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Tissue cyst-forming coccidia (view source)
Revision as of 17:38, 23 November 2008
, 17:38, 23 November 2008no edit summary
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==Neospora==
*2 main species
**''Neospora caninum'' in the dog
**''Neospora hughesi'' in the horse
*Sporulated oocysts measuring just 10μm
*Oocyst contains 2 sporocysts with 4 sporozoites
*Route of transmission not fully understood
*Often misdiagnosed as ''Toxoplasma gondii''
**''Sarcocystis'' cysts have thicker walls
*Infection diagnosed by IFAT, ELISA or PCR
**Identification of lesions and organisms in tissue using immunohistochemical staining
**Eliminate other causes of abortion first
'''Life cycle'''
*Life cycle similar to ''Toxoplasma gondii''
*Limited range of warm-blooded intermediate hosts
**Asexual reproduction occurs in intermediate host forming tissue cysts
*Host range of sexual stage is unknown for ''N.caninum''
**Intermediate host for ''N.hughesi'' is the horse, but the definitive host is unknown
*Final host
**Dogs pass oocysts
**Role not fully understood in pathogenesis
**5 day prepatent period
**Other wild canids may also act as final definitive hosts
*Intermediate host
**Mostly cattle
**Natural infection has been documented in other herbivores
*Transmission
**Transplacental infection occurs in all intermediate hosts and in the canine final host
***Transplacental can occur in '''successive pregnancies'''
**In cattle, vertical transmission occurs
***Post-natal infection occurs but is less common
'''Pathogenesis'''
*Dogs
**Occurs mainly in puppies
**Causes ascending paralysis, especially of hind limbs, with muscle wasting
**Causes sudden collapse due to myocarditis
**More than puppy in a litter may be affected, although this may not occur simultaneously
**Successive litters affected
*Cattle
**Commenest cause of infectious abortion in dairy cattle
**Congenitally infected calves can have encephalomyelitis and paresis
**Abortion usually occurs between 5-7 months of gestation but can occur as early as 3 months
**No other clinical signs in the cow
**Repeat abortions possible in same cow (persistently infected)
*Horses
**Myeloencephalitis
**Transplacental infection occurs
**Disease only diagnosed in USA
*''Neospora caninum'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
'''Prevention and Control'''
*Do not allow dogs access to calving cows, placental membranes and aborted or dead calves
*Do not allow dogs to defecate in cattle feeding areas
*Identify and cull seropositive cattle, or do not breed from them or their progeny
*Select seronegative cattle for breeding
*Vaccinate
**Only in the USA
**Neoguard or Intervet
**Killed protozoal vaccine for healthy, preganant cows
**Dosed in first 3 weeks of pregnancy and then every 3-4 weeks during gestation
**Revaccination with 2 doses during each subsequent pregnancy
==Sarcocystis==
[[Image:Sarcocystis Life Cycle.jpg|thumb|right|150px|''Sarcocytis'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
[[Image:Sarcocystic.jpg|thumb|right|150px|''Sarcocytis'' - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona]]
*Most infections are asymptomatic
*Heavy infections are causes of chronic wasting in large animals, hide sondemnation and downgrading of carcasses
*''Sarcocystis'' should be differentiated from other tissue-cyst forming coccidia
*There are many species of ''Sarcocystis'' which differ in size from microscopic to several centimetres in length
**''S.neurona'' is an important equine pathogen in the USA
*Infective cyst in the intermediate host is called a '''sarcocyst'''
'''Life Cycle'''
*Individual life cycles incompletely misunderstood
*Indirect life cycle
*Life cycle alternates between the final and the obligatory intermediate host
*Only '''one''' final and '''one''' intermediate host
*Sporulated oocyst has 2 sporocysts containing 4 sporozoites
**Naked oocyst usually seen in faeces as the oocyst wall is very delicate
**Oocyst measures 15μm in length
*No schizogony in final host
*Gametogeny occurs deep in subepithelial tissue
*Faecal oocyst count is low
*Oocysts are sporulated when passed
**Difficult to find on faecal examination as the sporocysts are few in number and small
*Ingestion of sporocyst by intermediate host
**2 phases of rapid asexual reproduction in vascular endothelial cells
**Slow multiplication of bradyzoites in muscle tissue
**Sarcocyst forms with bradyzoites inside, surrounded by a cyst wall and divided into compartments
'''Epidemiology'''
*Final hosts are carnivores and omnivores
*Intermediate hosts are herbivores and omnivores
*Humans are the final host for some species and the intermediate hosts for others
**Final host for species infecting cattle and pigs
*Dogs are final hosts for species infecting cattle, sheep, goats, pigs and horses
*Cats are final hosts for species infecting cattle, sheep and pigs
'''Pathogenesis'''
*Widespread infection but mostly asymptomatic
*Cause meat inspection losses
*''Sarcocystis'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
*Experimental infections cause severe, acute pyrrhexic disease when the organism multiplies in the vascular endothelium
*Can cause chronic wasting disease in cattle and horses
**Causes abortion and post-natal disease in sheep
*Equine protozoal myeloencephalitis
**Necrotising encephalomyelitis affecting the grey and white matter of the CNS
**Caused by ''S.neurona''
**Opossum thought to be the definitive host
**Horses thought to be accidental hosts
**Natural intermediate hosts currently unknown
**Western Blotting shows 50% of horses in the USA are seropositive
**Risk factors poorly understood
**Causes spinal cord dysfunction
***Ataxia and paralysis
==Toxoplasma==
==Toxoplasma==
***14 weeks before lambing
***14 weeks before lambing
**The best method of protection is to prevent cats from contaminating the pasture, lambing sheds and feed stores
**The best method of protection is to prevent cats from contaminating the pasture, lambing sheds and feed stores