Difference between revisions of "Tissue cyst-forming coccidia"

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#REDIRECT[[:Category:Tissue Cyst Forming Coccidia]]
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[[Neospora]]
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 +
 
 +
[[Sarcocystis]]
 +
 
 +
 
 +
==Toxoplasma==
 +
[[Image:Toxoplasma gondii.jpg|thumb|right|150px|''Toxoplasma gondii'' - Ke Hu and John Murray]]
 +
[[Image:Toxoplasma sporulated oocyst.jpg|thumb|right|150px|''Toxoplasma'' Sporulated Oocyst - Wikimedia Commons]]
 +
[[Image:Toxoplasma Tacchyzoites.jpg|thumb|right|150px|''Toxoplasma'' Tacchyzoites - Wikimedia Commons]]
 +
[[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]]
 +
*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
 +
**Referred to as '''facultatively heteroxenous'''
 +
**Intermediate host is not essential for completion of the life cycle
 +
 
 +
*Gametogony (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'' has a prepatent period of 3 weeks
 +
**Or eat the tissues of an infected intermediate host where ''Toxoplasma gondii'' has a prepatent period of 3-10 days
 +
**Self-limiting infection
 +
**Oocysts are shed for 1-2 weeks
 +
***Shedding can occur later if immunity wanes or cat is immuno-compromised
 +
 
 +
*Intermediate host
 +
**3 sources of infection
 +
***Oocysts from environment contaminated by cat faeces
 +
***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
 +
 
 +
*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 '''endodyogeny''' (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 immunity (around 2 weeks) at which point 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 particularly 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
 +
**However, if a non-immune ewe is infected during pregnancy the consequences will be serious
 +
***Infection during the first trimester leads to resorption
 +
**Infection during the second trimester leads to foetal 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 acquired 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 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
 +
***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 inoculation 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 due to hunting
 +
**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 handling raw meat
 +
***Take care when lambing or dealing with sheep abortions and stillbirths
 +
***Pregnant women should avoid lambing altogether
 +
 
 +
*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
 +
 
 +
==[[Protozoa Flashcards - Wikibugs#Tissue Cyst Forming Coccidia|Tissue Cyst Forming Coccidia Flashcards]]==

Revision as of 22:59, 9 April 2010

Neospora


Sarcocystis


Toxoplasma

Toxoplasma gondii - Ke Hu and John Murray
Toxoplasma Sporulated Oocyst - Wikimedia Commons
Toxoplasma Tacchyzoites - Wikimedia Commons
Toxoplasma Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC
Toxoplasma gondii - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine
  • 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
    • Referred to as facultatively heteroxenous
    • Intermediate host is not essential for completion of the life cycle
  • Gametogony (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 has a prepatent period of 3 weeks
    • Or eat the tissues of an infected intermediate host where Toxoplasma gondii has a prepatent period of 3-10 days
    • Self-limiting infection
    • Oocysts are shed for 1-2 weeks
      • Shedding can occur later if immunity wanes or cat is immuno-compromised
  • Intermediate host
    • 3 sources of infection
      • Oocysts from environment contaminated by cat faeces
      • 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
  • 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 endodyogeny (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 immunity (around 2 weeks) at which point 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 particularly 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
    • However, if a non-immune ewe is infected during pregnancy the consequences will be serious
      • Infection during the first trimester leads to resorption
    • Infection during the second trimester leads to foetal 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 acquired 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 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
      • E.g. Hydrocephalus, opthalmitis, mental retardation
  • Dogs
    • Complication of canine distemper
    • Causes pneumonia and encephalitis
  • Cattle and horses
    • Sometimes infectious causing opthalmitis

Epidemiology

  • Serology
    • Sabin-Feldman Dye test (old method)
    • ELISA
    • Mouse inoculation 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 due to hunting
    • 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 handling raw meat
      • Take care when lambing or dealing with sheep abortions and stillbirths
      • Pregnant women should avoid lambing altogether
  • 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

Tissue Cyst Forming Coccidia Flashcards