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| − | ==Toxoplasma==
| + | [[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]] | |
| − | [[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
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| | ==[[Protozoa Flashcards - Wikibugs#Tissue Cyst Forming Coccidia|Tissue Cyst Forming Coccidia Flashcards]]== | | ==[[Protozoa Flashcards - Wikibugs#Tissue Cyst Forming Coccidia|Tissue Cyst Forming Coccidia Flashcards]]== |