Difference between revisions of "Tissue cyst-forming coccidia"

From WikiVet English
Jump to navigation Jump to search
(5 intermediate revisions by 2 users not shown)
Line 1: Line 1:
−
#REDIRECT[[:Category:Tissue Cyst Forming Coccidia]]
+
{{review}}
 +
 
 +
{{toplink
 +
|backcolour =
 +
|linkpage =Parasites
 +
|linktext =PARASITES
 +
|pagetype=Bugs
 +
|sublink1=Protozoa
 +
|subtext1=PROTOZOA
 +
}}
 +
<br>
 +
 
 +
==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 transmission 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 1 puppy in a litter may be affected, although this may not occur simultaneously
 +
**Successive litters affected
 +
 
 +
*Cattle
 +
**Commonest 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, pregnant 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]]
 +
[[Image:Sarcocystis in sheep oesophagus.jpg|thumb|right|150px|''Sarcocystis'' in sheep oesophagus - Adam Cuerden]]
 +
[[Image:Equine protozoal myeloencephalitis.jpg|thumb|right|150px|Equine protozoal myeloencephalitis - Wikimedia Commons]]
 +
[[Image:Sarcocystis cruzi.jpg|thumb|right|150px|''Sarcocystis cruzi'' - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine]]
 +
*Most infections are asymptomatic
 +
 
 +
*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
 +
 
 +
*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'''
 +
*The individual life cycle of some species is incompletely understood
 +
 
 +
*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 sporocyst 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 pyrexic 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==
 +
[[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|Protozoa Flashcards]]==

Revision as of 15:41, 7 January 2009

 This article has been peer reviewed but is awaiting expert review. If you would like to help with this, please see more information about expert reviewing.


Infectious agents and parasitesWikiBugs Banner.png
PARASITES
PROTOZOA



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 transmission 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 1 puppy in a litter may be affected, although this may not occur simultaneously
    • Successive litters affected
  • Cattle
    • Commonest 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

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, pregnant 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

Sarcocytis Life Cycle Diagram - Dennis Jacobs & Mark Fox RVC
Sarcocytis - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona
Sarcocystis in sheep oesophagus - Adam Cuerden
Equine protozoal myeloencephalitis - Wikimedia Commons
Sarcocystis cruzi - Courtesy of the Laboratory of Parasitology, University of Pennsylvania School of Veterinary Medicine
  • Most infections are asymptomatic
  • 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
  • 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

  • The individual life cycle of some species is incompletely understood
  • 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 sporocyst 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
  • Experimental infections cause severe, acute pyrexic 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 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

Protozoa Flashcards

Retrieved from "https://en.wikivet.net/index.php?title=Tissue_cyst-forming_coccidia&oldid=42570"