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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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*Ingestion of sporocyst by intermediate host
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**2 phases of rapid asexual reproduction in vascular endothelial cells
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**Slow multiplication of bradyzoites in muscle tissue
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**Sarcocyst forms with bradyzoites inside, surrounded by a cyst wall and divided into compartments
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'''Epidemiology'''
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*Final hosts are carnivores and omnivores
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*Intermediate hosts are herbivores and omnivores
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*Humans are the final host for some species and the intermediate hosts for others
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**Final host for species infecting cattle and pigs
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*Dogs are final hosts for species infecting cattle, sheep, goats, pigs and horses
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*Cats are final hosts for species infecting cattle, sheep and pigs
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'''Pathogenesis'''
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*Widespread infection but mostly asymptomatic
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*Cause meat inspection losses
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*''Sarcocystis'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
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*Experimental infections cause severe, acute pyrrhexic disease when the organism multiplies in the vascular endothelium
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*Can cause chronic wasting disease in cattle and horses
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**Causes abortion and post-natal disease in sheep
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*Equine protozoal myeloencephalitis
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**Necrotising encephalomyelitis affecting the grey and white matter of the CNS
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**Caused by ''S.neurona''
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**Opossum thought to be the definitive host
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**Horses thought to be accidental hosts
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**Natural intermediate hosts currently unknown
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**Western Blotting shows 50% of horses in the USA are seropositive
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**Risk factors poorly understood
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**Causes spinal cord dysfunction
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***Ataxia and paralysis
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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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