Toxoplasma gondii (1) Flashcards
What are the definitive hosts?
Cats
Other felids
What are the intermediate hosts?
Warm blooded animals
- Include: Humans
Dogs
Livestock
BirdsHow do you identify?
Oocysts found in feces
- Small (12 micro m)
- Sporulated: 1-5 days
- Contain 2 Sporocysts
- Contains 4 sporozoites each
Explain the life cycle
PPP: 3-40 days
Unsporulated Oocysts shed for 1-2 weeks
Oocysts take 1-5 days to Sporulate in environment
- Become infective
IH infected after ingesting Sporulated oocyst
Transform to tachyzoites - localize in neural and muscle tissue
- Develop to tissue cysts containing bradyzoites
Cats infected by consuming infected IH and cysts
Tissue cyst wall digested
Liberated bradyzoites initiate cycle of schizogonous and gametogonous development culminating in production of Oocysts in 3-10 days
Cats also infected by direct ingestion of Sporulated Oocysts and serve as IH
IH can also ingest undercooked meat containing bradyzoites or tachyzoites
Humans infected via several different routes:
- Animal to human - Eating undercooked meat of animals harboring tissue cysts - Consuming contaminated food/water - Blood transfusion/organ transplantation - Transplacentally mother -> fetus
In human host, tissue cysts form (commonly in skeletal muscle, myocardium, brain, and eyes)
- Remain throughout life of host
What are the sites of infection?
Intestinal and extraintestinal tissues
- Muscle, liver, lung, brain, etc.
Gametogony only in definitive hosts
Describe the Pathogenesis
Asymptomatic
Clinical signs depend on organ/extent of injury
Death of intestinal/extraintestinal cells due to tachyzoites
Clinical disease can occur in cats
- Acute toxoplasmosis
- Disseminated infection
- Most lesions in liver, lungs, spleen, pancreas, eyes, lymph
nodes
- Severe signs seen in cats with FIV
- Pneumonia
Cats develop immunity after initial infection - shed only once in lifetime
Sheep and Goats
- Aborted fetuses may not have gross significant lesions
- Placenta has characteristic lesions:
- Cotyledons
- Bright red
- Numerous white flecks or small white nodules (2.0
mm)
- Heavy infections
- Tachyzoites produce areas of necrosis in vital organs,
myocardium, lungs, liver, brain
How do you diagnose?
Oocysts in cat feces - fecal examination
- Oocysts very small
- Shed for 1-2 week period
Serological tests
Demonstration of organisms in tissues
Modified direct agglutination test
ELISA
IFA tests
Latex and indirect hemogluttination - poor
IgM ELISA useful in diagnosing acute toxoplasmosis in cats
Important cause of abortion in ewes (prenatal mortality in sheep/goats)
Calves susceptible
- Still born seen - Must be differentiated from those infected with
Neospora caninum (immunohistochemical or
molecular methods)
Tachyzoites difficult to find
- Present in brain and placenta
Cysts observed in stained biopsy specimens
Diagnosis of congenital infections via detecting T. gondii DNA in amniotic fluid via molecular methods (PCR)
How do you treat and prevent?
Pregnant women avoid contact with sources of Oocysts
Wash vegetables and fruit
Humans should avoid contact with feces/eating undercooked meat with infected tissue cysts
Exposure of human feces
- Results of exposure of nonimmune mother to T. gondii infection
during pregnancy
- Hazard of death
- Congenital malformation
- Loss of vision
- Mental retardation
Can cause damage to:
- Brain - Eyes - Muscle - Liver - Lungs
Women with circulating antibody need not worry about exposing unborn child to congenital toxoplasmosis
No vaccine approved
Treated with nonsulfonamides and sulfonamides
Live vaccine for sheep consists of tachyzoites given 3 weeks before tupping (mating with ram)
- Not available in USA
What is important about Toxoplasma gondii?
It is ZOONOTIC
