Schellackia
From Wikipedia, the free encyclopedia
| Schellackia | |
|---|---|
Scientific classification  | |
| Domain: | Eukaryota |
| Clade: | Sar |
| Superphylum: | Alveolata |
| Phylum: | Apicomplexa |
| Class: | Conoidasida |
| Order: | Eucoccidiorida |
| Family: | Lankesterellidae |
| Genus: | Schellackia Reichenow, 1920 |
| Species | |
|
Schellackia balli [1] | |
The genus Schellackia comprises obligate unicellular eukaryotic parasites within the phylum Apicomplexa, and infects numerous species of lizards and amphibians worldwide. Schellackia is transmitted via insect vectors, primarily mites and mosquitoes, which take up the parasite in blood meals. These vectors then subsequently infect reptilian and amphibian which consume the infected insects.[5] The parasites deform erythrocytes of the host into crescents, and can be visualized using a blood smear.
The type species, Schellackia bolivari, was described by Anton Reichenow in 1919.
Schellackia was first described by Anton Reichenow in 1919, with the type species Schellackia bolivari having been discovered parasitizing the spiny-footed lizard Acanthodactylus erythrurus and the Spanish Psammodromus hispanicus within the Iberian Peninsula.
At first, many difficulties in describing new species were present – very few characteristics could be described from blood sporozoites within the primary host, with most defining characteristics being restricted to the parasite’s endogenous stages within the gut epithelium of the host. This led to relatively few described species for a parasite genus that was supposedly very geographically widespread.[6]
In more recent years, however, molecular characterization methods have allowed a more precise determination of species identity and their phylogenetic relationship.[6]
Life cycle
As is typical of Apicomplexans, Schellackia replicates via multiple fission. The parasite utilizes both merogony (asexual) and gametogony (sexual), with both processes occurring within the mucosal epithelium of the duodenum of infected hosts.[7]
Young meronts can be expected to be around 6 μm in diameter, growing up to around 30 μm as they mature before they divide into merozoites. However, these figures and the time required for maturation can vary between species. The meronts subsequently split via cytokinesis, dividing into usually around 8 to 32 merozoites which are released as the host cell ruptures. Post-merogony, the development of merozoites produces a residual body of variable size. Merozoites are non-motile and proceed to infect other cells in order to rapidly reproduce.[7]
Gametogony occurs later in infection, generally after the majority of merogony activity. Male gametocytes (microgamonts) divide to form flagellated microgametes, while female gametocytes (macrogamonts) concurrently differentiate into macrogametes, sometimes even within the same host cell. These gametes then fuse forming zygotes within the epithelial layer of the duodenum of the host.[7]
Subsequently, zygotes transition to an oocyst stage. This transition is marked by the formation of large refractile bodies within the oocysts, soon followed by the appearance of developing sporozoites. The mature octonucleate oocyst is a characteristic phase of Schellackia’s lifecycle. Eventually, the oocyst divides by endopolygeny into eight sporozoites which combine with extensions of the refractory body as they exit the ruptured oocyst. This process leaves behind empty spaces within the epithelium and lamina propria of the host.[7]
The sporozoites then make their way into the host’s blood cells including erythrocytes, leucocytes and macrophages. The sporozoites often exist within a common parasitophorous vacuole which is shared with other sporozoites, although some also dwell within their own individual vacuole.[7]
The presence of sporozoites within the blood cells of the host allows the parasite to proliferate to additional hosts via blood-consuming insect vectors such as mites, ticks and mosquitos.[5]
