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Tissue cyst-forming coccidia (view source)
Revision as of 12:18, 17 November 2008
, 12:18, 17 November 2008no edit summary
**Intermediate host swallows sporulated oocysts or tissue cysts
**Intermediate host swallows sporulated oocysts or tissue cysts
**Can be transferred between intermediate hosts by carnivorism
**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'''
'''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 can cause [[Pancreas Inflammatory - Pathology#Acute haemorrhagic pancreatitis|acute interstitial pancreatitis]] in systemic toxoplasmosis
*''T. gondii'' in [[Respiratory Parasitic Infections - Pathology#Toxoplasmosis|pneumonia]]
*''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
*''Toxoplasma gondii'' causes [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
*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==
==Sarcocystis==
*Only one final and one intermediate host
*Only one final and one intermediate host
'''Pathogenesis'''
*''Sarcocystis'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
==Neospora==
==Neospora==
**Transplacental infection occurs
**Transplacental infection occurs
**Disease only diagnosed in USA
**Disease only diagnosed in USA
*''Neospora caninum'' in [[Muscles Inflammatory - Pathology#Protozoa|myositis]]
'''Prevention and Control'''
'''Prevention and Control'''