Difference between revisions of "Protozoa"

Revision as of 19:16, 15 November 2008

INFECTIOUS AGENTS AND PARASITES PARASITES

Introduction

Balantidium coli - trofozoite and cyst - Wikimedia Commons

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

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

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
Cryptosporidium
Cyclospora
Isospora

Tissue cyst-forming coccidia

Toxoplasma
Neospora
Sarcocystis

Theileria spp.
Trypanosoma spp.
Leishmania spp.

Giardia

Other Important Protozoa

Tritrichomonas foetus
Histomonas meleagridis
Balantidium
Entamoeba
Microsporidia

@@ Line 1: / Line 1: @@
-#REDIRECT[[:Category:Protozoa]]
+{{toplink
+|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.
+==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''
+*''Cryptosporidium''
+*''Cyclospora''
+*''Isospora''
+[[Tissue cyst-forming coccidia]]
+*''Toxoplasma''
+*''Neospora''
+*''Sarcocystis''
+[[Piroplasmida]]
+[[Cryptosporidium]]
+[[Babesia]]
+[[Tropical Protozoa]]
+*''Theileria'' spp.
+*''Trypanosoma'' spp.
+*''Leishmania'' spp.
+[[Giardia]]
+[[Other Important Protozoa]]
+*''Tritrichomonas foetus''
+*''Histomonas meleagridis''
+*''Balantidium''
+*''Entamoeba''
+*''Microsporidia''