''Karyolysus'' is a genus of coccidia.
With the exception of ''K. sonomae'' whose vertebrate host is the yellow-legged frog (''
Rana boylii boylii''), species in this genus only infect lizards of the genus ''
Lacerta
Lacerta is one of the 88 modern constellations defined by the International Astronomical Union. Its name is Latin for lizard. A small, faint constellation, it was defined in 1687 by the astronomer Johannes Hevelius. Its brightest stars form a "W" ...
''.
History
The genus was created by Labbe in 1894 for those species of sporozoans that fragmented the host nucleus. Reichenow in 1921 established that this property was of dubious taxonomic value. He proposed a different set of criteria for inclusion in this genus and these are the one currently in use.
The type species is ''Karyolysus lacertae''
.
Characteristics of the genus
Schizogeny occurs in the
endothelial cell
The endothelium (: endothelia) 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 th ...
s
Gametogony
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 organis ...
occurs in the
erythrocyte
Red blood cells (RBCs), referred to as erythrocytes (, with -''cyte'' translated as 'cell' in modern usage) in academia and medical publishing, also known as red cells, erythroid cells, and rarely haematids, are the most common type of blood ce ...
s after their penetration by the
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 i ...
s.
Differentiation from the genus ''
Haemogregarina'' may be difficult as in both genera gametocytogenesis occurs in the erythrocytes and have similar morphology. They can be distinguished on the location of schizogony: In ''Karyolysus'' this occurs in the endothelial cells of the visera while in ''Haemogregarina'' schizogony occurs in the
bone marrow
Bone marrow is a semi-solid biological tissue, tissue found within the Spongy bone, spongy (also known as cancellous) portions of bones. In birds and mammals, bone marrow is the primary site of new blood cell production (or haematopoiesis). It i ...
.
Life cycle
Starting with infected
mite
Mites are small arachnids (eight-legged arthropods) of two large orders, the Acariformes and the Parasitiformes, which were historically grouped together in the subclass Acari. However, most recent genetic analyses do not recover the two as eac ...
s which the host
lizard
Lizard is the common name used for all Squamata, squamate reptiles other than snakes (and to a lesser extent amphisbaenians), encompassing over 7,000 species, ranging across all continents except Antarctica, as well as most Island#Oceanic isla ...
ingests the veriform
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 organis ...
s are released from the
sporocysts. These newly liberated sporozoites bore into the intestinal wall and enter the
lymph
Lymph () is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues to be recirculated. At the ori ...
atic vessels and the
blood
Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells.
Blood is com ...
stream. On reaching the viscera and in particular the
liver
The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...
the sporozoites penetrate the endothelial cells. There they form ovoid schizonts within a membranous capsule. They remain in these cells for some time and give rise to 8 to 30 merozoites. The merozoites remain in the cell for some time before rupturing it and entering the blood stream.
On entering the blood stream the merozoites penetrate other endothelial cells. There they grow and undergo schizogeny producing a number of small merozoites. These second generation schizonts are smaller than the first generation and lack a discernable
nucleus
Nucleus (: nuclei) is a Latin word for the seed inside a fruit. It most often refers to:
*Atomic nucleus, the very dense central region of an atom
*Cell nucleus, a central organelle of a eukaryotic cell, containing most of the cell's DNA
Nucleu ...
. These are also eventually released into the blood stream, this occurs usually day 42 post infection.
These small merozoites are actually
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
T ...
s. These penetrate erythrocytes and differentiate into
macrogametoctyes and
microgametocytes. Both types are surrounded by a thin membrane. The microgametocytes remain thin and do not develop a nucleus. The macrogametocytes in contrast enlarge and develop a visible nucleus at one end of the nucleus.
On ingestion by a female mite (male mites do not require blood) the gametocytes are released from the erythrocytes. Within the gut they associate in spindle like pairs and enter the epithelial cells of the gut. Within the epithelial cell the macrogametocyte increases in size while the microgametocyte shrinks. The microgametocyte divides in two and one of the motile gametes so formed fuses with the macrogametocyte to form a
zygote
A zygote (; , ) is a eukaryote, eukaryotic cell (biology), cell formed by a fertilization event between two gametes.
The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individ ...
.
The zygote (or
ookinete) grows within the cell and undergoes
meiosis
Meiosis () is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, the sperm or egg cells. It involves two rounds of division that ultimately result in four cells, each with only one c ...
followed by several rounds of
mitosis
Mitosis () is a part of the cell cycle in eukaryote, eukaryotic cells in which replicated chromosomes are separated into two new Cell nucleus, nuclei. Cell division by mitosis is an equational division which gives rise to genetically identic ...
. The ookinte is now known as an oocyst. Within the oocyst the nuclei migrate to the surface of the oocyst and gather cytoplasm around them becoming known as