Toxoplasmose Flashcards
What is the pathogen responsible for Toxoplasmosis
Toxoplasma gondii
What is the global distribution of Toxoplasmosis?
World wide distribution
What is the definitive host of Toxoplasma
The cat. About 1% of housecats
What is the intermediate host of Toxoplasma
Other mammals and birds can act as carries without the parasite reaching maturity
What is the incubation period of Toxoplasmosis
5 to 21 days
What are the several transmission routes
- Mother to fetus (transplacental)
- Ingestion of oocytes, undercooked infected milk, or contaminated milk or water
- Inhalation of sporulated oocysts
- Transportation/transfusion
Describe the life cycle of Toxoplasmosis
1- Both oocyst and tissue cysts transform into trachyzoites shortly after ingestion.
2- Trachyzoites localized in neural and mussel tissue and develop into tissue cyst bradyzoites.
3- Cats become infected after consuming intermediate hosts harboring tissue cysts or ingestion of sporulated oocysts.
4- Animals bred for human consumption and wild game may also become infected with tissue cysts after ingestion of sporulated oocysts in the environment.
How a pregnant woman can infect the fetus
If a pregnant woman becomes infected, tachyzoites can infect the fetus via the bloodstream.
What is a tachyzoite
It’s the infective invasive trophozoite with a crescent shape (banana shape)
What is bradyzoite
The latent stage (cyst form) consists of large 10-100 um pseudocysts filled with trophozoites (crescent-shaped)
What is oocyst
Only present in cat feces. The cyst structure contains two sporocysts, each with 4 sporozoites inside
How does the replication occur in Toxoplasma gondii
By binary fission
Where do the tachyzoites multiply
They invade multiple host cells, including:
- Muscle cells
- Nerve cells
- Epithelial cells
- Macrophages
Describe Tachyzoite replication in cats
Tachyzoites replicate in various host cells, including intestinal epithelial cells. They can form oocysts and be released in cat feces (definitive host)
Describe Tachyzoite replication in Human
- Tachyzoites replicate in humans in various cells, including muscles and neurons.
- This replication can lead to acute infection but does not produce oocysts. A human can remain infected without transferring the infection to others.
Describe pathogenesis in Normal host
In healthy individuals, both humoral (antibody-mediated) and cellular (T-cell-mediated) immune responses work together to limit infection and its spread throughout the body.
Describe pathogenesis in Immunocompromised
There is a great risk of the disease reactivating, which can lead to more severe diseases like necrotizing lesions in vital organs (heart, brain, lungs).
Describe pathogenesis in mice
Toxoplasmosis studies in mice give more insights into the mechanisms of infection and host defense
What are the clinical manifestations observed
1- Congenital disease
2- Acquired disease
3- Immunocompromized
4- Ocular
Describe congenital disease
- 40% of infants are infected at birth if mom is infected during pregnancy, with 10% severe
- The risk of infection increases with gestational age (GA), but the impact on the fetus decreases with GA
- Symptoms may not appear at birth and might develop later.
- Classic symptoms: retinitis, cerebral calcification, hydrocephalus, mental retardation
Describe acquired disease
- 90% are asymptomatic
- Generally self-resolves
- Among symptomatic, cases are divided into:
1- Lymphadenitis: most common manifestation, affection cervical lymph nodes
2- Typhus-like syndrome: this is usually presented with a combination of (rash, cardiac symptoms, neurological symptoms, and pneumonia)
3- CNS involvement: fatal
4- Retinochroiditis: second most common symptoms
Describe immunocompromized primary sites infection of toxoplasmosis disease
- Reaction of latent or new acquisition
- Primary infection sites: CNS, mass lesion (tumor-like growth or accesses), encephalopathy, meningoencephalitis
- Multiple organ complications: lungs, GI, pancreas, skin, eyes, heart, liver
Describe ocular
- T. gondii causes 35% of chorioretinitis
Cause: primarily congenital, some are acquired, AIDS
Symptoms: blurred vision, scotomas, photophobia, eye pain.
Impact on vision: macular involvement with loss of central vision, extraocular muscle involvement
Describe the general diagnosis
- Serology is the standard method.
- Congenital infection: Diagnosed by IgM or persistently high IgG.
- Ocular toxoplasmosis: Typical lesions + IgG.
- Immunocompetent individuals: Usually asymptomatic or present with lymphadenitis.
- Serologic tests:
IgG: Sabin-Feldman dye test, IFA, ELISA.
IgM: ELISA, immunosorbent assays.
