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Tissue cyst-forming coccidia (view source)
Revision as of 10:54, 7 January 2009
, 10:54, 7 January 2009no edit summary
*Transmission
*Transmission
**Transplacental infection occurs in all intermediate hosts and in the canine final host
**Transplacental infection occurs in all intermediate hosts and in the canine final host
***Transplacental can occur in '''successive pregnancies'''
***Transplacental transmission can occur in '''successive pregnancies'''
**In cattle, vertical transmission occurs
**In cattle, vertical transmission occurs
***Post-natal infection occurs but is less common
***Post-natal infection occurs but is less common
**Causes ascending paralysis, especially of hind limbs, with muscle wasting
**Causes ascending paralysis, especially of hind limbs, with muscle wasting
**Causes sudden collapse due to myocarditis
**Causes sudden collapse due to myocarditis
**More than puppy in a litter may be affected, although this may not occur simultaneously
**More than 1 puppy in a litter may be affected, although this may not occur simultaneously
**Successive litters affected
**Successive litters affected
*Cattle
*Cattle
**Commenest cause of infectious abortion in dairy cattle
**Commonest cause of infectious abortion in dairy cattle
**Congenitally infected calves can have encephalomyelitis and paresis
**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
**Abortion usually occurs between 5-7 months of gestation but can occur as early as 3 months
**Only in the USA
**Only in the USA
**Neoguard or Intervet
**Neoguard or Intervet
**Killed protozoal vaccine for healthy, preganant cows
**Killed protozoal vaccine for healthy, pregnant cows
**Dosed in first 3 weeks of pregnancy and then every 3-4 weeks during gestation
**Dosed in first 3 weeks of pregnancy and then every 3-4 weeks during gestation
**Revaccination with 2 doses during each subsequent pregnancy
**Revaccination with 2 doses during each subsequent pregnancy
*Most infections are asymptomatic
*Most infections are asymptomatic
*Heavy infections are causes of chronic wasting in large animals, hide sondemnation and downgrading of carcasses
*Heavy infections are causes of chronic wasting in large animals, hide condemnation and downgrading of carcasses
*''Sarcocystis'' should be differentiated from other tissue-cyst forming coccidia
*''Sarcocystis'' should be differentiated from other tissue-cyst forming coccidia
'''Life Cycle'''
'''Life Cycle'''
*Individual life cycles incompletely misunderstood
*The individual life cycle of some species is incompletely understood
*Indirect life cycle
*Indirect life cycle
*Sporulated oocyst has 2 sporocysts containing 4 sporozoites
*Sporulated oocyst has 2 sporocysts containing 4 sporozoites
**Naked oocyst usually seen in faeces as the oocyst wall is very delicate
**Naked sporocyst usually seen in faeces as the oocyst wall is very delicate
**Oocyst measures 15μm in length
**Oocyst measures 15μm in length
*''Sarcocystis'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
*''Sarcocystis'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
*Experimental infections cause severe, acute pyrrhexic disease when the organism multiplies in the vascular endothelium
*Experimental infections cause severe, acute pyrexic disease when the organism multiplies in the vascular endothelium
*Can cause chronic wasting disease in cattle and horses
*Can cause chronic wasting disease in cattle and horses
[[Image:Toxoplasma Life Cycle.jpg|thumb|right|150px|''Toxoplasma'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
[[Image:Toxoplasma Life Cycle.jpg|thumb|right|150px|''Toxoplasma'' Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC]]
[[Image:Toxoplasma gondii 2.jpg|thumb|right|150px|''Toxoplasma gondii'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]
[[Image:Toxoplasma gondii 2.jpg|thumb|right|150px|''Toxoplasma gondii'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]
*1 major pathogenic species called ''Toxoplasma gondii''
*Major pathogenic species called ''Toxoplasma gondii''
*Causes disease in a wide range of animal species including humans
*Causes disease in a wide range of animal species including humans
*Usually indirect
*Usually indirect
**Reffered to as '''facultatively heterxenous'''
**Referred to as '''facultatively heteroxenous'''
**Intermediate host is not essential for completion of the life cycle
**Intermediate host is not essential for completion of the life cycle
*Gametogeny (sexual stage) is host specific for felids
*Gametogony (sexual stage) is host specific for felids
*Any warm blooded animal can act as a facultative intermediate host
*Any warm blooded animal can act as a facultative intermediate host
*Cats
*Cats
