Toxoplasmosis and its Impact on the Nervous System Flashcards
What is Toxoplasma gondii?
Infects multiple Intermediate hosts (warm-blooded mammals)
* Cat → Definitive host through oocysts in faeces
* Infection is common but often benign
* In epithelial cells of small intestine of cat
Stage of T. gondii - Tachyzoite
Appearance - crescent-shaped, pointed anterior & rounded posterior
Function - divides asexually
Stage of T. gondii - Bradyzoite
Appearance - Spherical cyst that is more prevalent in the nerves + muscles
Function - Cyst cell wall can be destroyed by pepsin or trypsin but is resistant to gastric juices
Stage of T. gondii - Sporozoites
- Infects epithelial cells
- Converts to tachyzoites
Hosts of T. gondii
Cat faeces
- Intermediate host (unwashed veg or undercooked meat)
- Environmental e.g in the soil
- Blood transfusion/organ transplant
Transplacental
Tranmission of T.gondii - Congenital
- Mother to offspring
- Tachyzoites through placenta or milk
Tranmission of T.gondii - Organ Transplant
e.g. heart, kidney, liver, bone marrow
Tranmission of T.gondii - Faecal-oral
Through cat feces (oocysts)
Tranmission of T.gondii - Carnivorism
- Undercooked meat results in bradyzoite survival after cyst wall is degraded by enzymes
- Also can happen with unpasteurised milk
Most to least common meats that T. gondii cysts are found
- Highest : pigs, sheep, goats
- Then: free-range poultry, pigeons, farm deer, game animals, dogs
- Then: horses + commercially raised poultry
- Least : Buffaloes, cattle
T. gondii is a zoonotic disease in cats - Symptoms + means of infection
- Symptoms: fever, ocular inflammation, anorexia, lethargy, neurological abnormalities
- Cats shed oocysts after ingesting tissue cysts more often than with tachyzoites or oocyst
- 1 bradyzoite ingested infection = ~1000 oocysts
Stages of asexual development in intermediate host
- Tachyzoites (endogeny) in many
host cell types & some form cysts - Bradyzoites (slow endogeny) in
cysts in neural & muscular tissue
(terminal stage)
T. gondii’s prevalence in humans
- Differs from geographical areas - the more meat eaten, the higher the prevalance
- Sabin-Feldman dye test- gold standard (labour
intensive, need live parasites) - Many antibody tests are now available
Methods of prevention from zoonotic transmission
- Washing hands, fruit + veg
- Only drink treated water
- Wear gloves when gardening
- Clean litter tray to prevent accumulation
T. gondii’s effects in humans
- Most cases are asymptomatic
- Lymphadenopathy, encephalitis, sepsis syndrome, myocarditis,
hepatitis - Infection prior to 4-6 months before conception may infer protective
immunity EXCEPT in immunocompromised women e.g. AIDs
Ocular Toxoplasmosis
- 0.4/100 000/year in British-born patients
- Symptoms 20-40 years old
- Most common symptom (28-50%)- chorioretinitis (inflamed choroid)
- White wisp appearance
- Recurrent(2/3 symptomatic infections
How toxoplasmosis affects the nervous system
- Enters endothelial cells
- Then enters neuron as a cyst]
- Reactivation suppression
- Increases excitatory + decreases inhibitory neurotransmitters
- Leads to seizures
Results of toxoplasmosis in the nervous system
- Reduced mental/physical wellbeing in 2
months following infection - Risk of suicidal behaviour increased
- Concentration reduced
- Chronic infection - risk of schizophrenia, bipolar
disorder, addiction, OCD
Reason for mental issues from chronic infection - Immune response
- PAMPs (profilin)
- Chronic immune
response can cause brain inflammation
Reason for mental issues from chronic infection - Cyst location
- In dendritic spines could reduce neuron function
- Reduction in function could be linked to schizophrenia
Reason for mental issues from chronic infection - Neurotransmitter change
- Reduction of dopamine + increase in norepinephrine &
serotonin - In mice - competitive
binding for dopamine could lead to behaviour change - May damage dendritic spine
