Schellackia

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. The parasites deform erythrocytes of the host into crescents, and can be visualised 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. In more recent years, however, molecular characterisation methods have allowed more precise determination of species identity and their phylogenetic relationship. As is typical of Apicomplexans, Schellackia replicates via multiple fission. The parasite utilises both merogony (asexual) and gametogony (sexual), with both processes occurring within the mucosal epithelium of the duodenum of infected hosts. 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. Gametogony occurs later in an 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.