Difference between revisions of "Trichinella"

Revision as of 17:29, 8 June 2011

Trichinella spiralis stained with H and E - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine

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Trichinella in tissues. Wikimedia commons.

Introduction

Trichinella spiralis is a helminth parasite of the Trichinelloidea superfamily. It is unique among helminths as it is intracellular and requires only one host.

Disease is most important in pigs and wild boar due to its zoonotic transmission through eating pork. Trichinellosis is a serious public health hazard.

The trichinae are widespread across all continents. T. spiralis is found in temperate Europe, Asia, New Zealand, North and South America.

This disease is notifiable to the World Organisation for Animal Health (OIE)

Lifecycle

The lifecycle of T. spiralis is direct.

Larvae are ingested by the pig through scavenging or predation. Free range outdoor pigs are therefore at highest risk.

Gastric digestion releases the larvae from the infected muscle tissue.

They then undergo moults and copulate in the small intestine after which the males die and the females penetrate into the intestinal mucosa.

The females then produce more larvae which can disseminate through the host in the blood and lymphatics, localising in the striated muscles. In pigs and wild boars, preferential sites appear to be the diaphragm, masseters and tongue.

The muscle cells are transformed by the larvae within them, to form nurse cells which can supply nutrition and protects the larvae in a collagen capsule.

Larvae can then survive in frozen and decaying carcasses form an important route of transmission.

Humans are infected by eating raw or undercooked meat containing the infective larvae.

Pathogenesis

Damage is caused by penetrating female larvae in the small intestine and dissemination of larvae into the muscle masses. The degree of damage is dependent upon pathogen load.

Diagnosis

Direct microscopy of muscle samples between two glass plates can detect the organism.

Digestion with pepsin-HCl is also possible.

ELISA testing is also available.

Diseases

Trichinellosis is usually subclinical in pigs, forming muscular cysts.

Large burdens may cause enteritis followed by myositis, fever and myocarditis which can be fatal.

Human disease is serious and sometimes fatal, causing myositis, myocarditis, encephalitis and facial oedema.

Control

Anthelminthics can be used both as a treatment and control method for trichinellosis.

Prevention of scavenging and feeding appropriate feedstuffs to pigs.

Meat inspection and destruction wherever trichinellosis is found.

References

Animal Health & Production Compendium, Trichinella datasheet, accessed 08/06/2011 @ http://www.cabi.org/ahpc/

