Difference between revisions of "Nematodes"

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== Introduction ==
 
Nematodes are one of the most prolific life-forms on this planet. Most are free-living, with species adapted to every imaginable habitat. Some are parasitic on plants, and others on animals. The animal parasitic nematodes form a large and diverse array of organisms.
 
 
 
 
 
== The Nematodes ==
 
=== Recognition Features ===
 
*A unique feature of the nematodes is that the fluid in the body cavity is maintained under high pressue (this is why nematodes often burst after collection).
 
*They therefore have a tough elastic cuticle which often forms elaborate structures useful for identification.
 
*A muscular pharynx is needed to pump food into the intestine.
 
*The shape of the pharynx is characteristic in some groups.
 
*There is a nerve ring around the pharynx and four longitudinal nerves with ganglia that co-ordinate movement (many anthelmintics act by disrupting neuromuscular co-ordination).
 
*The sexes are separate:
 
**the female tail generally ends in a blunt point
 
**males usually have two chitinous rods that can be protruded through the cloaca to hold the female - these are called spicules and, being chitinous, are easily seen under the microscope. As they differ in shape and size between species, they are very useful for identification.
 
*The '''bursate nematodes''' are characterised by a large expansion of the cuticle of the male tail to form a clasping organ (the bursa).
 
*Other modifications of the cuticle on both male and female nematodes useful for identification include:
 
**'''alae''' (wing-like protrusions)
 
**'''vesicles''' (swellings around the whole circumference of the body).
 
*The heads of some nematodes have structures such as:
 
**leaf-like lips around the mouth (the '''leaf-crown''')
 
**a '''buccal cavity'''
 
**'''teeth''' or '''cutting plates'''.
 
 
 
 
 
=== Feeding Habits ===
 
*Many intestinal nematodes are closely applied to the mucosal surface.
 
*Some swallow ingesta and/or host secretions.
 
*Others suck a plug of mucosa into the buccal cavity (plug feeders), leaving a circular ulcer.
 
*Yet others bury their heads deep into the mucosa and suck blood.
 
 
 
 
 
=== General Life-Cycle ===
 
*The basic life-cycle is very simple:
 
 
 
egg → L1 → L2 → L3 → L4 → adult
 
 
 
*With a moult in between each larval stage.
 
*But there are many variations on this theme!
 
 
 
 
 
=== Nematode Eggs ===
 
These vary greatly in appearance and are very useful for diagnosis as they can often be detected and counted in faecal samples.
 
 
 
NOTE: we use the typical '''strongyle''' egg to provide us with a yard-stick for comparing sizes. A "large egg", for example, means larger than a strongyle egg. A typical strongyle egg is approximately '''80µm''' long.
 
 
 
 
 
== Nematode Superfamilies ==
 
'''BURSATE'''
 
 
 
*[[Trichostrongyloidea]]
 
 
 
*[[Strongyloidea]]
 
 
 
*[[Ancylostomatoidea]] (Hook worms)
 
 
 
*[[Metastrongyloidae]]
 
 
 
NOTE: the Trichostrongyloidea, Strongyloidea and hookworms are very closely related, and are often collectively known as '''"the strongyles"'''. Typically, they produce almost identical eggs, called '''"typical strongyle eggs"'''.
 
 
 
'''NON-BURSATE'''
 
 
 
*[[Ascaridoidea]]
 
 
 
*[[Oxyuroidea]]
 
 
 
*[[Rhabditoidea]]
 
 
 
*[[Trichinelloidea]]
 
 
 
*[[Spiruroidea]]
 
 
 
*[[Filarioidea]]
 
 
 
 
 
From the veterinary view-point, the nematodes are most conveniently grouped into '''superfamilies''' because their members often have similar life-cycles and epidemiological features. Superfamily names end in -oidea (the anglicised form is -oid, as in trichostrongyloid).
 
 
 
 
 
 
 
 
 
 
 
 
 
Occlusion of pancreatic ducts sometimes happens [[Pancreas Parasitic - Pathology]]
 

Latest revision as of 21:17, 13 July 2010

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