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| + | #REDIRECT[[:Category:Tissue Cyst Forming Coccidia]] |
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| − | {{toplink
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| − | |backcolour =
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| − | |linkpage =Parasites
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| − | |linktext =PARASITES
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| − | |pagetype=Bugs
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| − | |sublink1=Protozoa
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| − | |subtext1=PROTOZOA
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| − | }}
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| − | <br>
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| − | ==Toxoplasma==
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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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| − | *1 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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| − | **Reffered to as '''facultatively heterxenous'''
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| − | **Intermediate host is not essential for completion of the life cycle
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| − | *Gametogeny (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'' as a prepatent period of 3 weeks
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| − | **Or eat the tissues of an infective intermediate host where ''Toxoplasma gondii'' as a prepatent period of 3-10 days
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| − | **Self-limiting infection
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| − | **Oocysts shed for 1-2 weeks
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| − | ***Shedding can occur later if immunity wanes or cat is immunocompromised
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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 or 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 '''endogeny''' (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 an immunity in 2 weeks when 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 particulary 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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| − | **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 resorbtion
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| − | **Infection during the second trimester leads to fetal 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 aquired 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 be caused by even 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 innoculation 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 (will hunt!)
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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 eating 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 when pregnant
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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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| − | ==Sarcocystis==
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| − | [[Image:Sarcocystis Life Cycle.jpg|thumb|right|150px|''Sarcocytis'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
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| − | [[Image:Sarcocystic.jpg|thumb|right|150px|''Sarcocytis'' - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
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| − | *Most infections are asymptomatic
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| − | *Heavy infections are causes of chronic wasting in large animals, hide sondemnation and downgrading of carcasses
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| − | *''Sarcocystis'' should be differentiated from other tissue-cyst forming coccidia
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| − | *There are many species of ''Sarcocystis'' which differ in size from microscopic to several centimetres in length
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| − | **''S.neurona'' is an important equine pathogen in the USA
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| − | *Infective cyst in the intermediate host is called a '''sarcocyst'''
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| − | '''Life Cycle'''
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| − | *Individual life cycles incompletely misunderstood
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| − | *Indirect life cycle
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| − | *Life cycle alternates between the final and the obligatory intermediate host
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| − | *Only '''one''' final and '''one''' intermediate host
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| − | *Sporulated oocyst has 2 sporocysts containing 4 sporozoites
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| − | **Naked oocyst usually seen in faeces as the oocyst wall is very delicate
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| − | **Oocyst measures 15μm in length
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| − | *No schizogony in final host
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| − | *Gametogeny occurs deep in subepithelial tissue
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| − | *Faecal oocyst count is low
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| − | *Oocysts are sporulated when passed
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| − | **Difficult to find on faecal examination as the sporocysts are few in number and small
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| − | '''Pathogenesis'''
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| − | *Cause meat inspection losses
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| − | *''Sarcocystis'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
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| − | ==Neospora==
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| − | *2 main species
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| − | **''Neospora caninum'' in the dog
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| − | **''Neospora hughesi'' in the horse
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| − | *Sporulated oocysts measuring just 10μm
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| − | *Oocyst contains 2 sporocysts with 4 sporozoites
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| − | *Route of transmission not fully understood
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| − | *Often misdiagnosed as ''Toxoplasma gondii''
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| − | **''Sarcocystis'' cysts have thicker walls
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| − | *Infection diagnosed by IFAT, ELISA or PCR
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| − | **Identification of lesions and organisms in tissue using immunohistochemical staining
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| − | **Eliminate other causes of abortion first
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| − | '''Life cycle'''
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| − | *Life cycle similar to ''Toxoplasma gondii''
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| − | *Limited range of warm-blooded intermediate hosts
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| − | **Asexual reproduction occurs in intermediate host forming tissue cysts
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| − | *Host range of sexual stage is unknown for ''N.caninum''
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| − | **Intermediate host for ''N.hughesi'' is the horse, but the definitive host is unknown
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| − | *Final host
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| − | **Dogs pass oocysts
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| − | **Role not fully understood in pathogenesis
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| − | **5 day prepatent period
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| − | **Other wild canids may also act as final definitive hosts
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| − | *Intermediate host
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| − | **Mostly cattle
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| − | **Natural infection has been documented in other herbivores
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| − | *Transmission
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| − | **Transplacental infection occurs in all intermediate hosts and in the canine final host
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| − | ***Transplacental can occur in '''successive pregnancies'''
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| − | **In cattle, vertical transmission occurs
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| − | ***Post-natal infection occurs but is less common
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| − | '''Pathogenesis'''
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| − | *Dogs
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| − | **Occurs mainly in puppies
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| − | **Causes ascending paralysis, especially of hind limbs, with muscle wasting
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| − | **Causes sudden collapse due to myocarditis
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| − | **More than puppy in a litter may be affected, although this may not occur simultaneously
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| − | **Successive litters affected
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| − | *Cattle
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| − | **Commenest cause of infectious abortion in dairy cattle
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| − | **Congenitally infected calves can have encephalomyelitis and paresis
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| − | **Abortion usually occurs between 5-7 months of gestation but can occur as early as 3 months
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| − | **No other clinical signs in the cow
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| − | **Repeat abortions possible in same cow (persistently infected)
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| − | *Horses
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| − | **Myeloencephalitis
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| − | **Transplacental infection occurs
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| − | **Disease only diagnosed in USA
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| − | *''Neospora caninum'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
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| − | '''Prevention and Control'''
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| − | *Do not allow dogs access to calving cows, placental membranes and aborted or dead calves
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| − | *Do not allow dogs to defecate in cattle feeding areas
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| − | *Identify and cull seropositive cattle, or do not breed from them or their progeny
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| − | *Select seronegative cattle for breeding
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| − | *Vaccinate
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| − | **Only in the USA
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| − | **Neoguard or Intervet
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| − | **Killed protozoal vaccine for healthy, preganant cows
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| − | **Dosed in first 3 weeks of pregnancy and then every 3-4 weeks during gestation
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| − | **Revaccination with 2 doses during each subsequent pregnancy
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