@@ Line 2: / Line 2: @@
 [[File:Trichinella larvaeD.jpg|thumb|200px|right|''Trichinella'' in tissues. Wikimedia commons.]]
-==Overview==
+==Introduction==
-*This is known as the "worm that thinks its a virus"
+''Trichinella spiralis'' is a '''[[Helminths | helminth]] parasite''' of the ''[[Trichinelloidea]]'' superfamily.
-*It is an important zoonosis
+It is unique among helminths as it is '''intracellular''' and requires '''only one host'''.
-*It is covered in greater detail
-*''Trichinella'' in [[Parasitic Myositis#Nematodes|myositis]]
+Disease is most important in pigs and wild boar due to its '''zoonotic''' transmission through eating '''pork'''. Trichinellosis is a '''serious public health hazard'''.
-== Trichinosis ==
+The trichinae are widespread across all continents.
-''Trichinella'' is a serious public health hazard and could occur at any time in the UK.
+''T. spiralis'' is found in temperate Europe, Asia, New Zealand, North and South America.
+This disease is '''notifiable''' to the World Organisation for Animal Health [http://www.oie.int/ (OIE)]
-=== '''''TRICHINELLA SPIRALIS''''' ===
+==Lifecycle==
-*This is very rare in British pigs, if it occurs at all.
+The lifecycle of ''T. spiralis'' is direct.
-*Free-range pigs are at greatest risk of becoming infected.
-*Infections are asymptomatic in the pig.
-*It is an important zoonosis, with 6500 human cases in the EU between 1966 and 2001.
-*Human disease is serious and sometimes fatal, with myositis, myocarditis, encephalitis and facial oedema.
-*Human cases are most often, but not invariably, associated with pigs.
-*Other meat animals can also be the source of human infection, e.g. horses in France and Italy, wild boar in Eastern Europe, bears in North America, walruses in the Arcitc.
-*The last human trichinosis epidemic in Britain occurred some 50years ago.
-==== Life-Cycle ====
+Larvae are ingested by the pig through scavenging or predation. '''Free range''' outdoor pigs are therefore at highest risk.
-Encysted larvae are eaten by an animal. The adult worm develops, and then enters the small intestine. The larve migrate through the blood, via the lymphatics, to striated muscle, where the larvae develop to the infective stage.
-*''T. spiralis'' can infect a wide variety of mammals.
+[[Monogastric Stomach - Anatomy & Physiology | '''Gastric digestion''']] releases the larvae from the infected muscle tissue.
-*The adults are only approximately 3mm long, and are closely applied to the mucosa of the small intestine.
-*The life-cycle is unique in two respects:
-**it uses the '''same individual''' firstly as the '''final''', and then '''intermediate host'''
-**the larvae are ''' intracellular'''.
-==== Epidemiology of Trichinosis ====
+They then undergo moults and '''copulate''' in the '''small intestine''' after which the males die and the '''females penetrate''' into the intestinal '''mucosa'''.
-There are several species of ''Trichinella'', each with a different host range and slightly different biological characteristics. There are domestic and sylvatic cycles. ''T. spiralis'' is the species that most often affects pigs and humans.
-*In '''sylvatic cycles''':
+The females then produce more '''larvae''' which can '''disseminate''' through the host in the blood and lymphatics, localising in the '''striated muscles'''. In pigs and wild boars, preferential sites appear to be the '''diaphragm, masseters and tongue.'''
-**the infection is transmitted within some wildlife populations (e.g. rats) and ascends food-chains to the top carnivores and omnivores (e.g. the fox in Europe)
-**carnivores and omnivores are particularly vulnerable, but herbivores can be infected if they accidentally ingest meat (e.g. remains of dead mouse in hay).
-**other ''Trichinella'' species occur in wildlife. For example, one infects arctic marine mammals and polar bears (and is highly infective for humans), while another is restricted to some East African fauna (and does not infect humans). A new species has recently been discovered in crocodiles.
-*In the '''domestic cycle''':
+The muscle cells are transformed by the larvae within them, to form '''nurse cells''' which can supply '''nutrition''' and protects the larvae in a '''collagen capsule'''.
-**the main source of infection for pigs is undercooked swill containing kitchen waste
-**humans are most often infected by eating undercooked pork or pork products
-**one pig is eaten by more than 1000 people, which can therefore lead to mini-epidemics (common source outbreaks)
-**recent outbreaks in France and Italy have been traced to meat from horses fed offal-based diets before importation from Eastern Europe.
-==== Control ====
+Larvae can then survive in frozen and decaying carcasses form an important route of transmission.
-The main principles of control are:
-) Pigs must not be allowed to scavenge
+Humans are infected by eating '''raw or undercooked meat''' containing the infective larvae.
-) Meat inspection:
+==Pathogenesis==
+Damage is caused by '''penetrating female larvae''' in the small intestine and '''dissemination of larvae''' into the muscle masses. The degree of damage is dependent upon pathogen load.
-a. Destruction of infected carcasses protects human health and reduces the risk of contaminated swill being fed to pigs
+==Diagnosis==
+'''Direct microscopy''' of muscle samples between two glass plates can detect the organism.
-b. Detection methods include microscopic examination of diaphragm muscle (trichinoscope); pepsin digestion of diaphragm muscle; ELISA on blood - used mostly for epidemiological surveys
+Digestion with '''pepsin-HCl''' is also possible.
-) Boil swill adequately (compulsory in the UK)
+'''[[ELISA testing]]''' is also available.
-) Pork products must be well cooked or otherwise treated before human consumption.
+==Diseases==
+Trichinellosis is usually '''subclinical in pigs''', forming muscular cysts.
+Large burdens may cause '''enteritis''' followed by '''[[Parasitic Myositis | myositis]]''', fever and '''[[Myocarditis | myocarditis]]''' which can be fatal.
-**Particularly in pigs and dogs
+'''Human disease''' is serious and sometimes fatal, causing '''myositis, myocarditis, encephalitis and facial oedema.'''
-**Public health and economic importance
-**''T. spiralis'' affecting dogs, pigs, cats and humans is most common in hotter climates
-**Larvae distend myofibres
-**May be seen grossly if dead and calcified
-**Predilection for active muscles, ''e.g.'' diaphragm, intercostal, masseter and tongue muscles
-**Histologically:
-***Focal myositis - [[Neutrophils|neutrophils]], lymphocytes, eosinophils
+==Control==
+'''[[Anthelminthics]]''' can be used both as a treatment and control method for trichinellosis.
+Prevention of scavenging and feeding appropriate feedstuffs to pigs.
+Meat inspection and destruction wherever trichinellosis is found.
+==References==
+<references/>
+Animal Health & Production Compendium, '''Trichinella datasheet''', accessed 08/06/2011 @ http://www.cabi.org/ahpc/
 [[Category:Trichinelloidea]]
-[[Category:Pig_Nematodes]][[Category:Zoonoses]]
+[[Category:Pig_Nematodes]][[Category:Zoonoses]][[Category:To Do - Steph]]
-[[Category:To_Do_-_Steph]]