Schellackia

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Schellackia
Scientific classification
Domain:
Eukaryota
(unranked):
Sar
(unranked):
Alveolata
Phylum:
Apicomplexa
Class:
Conoidasida
Subclass:
Coccidiasina
Order:
Eucoccidiorida
Suborder:
Eimeriorina
Family:
Lankesterellidae
Genus:
Schellackia
Species

Schellackia balli [1]
Schellackia bolivari
Schellackia brugooi
Schellackia calotesi [2]
Schellackia cf agamae
Schellackia golvani
Schellackia iguanae
Schellackia landauae [3]
Schellackia legeri
Schellackia occidentalis [4]
Schellackia orientalis
Schellackia ptyodacryli
Schellackia weinbergi

Contents

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 visualised using a blood smear.

The type species, Schellackia bolivari , was described by Anton Reichenow in 1919.

History of knowledge

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 characterisation methods have allowed 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 utilises 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 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. [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]

Hosts and habitat

Schellackia species infect reptiles and amphibians all around the world, and is present in all continents except Antarctica. Although they have primarily been studied in lizards, they have been found to infect other animals including the Brazilian tree-frog, Phrynohyas venulosa . [8] The parasites are highly host specific, tending to infect a single host genus even when other lizard genera are present within the same geographical area. [6] Multiple species of Schellackia are named after their archetypal host, such as Schellackia occidentalis [5] and Schellackia agama . [7]

Description of the organism

Schellackia gametocytes are contained within parasitophorous vacuoles consisting of two membranes which are connected by numerous points of contact. The outer layer is thicker and bilaminate, while the inner layer comprises a single thinner structure. The vacuoles containing macrogametocytes are dense with fine granular material, while such material is largely absent from vacuoles containing microgametocytes. [9]

The microgametocytes and microgametes are contained within their own membrane within the vacuole. Developing microgametocytes have a peripheral nucleus without a visible nucleolus but contain dense patches of peripheral chromatin. The surface of the microgametocyte is covered in deep invaginations which provide increased surface area. Microgametes have flagella with a typical 9+2 axoneme structure, and five microtubules run parallel to the nucleus along the length of the gamete. [9]

Macrogametocytes are bound by a pellicle comprising two membranes perforated by multiple micropores. Two shapes of mitochondria are present – large, rounded mitochondria with tubular cristae are located beneath the pellicle, while smaller elongated mitochondria with a single row of cristae are present in aggregates. The nucleus is larger than the one found in microgametocytes and contains a large, compact nucleolus. The cytoplasm contains a dense RER network, as well as food, lipid, and other various vesicles. The presence of a high density of amylopectin granules in the cytoplasm causes it to have a foamy appearance, a characteristic maintained in the zygote. [7]

Schellackia sporozoites exist either free-floating or within a parasitophorous vacuole within a host cell. On occasion, multiple sporozoites have been observed to fit into a single expanded parasitophorous vacuole. The space within the vacuole surrounding the sporozoites contains a fine granular substance, and sometimes membranous residues. The sporozoites themselves are bound by a pellicle and contain a nucleus with a nucleolus and peripheral chromatin. One or two refractile bodies are also present, as well as multiple large mitochondria, amylopectin granules, and micronemes which extend from the apical tip along the length of the sporozoites. [10]

An important defining characteristic of the genus Schellackia is its octonucleate oocyst stage within the small intestine of a primary host – a combination of the presence of such oocysts as well as a lack of other parasites within the geographical area which share similar characteristics is sufficient to identify the genus. [11] The oocysts are enclosed in a translucent wall which are partially impermeable to Giemsa stain, and the cells leave behind empty rounded spaces upon expiration. [9]

Related Research Articles

<span class="mw-page-title-main">Apicomplexa</span> Phylum of parasitic alveolates

The Apicomplexa 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. The organelle is an adaptation that the apicomplexan applies in penetration of a host cell.

<i>Plasmodium</i> Genus of parasitic protists that can cause malaria

Plasmodium is a genus of unicellular eukaryotes that are obligate parasites of vertebrates and insects. The life cycles of Plasmodium species involve development in a blood-feeding insect host which then injects parasites into a vertebrate host during a blood meal. Parasites grow within a vertebrate body tissue before entering the bloodstream to infect red blood cells. The ensuing destruction of host red blood cells can result in malaria. During this infection, some parasites are picked up by a blood-feeding insect, continuing the life cycle.

