle of ''Plasmodium'' involves several distinct stages in the insect and vertebrate [[Host (biology)|hosts]]. Parasites are generally introduced into a vertebrate host by the bite of an insect host (generally a mosquito, with the exception of some ''Plasmodium'' species of reptiles).<ref name=Sullivan>{{cite book|title=Malaria: Drugs, Disease, and Post-genomic Biology |date=2005 |editor1=Sullivan, D |editor2=Krishna, S.  |publisher=Springer |isbn=978-3-540-29088-9 |chapter=Molecular Genetics of Mosquito Resistance to Malaria Parasites |author1=Vernick, K.D. |author2=Oduol, F. |author3=Lazarro, B.P. |author4=Glazebrook, J. |author5=Xu, J. |author6=Riehle, M. |author7=Li, J. |page=384}}</ref> Parasites first infect the liver or other tissue, where they undergo a single large round of replication before exiting the host cell to infect [[red blood cell|erythrocytes]].<ref name=CDCBiology>{{cite web |title=CDC – Malaria Parasites – Biology|url=https://www.cdc.gov/malaria/about/biology/index.html |website=CDC: Malaria |publisher=U.S. Centers for Disease Control and Prevention |access-date=28 December 2015}}</ref> At this point, some species of ''Plasmodium'' of primates can form a long-lived dormant stage called a hypnozoite,<ref>{{cite journal | author=Markus, M. B. | title = Malaria: Origin of the Term 'Hypnozoite' | journal = Journal of the History of Biology | volume = 44 | issue = 4 | pages = 781–786 | date = 2011 | pmid = 20665090 | doi = 10.1007/s10739-010-9239-3| s2cid = 1727294 }}</ref> which can remain in the liver for more than a year.<ref>{{cite journal|doi=10.1101/cshperspect.a025486 |pmid=28242785 |title=Malaria Parasite Liver Infection and Exoerythrocytic Biology |journal=Cold Spring Harbor Perspectives in Medicine |volume=7 |issue=6 |pages=a025486 |year=2017 |last1=Vaughan |first1=Ashley M. |last2=Kappe |first2=Stefan H. I. |pmc=5453383 }}</ref> However, for most ''Plasmodium'' species, the parasites in infected liver cells are only what are called merozoites. After emerging from the liver, they enter red blood cells, as explained above. They then go through continuous cycles of erythrocyte infection, while a small percentage of parasites differentiate into a sexual stage called a gametocyte which is picked up by an insect host taking a blood meal. In some hosts, invasion of erythrocytes by ''Plasmodium'' species can result in disease, called malaria. This can sometimes be severe, rapidly followed by death of the host (e.g. ''P. falciparum'' in humans). In other hosts, ''Plasmodium'' infection can apparently be asymptomatic.<ref name=Sullivan/>

Even when humans have such subclinical plasmodial infections, there can nevertheless be very large numbers of multiplying parasites concealed in, particularly, the spleen and bone marrow. Certainly, this applies in the case of ''P. vivax''. These hidden parasites (in addition to hypnozoites) are thought to be the origin of instances of recurrent ''P. vivax'' malaria.<ref>{{cite journal |last1=Markus |first1=M. B. |title=Theoretical origin of genetically homologous Plasmodium vivax malarial recurrences |journal=Southern African Journal of Infectious Diseases |date=2022 |volume=37 |issue=1 |page=369 |doi=10.4102/sajid.v37i1.369 |pmid=35399558 |pmc=8991251}}</ref>

[[File:Malaria Sporozoites (16657642929).jpg|thumb|upright|[[Sporozoite]]s, one of several different forms of the parasite, from a mosquito]]

Within the red blood cells, the merozoites grow first to a ring-shaped form and then to a larger form called a [[trophozoite]]. Trophozoites then mature to [[schizont]]s which divide several times to produce new merozoites. The infected red blood cell eventually bursts, allowing the new merozoites to travel within the bloodstream to infect new red blood cells. Most merozoites continue this replicative cycle, however some merozoites upon infecting red blood cells differentiate into male or female sexual forms called gametocytes. These gametocytes circulate in the blood until they are taken up when a mosquito feeds on the infected vertebrate host, taking up blood which includes the gametocytes.<ref name=CDCBiology/>

In the mosquito, the gametocytes move along with the [[hematophagy|blood meal]] to the mosquito's midgut. Here the [[gametocyte]]s develop into male and female [[gamete]]s which [[fertilization|fertilize]] each other, forming a [[zygote]]. Zygotes then develop into a motile form called an [[ookinete]], which penetrates the wall of the midgut. Upon traversing the midgut wall, the ookinete embeds into the gut's exterior membrane and develops into an oocyst. Oocysts divide many times to produce large numbers of small elongated [[sporozoite]]s. These sporozoites migrate to the salivary glands of the mosquito where they can be injected into the blood of the next host the mosquito bites, repeating the cycle.<ref name=CDCBiology/>