genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of parasitic
alveolates
The alveolates (meaning "pitted like a honeycomb") are a group of protists, considered a major clade and superphylum within Eukarya. They are currently grouped with the stramenopiles and Rhizaria among the protists with tubulocristate mitochondr ...
belonging to the phylum
Apicomplexa
The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic alveolates. Most of them possess a unique form of organelle that comprises a type of non-photosynthetic plastid called an apicoplast, and an apical complex structure. T ...
(which also includes the malaria parasites).
The species of this genus use either blackflies (''
Simulium
''Simulium'' is a genus of black flies, which may transmit diseases such as onchocerciasis (river blindness). It is a large genus with several hundred species, and 41 subgenera.
The flies are pool feeders. Their saliva, which contains antico ...
'' species) or a
biting midge
Ceratopogonidae is a family of flies commonly known as no-see-ums, or biting midges, generally in length. The family includes more than 5,000 species, distributed worldwide, apart from the Antarctic and the Arctic.
Ceratopogonidae are holom ...
as their definitive host and
birds
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
as their intermediate host. There are over 100 species in this genus. Over 100 species of birds have been recorded as hosts to these parasites.
Life cycle
Parasites in the genus ''Leucocytozoon'' have a life cycle that involves both a bird host, and a
black fly
A black fly or blackfly (sometimes called a buffalo gnat, turkey gnat, or white socks) is any member of the family Simuliidae of the Culicomorpha infraorder. It is related to the Ceratopogonidae, Chironomidae, and Thaumaleidae. Over 2,200 speci ...
(with the exception of ''Leucocytozoon caulleryi'' which cycles between a bird host and a
biting midge
Ceratopogonidae is a family of flies commonly known as no-see-ums, or biting midges, generally in length. The family includes more than 5,000 species, distributed worldwide, apart from the Antarctic and the Arctic.
Ceratopogonidae are holom ...
). Parasites enter the bird host in a form called a
sporozoite
Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism i ...
through the bite of the blood-sucking black fly. The sporozoites invade host cells in the liver where they undergo asexual replication, forming numerous daughter cells called
merozoite
Apicomplexans, a group of intracellular parasites, have life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an apicomplexan organism is ...
s within 4–5 days. The duration of this stage depends in part upon the species. In some species this stage may occur in the endothelial cells instead of the liver.
The newly released merozoites infect either
erythrocyte
Red blood cells (RBCs), also referred to as red cells, red blood corpuscles (in humans or other animals not having nucleus in red blood cells), haematids, erythroid cells or erythrocytes (from Greek ''erythros'' for "red" and ''kytos'' for "holl ...
s,
leukocyte
White blood cells, also called leukocytes or leucocytes, are the cells of the immune system that are involved in protecting the body against both infectious disease and foreign invaders. All white blood cells are produced and derived from mult ...
s,
macrophage
Macrophages (abbreviated as M φ, MΦ or MP) ( el, large eaters, from Greek ''μακρός'' (') = large, ''φαγεῖν'' (') = to eat) are a type of white blood cell of the immune system that engulfs and digests pathogens, such as cancer cel ...
s or
endothelial cell
The endothelium is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel ...
s. Those infecting the macrophages or endothelial cells develop into megaloschizonts. The megaloschizonts divide into primary cytomeres, which in turn multiply into smaller cytomeres, which mature into schizonts, which in turn divide into merozoites. In erythrocytes or leukocytes, merozoites develop into
gametocyte
A gametocyte is a eukaryotic germ cell that divides by mitosis into other gametocytes or by meiosis into gametids during gametogenesis. Male gametocytes are called ''spermatocytes'', and female gametocytes are called ''oocytes''.
Development
...
s.
The gametocytes are taken up by a blood-sucking fly as it bites the bird host. Gametocytes then mature in the insect
midgut
The midgut is the portion of the embryo from which most of the intestines develop. After it bends around the superior mesenteric artery, it is called the "midgut loop". It comprises the portion of the alimentary canal from the end of the foregut ...
into macrogametocytes (female) with red-staining nuclei and microgametocytes (male) with pale-staining diffuse nuclei: these fuse to form an
ookinete
Apicomplexans, a group of intracellular parasites, have Biological life cycle, life cycle stages that allow them to survive the wide variety of environments they are exposed to during their complex life cycle. Each stage in the life cycle of an a ...
. The male gametocytes normally give rise to eight