<span class="mw-page-title-main">Plasmodiidae</span> Family of apicomplexan protists

The Plasmodiidae are a family of apicomplexan parasites, including the type genus Plasmodium, which is responsible for malaria. This family was erected in 1903 by Mesnil and is one of the four families in the order Haemospororida.

<i>Eimeria tenella</i> Species of single-celled organism

Eimeria tenella is a species of Eimeria that causes hemorrhagic cecal coccidiosis in young poultry. It is found worldwide.

<i>Eimeria</i> Genus of single-celled organisms

Eimeria is a genus of apicomplexan parasites that includes various species capable of causing the disease coccidiosis in animals such as cattle, poultry and smaller ruminants including sheep and goats. Eimeria species are considered to be monoxenous because the life cycle is completed within a single host, and stenoxenous because they tend to be host specific, although a number of exceptions have been identified. Species of this genus infect a wide variety of hosts. Thirty-one species are known to occur in bats (Chiroptera), two in turtles, and 130 named species infect fish. Two species infect seals. Five species infect llamas and alpacas: E. alpacae, E. ivitaensis, E. lamae, E. macusaniensis, and E. punonensis. A number of species infect rodents, including E. couesii, E. kinsellai, E. palustris, E. ojastii and E. oryzomysi. Others infect poultry, rabbits and cattle. For full species list, see below.

<span class="mw-page-title-main">Gregarinasina</span> Subclass of protists

The gregarines are a group of Apicomplexan alveolates, classified as the Gregarinasina or Gregarinia. The large parasites inhabit the intestines of many invertebrates. They are not found in any vertebrates. However, gregarines are closely related to both Toxoplasma and Plasmodium, which cause toxoplasmosis and malaria, respectively. Both protists use protein complexes similar to those that are formed by the gregarines for gliding motility and invading target cells. This makes them excellent models for studying gliding motility with the goal of developing treatment options for toxoplasmosis and malaria. Thousands of different species of gregarines are expected to be found in insects, and 99% of these gregarines still need to be described. Each insect can be the host of multiple species. One of the most studied gregarines is Gregarina garnhami. In general, gregarines are regarded as very successful parasites, as their hosts are spread over the entire planet.

<i>Leucocytozoon</i> Genus of protists

Leucocytozoon is a genus of parasitic alveolates belonging to the phylum Apicomplexa.

Megaloschizonts are large schizonts that produce extremely high numbers of merozoites. They are found in various species of the Phylum Apicomplexa. The Apicomplexa phylum contains several parasitic protozoans. They have a very complex life cycle that includes several stages. Megaloschizonts and the smaller schizonts are the part of the life cycle that takes place inside the infected host organism and operates as an asexually reproductive cell. Megaloschizonts appear as grey-white nodules found in the smooth muscle of major organs, such as the heart, liver, lung or spleen.

<span class="mw-page-title-main">Adeleorina</span> Suborder of microscopic, spore-forming, single-celled parasites in the aplcomplex phylum

Adeleorina is a suborder of parasites in the phylum Apicomplexa.

Karyolysus is a genus of coccidia. With the exception of K. sonomae whose vertebrate host is the yellow-legged frog, species in this genus only infect lizards of the genus Lacerta.

<span class="mw-page-title-main">Apicomplexan life cycle</span> Apicomplexa life cycle

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 typified by a cellular variety with a distinct morphology and biochemistry.

Acroeimeria is a genus of parasites that contains those species which initially develop immediately beneath the brush-border of the intestinal epithelium, but the meronts and gamonts of which are early on extruded to form a layer on the surface of the gut mucosa. Morphologically they are similar to the Eimeria to which they are closely related. The genus was described in 1989 by Paperna and Landsberg.

The genus Polychromophilus consists of obligate intracellular eukaryotic parasites that infect bats from every continent except Antarctica. They are transmitted by bat flies, which act as an insect vector as well as the parasite’s site of sporogeny. Polychromophilus follows a fairly typical Haemospororidian lifecycle, with gametocytes and gametes restricted to the bloodstream of the host and meronts infecting organs – most notably the lungs and the liver. The type species is Polychromophilus melanipherus, and was described by Dionisi in 1898.

