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