|
|
| (27 intermediate revisions by 4 users not shown) |
| Line 1: |
Line 1: |
| − | {{toplink
| + | #REDIRECT[[:Category:Protozoa]] |
| − | |backcolour =
| |
| − | |linkpage =Infectious agents and parasites
| |
| − | |linktext =INFECTIOUS AGENTS AND PARASITES
| |
| − | |pagetype=Bugs
| |
| − | |sublink1=Parasites
| |
| − | |subtext1=PARASITES
| |
| − | }}
| |
| − | | |
| − | ==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.
| |
| − | | |
| − | Not all protozoa are harmful. For example, the [[The Rumen - Anatomy & Physiology|rumen]] of ruminants and the [[Caecum - Anatomy & Physiology|caeca]] and [[Colon - Anatomy & Physiology|colon]] of horses are full of symbiotic protozoa.
| |
| − | | |
| − | ==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==
| |
| − | [[Image:Balantidium pig trophozoite.jpg|thumb|right|150px|''Balantidium'' trophozoite from a pig - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
| |
| − | | |
| − | *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''
| |
| − | | |
| − | [[Cryptosporidium|Cryptosporidium]]
| |
| − | | |
| − | [[Giardia]]
| |
| − | | |
| − | [[Piroplasmida]]
| |
| − | *Babesia
| |
| − | *Cytauxzoon
| |
| − | *Theileria
| |
| − | | |
| − | [[Tissue cyst-forming coccidia]]
| |
| − | *''Neospora''
| |
| − | *''Sarcocystis''
| |
| − | *''Toxoplasma''
| |
| − | | |
| − | [[Tropical Protozoa]]
| |
| − | *''Leishmania'' spp.
| |
| − | *''Trypanosoma'' spp.
| |
| − | | |
| − | [[Other Important Protozoa]]
| |
| − | *''Balantidium''
| |
| − | *''Cyclospora''
| |
| − | *''Entamoeba''
| |
| − | *''Histomonas meleagridis''
| |
| − | *''Microsporidia''
| |
| − | *''Tritrichomonas foetus''
| |
| − | | |
| − | ==Useful Resources==
| |
| − | *http://www.veterinariavirtual.uab.es/parasito/diagnos003$/coproeq.htm
| |
| − | ''Brilliant microscopic pictures of protozoa and helminths''
| |
| − | | |
| − | *http://www.vet.uga.edu/VPP/clerk/siegel/index.php
| |
| − | ''Detailed information and images, including clincial signs and pathogenesis, of East Coast Fever''
| |