Dactylosoma is a genus of parasitic alveolates of the phylum Apicomplexia.

Epieimeria is a genus of parasitic alveaolates of the phylum Apicomplexa.

Ovivora is a genus in the phylum Apicomplexa.

Merocystis is a genus in the phylum Apicomplexa.

Lankesterella is a genus in the phylum Apicomplexa. Species in this genus infect amphibians, reptiles and birds.

Mattesia is a genus of parasitic alveolates of the phylum Apicomplexa. Species in this genus infect insects.

Lipocystis is a genus of parasitic alveolates of the phylum Apicomplexa.

References

  1. ↑ Le Bail O, Landau I (1974) Description and experimental life cycle of Schellackia balli n. sp. (Lankesterellidae) a parasite of toads in Guyana. Ann Parasitol Hum Comp 49(6):663-668
  2. ↑ Finkelman, S.; Paperna, I. (2014). "Schellackia calotesi n. sp. from agamid lizards of the genus Calotes in Thailand". Parasite. 5 (1): 23–26. doi: 10.1051/parasite/1998051023 . ISSN   1252-607X. PMID   9754293. Open Access logo PLoS transparent.svg
  3. ↑ Lainson, R, Shaw JJ, Ward RD (1976) Schellackia landauae sp. nov. (Eimeriorina: Lankesterellidae) in the Brazilian lizard Polychrus marmoratus (Iguanidae): experimental transmission by Culex pipiens fatigans. Parasitol 11 (2)
  4. ↑ Bonorris, J.S., Ball, G.H.1955. Schellackia occidentalis n. sp., a blood-inhabiting coccidian found in lizards in Southern California. J Protozool 2: 31-34
  5. 1 2 3 BONORRIS, JIM S.; BALL, GORDON H. (February 1955). "Schellackia occidentalisn.sp., a Blood-inhabiting Coccidian Found in Lizards in Southern California". The Journal of Protozoology. 2 (1): 31–34. doi:10.1111/j.1550-7408.1955.tb02393.x. ISSN   0022-3921.
  6. 1 2 3 Megía-Palma, Rodrigo; Martínez, Javier; Cuervo, José J.; Jiménez-Robles, O.; Gomes, Verónica; Cabidof, C.; Fitzed, P.S.; Martina, J.; Merinoa, S. (2016). "Molecular diversity of the genus Schellackia (Apicomplexa: Schellackiidae) parasitizing lizards of the family lacertidae (squamata)". Molecular: 79.
  7. 1 2 3 4 5 6 7 Bristovetzky, Mariana; Paperna, Ilan (November 1990). "Life cycle and transmission of Schellackia cf. agamae, a parasite of the starred lizard Agama stellio". International Journal for Parasitology. 20 (7): 883–892. doi:10.1016/0020-7519(90)90026-j. ISSN   0020-7519.
  8. ↑ Paperna, I.; Lainson, R. (October 1995). "Schellackia (Apicomplexa: Eimeriidae) of the brazilian tree-frog, Phrynohyas venulosa (Amphibia: Anura) from Amazonian Brazil". Memórias do Instituto Oswaldo Cruz. 90 (5): 589–592. doi: 10.1590/s0074-02761995000500008 . ISSN   0074-0276.
  9. 1 2 3 Ostrovska, K.; Paperna, I. (1987). "Fine structure of gamont stages of Schellackia cf. agamae (Lankesterellidae, Eucoccidia) from the starred lizard Agama stellio". Parasitology Research. 73 (6): 492–499. doi:10.1007/bf00535322. ISSN   0044-3255.
  10. ↑ Paperna, I. (April 1993). "Electron microscopic study of Schellackia cf. agamae sporozoite infection in mosquitoes". International Journal for Parasitology. 23 (2): 187–190. doi:10.1016/0020-7519(93)90140-t. ISSN   0020-7519.
  11. ↑ Telford, Sam R. (June 1993). "A species of Schellackia (Apicomplexa: Lankesterellidae) parasitising east and southeast Asian lizards". Systematic Parasitology. 25 (2): 109–117. doi: 10.1007/bf00009980 . ISSN   0165-5752.
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