Difference between revisions of "Tissue cyst-forming coccidia"

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[[Neospora]]
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#REDIRECT[[:Category:Tissue Cyst Forming Coccidia]]
 
 
 
 
[[Sarcocystis]]
 
 
 
 
 
==Toxoplasma==
 
[[Image:Toxoplasma gondii.jpg|thumb|right|150px|''Toxoplasma gondii'' - Ke Hu and John Murray]]
 
[[Image:Toxoplasma sporulated oocyst.jpg|thumb|right|150px|''Toxoplasma'' Sporulated Oocyst - Wikimedia Commons]]
 
[[Image:Toxoplasma Tacchyzoites.jpg|thumb|right|150px|''Toxoplasma'' Tacchyzoites - Wikimedia Commons]]
 
[[Image:Toxoplasma Life Cycle.jpg|thumb|right|150px|''Toxoplasma'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
 
[[Image:Toxoplasma gondii 2.jpg|thumb|right|150px|''Toxoplasma gondii'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]
 
*Major pathogenic species called ''Toxoplasma gondii''
 
 
 
*Causes disease in a wide range of animal species including humans
 
 
 
*Important cause of abortion in sheep
 
 
 
*Zoonotic
 
**Can cause abortion
 
**Can cause congenitally aquired defects
 
 
 
*Forms a sporulated oocyst which is only 10μm
 
**Contains 2 sporocysts with 4 sporozoites
 
 
 
*Transmission through ingesting the intermediate host or via the faecal-oral route
 
 
 
'''Life Cycle'''
 
*Complex
 
 
 
*Usually indirect
 
**Referred to as '''facultatively heteroxenous'''
 
**Intermediate host is not essential for completion of the life cycle
 
 
 
*Gametogony (sexual stage) is host specific for felids
 
 
 
*Any warm blooded animal can act as a facultative intermediate host
 
**Asexual reproduction occurs in the intermediate host forming tissue cysts
 
**Intermediate host swallows sporulated oocysts or tissue cysts
 
**Can be transferred between intermediate hosts by carnivorism
 
 
 
*Cats
 
**Sporulation occurs in 2-3 days
 
**Cats either swallow infective (sporulated) oocysts where ''Toxoplasma gondii'' has a prepatent period of 3 weeks
 
**Or eat the tissues of an infected intermediate host where ''Toxoplasma gondii'' has a prepatent period of 3-10 days
 
**Self-limiting infection
 
**Oocysts are shed for 1-2 weeks
 
***Shedding can occur later if immunity wanes or cat is immuno-compromised
 
 
 
*Intermediate host
 
**3 sources of infection
 
***Oocysts from environment contaminated by cat faeces
 
***Eating cysts in tissues of other infected hosts through carnivorism or undercooked meat
 
***Transplacental transmission in some host species during the acute phase of infection
 
 
 
*Acute phase of infection
 
**After infection of the intermediate host the organism undergoes a phase of rapid division and dissemination throughout the body
 
***Parasite enters cell and asexual reproduction occurs by '''endodyogeny''' (budding) producing 8-16 '''tachyzoites'''
 
***Tachyzoites are released when host cell bursts
 
***Haematogenous spread as more cells are infected
 
***Infection continues until the animal develops immunity (around 2 weeks) at which point the infection enters the chronic phase
 
 
 
*Chronic phase of infection
 
**Occurs once the host's immune response has become effective
 
***Groups of slow growing intracellular '''bradyzoites''' become walled off forming infective '''cysts'''
 
***Bradyzoites inside cysts are protected from the host immune response whereas extracellular tachyzoites are killed
 
***Cysts remain viable for months to years and are particularly numerous in muscle and nervous tissue
 
***If immunity is suppressed the infection can revert to the acute form
 
 
 
'''Pathogenesis'''
 
*Cat
 
**In the intestinal phase of infection only the superficial cells at the tips of the villi are affected
 
**Little significant pathogenicity
 
 
 
*Sheep
 
**Mostly asymptomatic
 
**However, if a non-immune ewe is infected during pregnancy the consequences will be serious
 
***Infection during the first trimester leads to resorption
 
**Infection during the second trimester leads to foetal death and mummification
 
**Infection during the last trimester leads to a weak or stillborn lamb
 
**Aborted ewes show focal necrotic placentitis with white lesions in the cotyledons and foetal tissue
 
**Diagnosis is confirmed by Giemsa and serology of the ewe's blood
 
 
 
*Clinical outbreaks of toxoplasmosis are '''sporadic'''
 
**Immunity is acquired before tupping
 
**Significant ill-effects are unlikely if immune ewes are infected during pregnancy
 
**Not shed from sheep to sheep so predicting outbreaks is difficult
 
 
 
*Humans
 
**Mostly asymptomatic
 
**Virulent strains cause flu-like symptoms, malaise and/or lymphadenopathy
 
**In immunodeficient patients, disease can even be caused by avirulent strains
 
**If a non-immune women is infected during pregnancy, abortion or the birth of a congenitally infected child can result
 
***E.g. Hydrocephalus, opthalmitis, mental retardation
 
 
 
*Dogs
 
**Complication of canine distemper
 
**Causes [[Respiratory Parasitic Infections - Pathology#Toxoplasmosis|pneumonia]] and encephalitis
 
 
 
*Cattle and horses
 
**Sometimes infectious causing opthalmitis
 
 
 
*Toxoplasma can cause [[Pancreas Inflammatory - Pathology#Acute haemorrhagic pancreatitis|acute interstitial pancreatitis]] in systemic toxoplasmosis
 
 
 
*''Toxoplasma gondii'' causes [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
 
 
 
'''Epidemiology'''
 
*Serology
 
**Sabin-Feldman Dye test (old method)
 
**ELISA
 
**Mouse inoculation for confirmation
 
 
 
*Cat
 
**30-80% test seropositive
 
**Each cat sheds oocysts for 1-2 weeks of its life
 
 
 
*Human
 
**30% seropositive in UK, 70% seropositive in France
 
 
 
*Meat animals
 
**Significant proportion of cattle, sheep, pigs and rabbits can tissue cysts
 
 
 
'''Prevention'''
 
*Cat
 
**Impossible if cat is allowed outdoors due to hunting
 
**If kept indoors, only canned food should be fed and vermin controlled
 
**ELISA to check if seropositive
 
 
 
*Human
 
**Avoid oocyst ingestion
 
***Wash potentially contaminated raw food thoroughly
 
***Wash hands after gardening or handling cats and especially before eating
 
***Clean out cat litter trays every day before oocysts sporulate
 
**Avoid ingestion of tissue cysts
 
***Do not eat undercooked meat
 
***Wash hands after handling raw meat
 
***Take care when lambing or dealing with sheep abortions and stillbirths
 
***Pregnant women should avoid lambing altogether
 
 
 
*Sheep
 
**Toxovax vaccine
 
***Live, avirulent strain of ''Toxoplasma''
 
***Does not form bradyzoites or tissue cysts
 
***Killed by host immune system
 
***Single dose given 6 weeks before tupping
 
***Protects for 2 years
 
***Immunity boosted by natural challenge
 
**Medicated feed can be given daily during the main risk period
 
***14 weeks before lambing
 
**The best method of protection is to prevent cats from contaminating the pasture, lambing sheds and feed stores
 
 
 
==[[Protozoa Flashcards - Wikibugs#Tissue Cyst Forming Coccidia|Tissue Cyst Forming Coccidia Flashcards]]==
 

Latest revision as of 23:31, 9 April 2010