**Sporulation occurs in 2-3 days
**Sporulation occurs in 2-3 days
**Cats either swallow infective (sporulated) oocysts where ''Toxoplasma gondii'' as a prepatent period of 3 weeks
**Cats either swallow infective (sporulated) oocysts where ''Toxoplasma gondii'' has 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
**Or eat the tissues of an infected intermediate host where ''Toxoplasma gondii'' has a prepatent period of 3-10 days
**Self-limiting infection
**Self-limiting infection
**Oocysts shed for 1-2 weeks
**Oocysts are shed for 1-2 weeks
***Shedding can occur later if immunity wanes or cat is immunocompromised
***Shedding can occur later if immunity wanes or cat is immuno-compromised
*Intermediate host
*Intermediate host
**3 sources of infection
**3 sources of infection
***Oocysts from environment contaminated by cat faeces
***Oocysts from environment contaminated by cat faeces
***Eating cysts in tissues or other infected hosts through carnivorism or undercooked meat
***Eating cysts in tissues of other infected hosts through carnivorism or undercooked meat
***Transplacental transmission in some host species during the acute phase of infection
***Transplacental transmission in some host species during the acute phase of infection
*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
**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'''
***Parasite enters cell and asexual reproduction occurs by '''endodyogeny''' (budding) producing 8-16 '''tachyzoites'''
***Tachyzoites are released when host cell bursts
***Tachyzoites are released when host cell bursts
***Haematogenous spread as more cells are infected
***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
***Infection continues until the animal develops immunity (around 2 weeks) at which point the infection enters the chronic phase
*Chronic phase of infection
*Chronic phase of infection
***Groups of slow growing intracellular '''bradyzoites''' become walled off forming infective '''cysts'''
***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
***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
***Cysts remain viable for months to years and are particularly numerous in muscle and nervous tissue
***If immunity is suppressed the infection can revert to the acute form
***If immunity is suppressed the infection can revert to the acute form
*Sheep
*Sheep
**Mostly asymptomatic
**Mostly asymptomatic
**If a non-immune ewe is infected during pregnancy the consequences will be serious
**However, 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 first trimester leads to resorption
**Infection during the second trimester leads to fetal death and mummification
**Infection during the second trimester leads to foetal death and mummification
**Infection during the last trimester leads to a weak or stillborn lamb
**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
**Aborted ewes show focal necrotic placentitis with white lesions in the cotyledons and foetal tissue
*Clinical outbreaks of toxoplasmosis are '''sporadic'''
*Clinical outbreaks of toxoplasmosis are '''sporadic'''
**Immunity is aquired before tupping
**Immunity is acquired before tupping
**Significant ill-effects are unlikely if immune ewes are infected during pregnancy
**Significant ill-effects are unlikely if immune ewes are infected during pregnancy
**Not shed from sheep to sheep so predicting outbreaks is difficult
**Not shed from sheep to sheep so predicting outbreaks is difficult
**Mostly asymptomatic
**Mostly asymptomatic
**Virulent strains cause flu-like symptoms, malaise and/or lymphadenopathy
**Virulent strains cause flu-like symptoms, malaise and/or lymphadenopathy
**In immunodeficient patients, disease can be caused by even avirulent strains
**In immunodeficient patients, disease can even be caused by avirulent strains
**If a non-immune women is infected during pregnancy, abortion or the birth of a congenitally infected child can result
**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
***E.g. Hydrocephalus, opthalmitis, mental retardation
**Sabin-Feldman Dye test (old method)
**Sabin-Feldman Dye test (old method)
**ELISA
**ELISA
**Mouse innoculation for confirmation
**Mouse inoculation for confirmation
*Cat
*Cat
'''Prevention'''
'''Prevention'''
*Cat
*Cat
**Impossible if cat is allowed outdoors (will hunt!)
**Impossible if cat is allowed outdoors due to hunting
**If kept indoors, only canned food should be fed and vermin controlled
**If kept indoors, only canned food should be fed and vermin controlled
**ELISA to check if seropositive
**ELISA to check if seropositive
**Avoid ingestion of tissue cysts
**Avoid ingestion of tissue cysts
***Do not eat undercooked meat
***Do not eat undercooked meat
***Wash hands after eating raw meat
***Wash hands after handling raw meat
***Take care when lambing or dealing with sheep abortions and stillbirths
***Take care when lambing or dealing with sheep abortions and stillbirths
***Pregnant women should avoid lambing altogether when pregnant
***Pregnant women should avoid lambing altogether
*Sheep
*Sheep