Difference between revisions of "Protozoa"

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#REDIRECT[[:Category:Protozoa]]
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|linkpage =Infectious agents and parasites
 
|linktext =INFECTIOUS AGENTS AND PARASITES
 
|pagetype=Bugs
 
|sublink1=Parasites
 
|subtext1=PARASITES
 
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==Introduction==
 
[[Image:Balanditium.jpg|thumb|right|150px|Balantidium coli - trofozoite and cyst - Wikimedia Commons]]
 
[[Image:Flagella.jpg|thumb|right|150px|Flagella of ''E.coli'' - Nicolle Rager Fuller, National Science Foundation]]
 
All protozoa are unicellular eukaryotic organisms which store their genetic information in chromosomes in a nuclear envelope. Protozoa are classified depending on their structure and life cycle. This reflects the similarities of the diseases which they cause.
 
 
 
Protozoa usually range from 10μm-50μm but can grow up to 1mm. Thus, they are usually observed and classified using a microscope.
 
 
 
Protozoa multiply sexually, asexually and can also use a combination of both, for example, the coccidia class. Replication can be by binary or multiple fission. Different protozoa use different forms of motility, including flagella, cilia, pseudopodia and gliding.
 
 
 
==Structure and function==
 
 
 
*Motile
 
 
 
*Organelles and otehr cellular structures enable the protozoa to lead an '''independent exsistence'''
 
 
 
*Cilia
 
**Fine, short hairs covering the protozoal surface
 
**Hairs beat in unison to enable the protozoa to move
 
**Wafts food towards the cytostome (mouth opening)
 
**E.g. ''Balantidium''
 
 
 
*Flagellum
 
**Contractile fibre
 
**Contracts in a whip like motion to propel protozoa
 
**Attached to body of protozoa by an '''undulating membrane'''
 
**E.g. ''Trypanosoma''
 
 
 
*Pseudopodia
 
**Extensions of the cellular cytoplasm
 
**Cytoplasm flows into the pseudopodia allowing movement of the protozoa
 
**Also acts in a phagocytic manner surrounding food particles and enclosing it in a vacuole
 
**E.g. ''Entamoeba''
 
 
 
*Gliding
 
**No obvious means of locomotion
 
**E.g. ''Eimeria''
 
 
 
==Nutrition and digestion==
 
[[Image:Pinocytosis.jpg|thumb|right|150px|Pinocytosis - Mariana Ruiz Villarreal]]
 
*Pinocytosis
 
**Droplets of fluid taken into the cell
 
**Generates small vesicles
 
**Usually used for extracellular fluid ingestion
 
**Requires ATP
 
 
 
*Phagocytosis
 
**Larger particles of matter taken into the cell
 
**Usually solid particles ingested
 
 
 
*Cell membrane envelops the fluid or food taking it into the cell
 
 
 
*Lysosomes fuse with the fluid/food initiating digestion
 
 
 
*Diffusion through the cell membrane allows excretion of metabolic products
 
 
 
==Life Cycle==
 
 
 
*Most protzoal reproduction is asexual using binary fission, schizogony and sporogony
 
 
 
*Some protozoa also use sexual reproduction called gametogony
 
 
 
*In some species, sexual and asexual reproduction occurs in the same host, whilst in others asexual reproduction occurs in the vertebrate host and sexual reproduction in the arthropod vector
 
 
 
*Homogenous
 
**Parasite uses a single host species during its life cycle (direct)
 
**E.g. ''Eimeria''
 
 
 
*Heteroxenous
 
**Parasite uses more than one host during its life cycle (indirect)
 
**E.g. ''Trypanosomes''
 
 
 
*Facultatively heteroxenous
 
**Parasite '''may''' use more than one host during its life cycle but this is not essential
 
**E.g. ''Toxoplasma gondii''
 
 
 
===Example of a Protozoal Life Cycle===
 
[[Image:Coccidia.jpg|thumb|right|150px|Coccidia - Joel Mills]]
 
''The following refers specifically to the life cycle of Coccidia spp.''
 
*The '''oocyst''' is the resistant stage in the environment
 
 
 
*The infective '''sporozoite''' is released from the oocyst
 
 
 
*Inside the host, the sporozoites invade the intestinal epithelial tissue
 
**Sporozoites feed and grow
 
 
 
*As the sporozoites grow the nucleus divides forming a '''schizont'''
 
 
 
*The schizont contains numerous elongated '''merozoites'''
 
 
 
*The formation of merozoites is the first asexual reproductive stage called '''schizogony'''
 
 
 
*The schozont ruptures releasing the merozoites which also invade the epithelial cells
 
 
 
*Another generation of schizonts form which is the beginning of the sexual phase of reproduction called '''gametogeny'''
 
 
 
*The merozoites form male '''microgamonts''' or female '''macrogamonts'''
 
**Collectively known as gamonts or gametocytes
 
 
 
*The microgamonts released from the microgametocyte penetrate and fertilise the macrogamete (which is contained within the macrogametocyte)
 
 
 
*Gametogeny forms the '''zygote'''
 
**Surrounded by a cyst wall
 
**Forms the '''oocyst'''
 
 
 
*The oocyst is passed in the faeces as unsporulated
 
 
 
*The oocyst becomes sporulated in the second asexual reproductive phase called '''sporogeny'''
 
 
 
*Once the oocyst is sporulated it is infective
 
 
 
==Protozoa of Veterinary Importance==
 
 
 
[[Coccidia]]
 
*''Eimeria''
 
*''Isospora''
 
 
 
[[Tissue cyst-forming coccidia]]
 
*''Toxoplasma''
 
*''Neospora''
 
*''Sarcocystis''
 
 
 
[[Piroplasmida]]
 
 
 
[[Cryptosporidium|Cryptosporidium and Cyclospora]]
 
 
 
[[Babesia]]
 
 
 
[[Tropical Protozoa]]
 
*''Theileria'' spp.
 
*''Trypanosoma'' spp.
 
*''Leishmania'' spp.
 
 
 
[[Giardia]]
 
 
 
[[Other Important Protozoa]]
 
*''Tritrichomonas foetus''
 
*''Histomonas meleagridis''
 
*''Balantidium''
 
*''Entamoeba''
 
*''Microsporidia''
 
 
 
==Useful Resources==
 
*http://www.veterinariavirtual.uab.es/parasito/diagnos003$/coproeq.htm
 
''Brilliant microscopic pictures of protozoa and helminths''
 

Latest revision as of 19:07, 18 May 2010

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