Difference between revisions of "Tissue cyst-forming coccidia"

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

Latest revision as of 23:31, 9 April 2010