Medical protozoology: Apicomplexa

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A note on taxonomy

Adl et al. 2012 The revised classification of eukaryotes.

A note on taxonomy Adl et al. 2012 The revised classification of
The Journal of Eukaryotic Microbiology. 59(2), 429 – 493.

Taxonomy  is the science of defining groups of biological organisms on the basis of shared characteristics and giving names to those groups. 
Practical application
Understanding evolution of life

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Morphology-based taxonomy

Depending on the locomotion mode protozoa divided into four major groups:

Morphology-based taxonomy Depending on the locomotion mode protozoa divided into four major

Phylum Flagellates (move by means of flagella)

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Morphology-based taxonomy

Depending on the locomotion mode protozoa divided into four major groups:

Morphology-based taxonomy Depending on the locomotion mode protozoa divided into four major

Phylum Amoebae (by pseudopodia)

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Morphology-based taxonomy

Depending on the locomotion mode protozoa divided into four major groups:

Morphology-based taxonomy Depending on the locomotion mode protozoa divided into four major

Phylum Ciliates (by cilia)

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Morphology-based taxonomy

Depending on the locomotion mode protozoa divided into four major groups:

Morphology-based taxonomy Depending on the locomotion mode protozoa divided into four major

Phylum Sporozoa (lacking any obvious means of locomotion)

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Parasitic Apicomplexa (former Sporozoa)

The apicomplexa are a monophyletic group composed almost entirely

Parasitic Apicomplexa (former Sporozoa) The apicomplexa are a monophyletic group composed almost
of parasitic (ie, no free-living) species.
Apicomplexa, along with ciliates and dinoflagellates, form a higher order group known as Alveolata.
A major defining characteristic of the this group are flattened vesicle-like structures, called cortical alveolae, which are found just underneath the plasma membrane.
Formerly the apicomplexa were part of a group called Sporozoa and this name is still sometimes used.

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Parasitic Apicomplexa

 A defining characteristic of the apicomplexa is a group of

Parasitic Apicomplexa A defining characteristic of the apicomplexa is a group of
organelles found at one end--called the apical end--of the organism.
This is a type of plastid called an apicoplast, and anapical complex structure involved in penetrating a host's cell.

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Parasitic Apicomplexa

 This 'apical complex' includes secretory organelles known as micronemes and

Parasitic Apicomplexa This 'apical complex' includes secretory organelles known as micronemes and
rhoptries, polar rings composed of microtubules, and in some species a conoid which lies within the polar rings.

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Parasitic Apicomplexa

At some point during their life cycle, members of the

Parasitic Apicomplexa At some point during their life cycle, members of the
apicomplexa either invade or attach to host cells.
It is during this invasive (and/or motile) stage that these apical organelles are expressed as well as the subpellicular membranes, which are actually cortical alveoli.
The apical organelles play a role in interaction of the parasite with the host cell and the subsequent invasion of the host cell.
Motile forms of apicomplexa crawl along the substratum in a non-ameboid fashion known as gliding motility. Many apicomplexan species have flagellated gametes.

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Parasitic Apicomplexa

The apicomplexa have complex life cycles that are characterized by

Parasitic Apicomplexa The apicomplexa have complex life cycles that are characterized by
three distinct processes: sporogony, merogony and gametogony .

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Parasitic Apicomplexa

Although most apicomplexa exhibit this overall general life cycle the

Parasitic Apicomplexa Although most apicomplexa exhibit this overall general life cycle the
details can vary between species.
Furthermore, the terminology used to describe these various life cycle stages vary between the species.
The life cycle consists of both asexually reproducing forms and sexual stages.

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Parasitic Apicomplexa

In monoxenous species all three of these processes will be

Parasitic Apicomplexa In monoxenous species all three of these processes will be
carried out in a single host and often in a single cell type or tissue.
Whereas, in heteroxenous species the various processes will be carried out in different hosts and generally involve different tissues.

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Parasitic Apicomplexa

Sporogony occurs immediately after a sexual phase and consists of

Parasitic Apicomplexa Sporogony occurs immediately after a sexual phase and consists of
an asexual reproduction that culminates in the production of sporozoites.
Sporozoites are an invasive form that will invade cells and develop into forms that undergo another asexual replication known as merogony.

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Parasitic Apicomplexa

Merogony and the resulting merozoites are known by many different

Parasitic Apicomplexa Merogony and the resulting merozoites are known by many different
names depending of the species. In contrast to sporogony, in which there is generally only one round of replication, quite often there are multiple rounds of merogony.
In other words, the merozoites, which are also invasive forms, can reinvade cells and initiate another round of merogony.

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Parasitic Apicomplexa

As an alternative to asexual replication merozoites can develop into

Parasitic Apicomplexa As an alternative to asexual replication merozoites can develop into
gametes through a process variously called gametogony, gamogony or gametogenesis.
As in other types of sexual reproduction, the gametes fuse to form a zygote which will undergo sporogony.

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Parasitic Apicomplexa

The apicomplexa are an extremely large and diverse group (>5000

Parasitic Apicomplexa The apicomplexa are an extremely large and diverse group (>5000
named species). Seven species infect humans.
Plasmodium
Babesia
Cryptosporidium
Isospora
Cyclospora
Sarcocystis
Toxoplasma

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Parasitic Apicomplexa

Plasmodium, as the causative agent of malaria, has the greatest

Parasitic Apicomplexa Plasmodium, as the causative agent of malaria, has the greatest
impact on human health.
Babesia is a relatively rare zoonotic infection.
The other five species are all classified as coccidia. However, recent molecular data indicates that Cryptosporidium is more closely related to the gregarines than to the coccidia. The coccidia are generally considered opportunistic pathogens and are often associated with AIDS.

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Parasitic Apicomplexa

Several apicomplexan parasites are also important in terms of veterinary

Parasitic Apicomplexa Several apicomplexan parasites are also important in terms of veterinary
medicine and agriculture. Most notable are Babesia and Theileria in cattle and Eimeria in poultry.

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Parasitic Apicomplexa

Diseases caused by apicomplexan organisms include, but are not limited

Parasitic Apicomplexa Diseases caused by apicomplexan organisms include, but are not limited
to:
Forms of coccidiosis including:
Cryptosporidiosis (Cryptosporidium parvum)
Cyclosporiasis (Cyclospora cayetanensis)
Isosporiasis (Isospora belli)
Toxoplasmosis (Toxoplasma gondii)
Malaria (Plasmodium)
Babesiosis (Babesia)
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