Toxoplasma gondii

Question 1

Toxoplasma gondii

Answer 1

• protozoan, apiocomplexan (often refered to as a coccidian)
• infects most species of warm-blooded animals (obligate-intracellular lifecycle; invades host cells and evades the immune system)
• sexually multiply in cats

Question 2

Describe the morphology of Toxoplasma gondii

Answer 2

• 2 forms/stages that are both extraintestinal
• Trophozoite form: 2 generations that include tachyzoites (fast multiplying) and bradyzoites (slow multiplying/ inert)
  The trophozoites are crescentic and have 1 nucleus and asexually reproduce via endodygeny
• Cyst form: resting/chronic form where it has a thick wall that protects it from the immune system, digestive enzymes, and inflammation. This is the result of asexual multiplication

Question 3

Describe the sexual reproduction of Toxoplasma gondii.

Answer 3

There is an intestinal form, oocyst, that is only in cats. The oocyst is 2 sporocysts containing 4 sporozoites each with a flexible wall (sexual cycle that occurs in the cats jejunal epithelium)

Question 4

Describe the pathogenesis of Toxoplasmosis.

Answer 4

• Parasite infects both phogocytic and non-phagocytic nucleated cells (does not infect RBCs)
• Cell invasion facilitated by apical complex/ drill-like conoid, micronemes, rhoptries, and dense granules
• survival assured by creation of protective paraphophoruous vacuole inside of the host cell

Question 5

Describe the acute and chronic phases of toxoplasmosis.

Answer 5

Early (acute) phase: tachyzoites invading cells, cell destruction/ necrosis, mononuclear cell inflammation, blood vessel blockage

Late (chronic) phase: brabyzoites/ tissue cysts, latency/immunological evasion, and hypersensitivity

Question 6

Describe the life cycle of Toxoplasma?

Answer 6

1. Mouse gets infected with toxoplasma oocyst and the parasite infcts the mouse tissue.
2. The cat eats the mouse and becomes infected with toxoplasma and the sexual cycle of toxoplasmosis occurs here
3. A human host (or other resovoir host) can transmit the parasite from undercooked/ raw meat or from coming in contact with cat feces
4. The tachyzoites infect the liver cells via the bloodstream where the asexual replication occurs (the tachyzoites infect the macrophage or other nucleated cells and distribute the tachyzoites throughout the body)
5. Psudocysts are produced in response to aquired immunity
   Toxomplasmosis does not have a long term effect in humans unless the eyes are infected (blindness) and the cycle tyically revolves around cats.

Question 7

What are the sites of invasion for Toxoplasmosis?

Answer 7

Lymph nodes, cardiac/skeletal muscles, brain, and eyes

Question 8

How does Toxoplasmosis affect the brain? Give some examples.

Answer 8

It can infect the neurons directly, one of the hypotheses is by increasing dopamine synthesis/ release or influencing neurotransmitter metabolism

Examples: increase aggresstion in females, increased impulsivity in males, increased promiscuity in females and males. There is correlation with homicide rates, suiside rates, traffic accidents, and schizophrenia.

Question 9

Describe the clinical prsentation of toxoplasmosis.

Answer 9

Acute: 90% of cases are asymptomatic, ifsymptoms are present they include lymphadenopathy, infectious mononucleosis, jaundice, splenomegly, a rash, and rarely involvment with the nervous system and eye

Chronic 100% asymptomatic

Question 10

Describe the congenital disease of toxoplasmosis?

Answer 10

• transplacental transmission from acute toxoplasmosis during pregnancy
• Can result in spontaneous abortion/ still birth, CSN leisons which can lead to developmental abnormalities (hydrocephalpy, CSF accumulation in the brain; or cerebral calcifications), and can cause blindness if eyes are involve

Potencial for giving birth to a healthy baby and later in life the baby can go blind at a young age

Question 11

What are the rsiks of getting acute toxoplasmosis while pregnant?

Answer 11

1st trimester: 5% risk of congenital infection but a 60% chance of seeing clinical signs in offspring

3rd trimester: 70% risk of congenital infection and 10% chance of seeing clinical signs in offspring

Second timester is in the middle.

Question 12

How is Toxoplasma transmitted?

Answer 12

• ingestion of contaminated meat (that is not cooked fully)
• ingestion/ inhalation of oocyst from cat
• Transfusion/ transplantation
• Transplacentally

Question 13

How is Toxoplamsa diagnosed in the lab?

Answer 13

• Direct: giesma or flourescent antibody stains. NAAT testing, PCR on tissue samples, or animal innoculation (rarely used)
• Serology: Sabin Feldmen dye test, IFA,and EIA