View source for Tissue cyst-forming coccidia

{{unfinished}}

{{toplink
|backcolour =
|linkpage =Parasites
|linktext =PARASITES
|pagetype=Bugs
|sublink1=Protozoa
|subtext1=PROTOZOA
}}
<br>

==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

*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

==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