Toxoplasmosis Overview

Toxoplasmosis Overview

• Toxoplasma gondii is an intracellular coccidian protozoan
• The resulting illness is called toxoplasmosis

Common Infection Routes

• Oral ingestion of the parasite
• Consumption of raw or undercooked meat containing tissue cysts
• Contaminated water or food with oocysts
• Transplacental (congenital) transmission to the fetus
• Transmission via transplanted organs or blood transfusions

Toxoplasma Forms

• Oocysts:
  • Products of the sexual cycle
  • Shed only by the definitive host (e.g., cats)
  • Sporulate, forming bradyzoites
  • Released by host digestive enzymes
  • Infect intestinal cells, transforming into tachyzoites, which travel via blood/lymph
• Tissue cysts:
  • Packed with bradyzoites
  • Formed when tachyzoites encounter the host's immune response
  • Change back to the bradyzoite form (inactive but can reactivate)

Oocyst Formation and Characteristics

• Formed in the cat's small intestine
• Shed in feces for 10-14 days
• Resistant to external environmental conditions
• Up to 10 million oocysts per day can be shed
• Must sporulate (2-21 days, depending on factors) to become infectious
• May remain infectious for up to 12 months under favorable conditions

Human Infection

• Humans become infected by ingesting tissue cysts or oocysts
• The outer wall of oocysts or cysts is broken down by digestive enzymes
• Parasite is released into the intestinal lumen
• Tachyzoites spread to various body cells and tissues, especially brain and striated muscles
• Bradyzoites form tissue cysts

Toxoplasmosis Lifecycle

• Definitive host (cat) sheds oocysts in feces
• Intermediate hosts (e.g. rodents) ingest oocysts
• Oocysts develop into bradyzoites in the host
• Human infection occurs from consuming tissues of infected animals, or ingesting oocysts

Toxoplasmosis in Humans

• Primary infection is often asymptomatic
• About 10-20% of infected individuals experience a self-limited, nonspecific illness
• Symptoms may include lymph node swelling, muscle pain, and fatigue
• Symptoms can last from days to months
• Tissue cysts remain viable throughout the host's lifetime

Toxoplasmosis in Pregnant Women

• Usually symptomatic
• Tachyzoites can cross the placenta
• Fetal damage is possible, including:
  • Miscarriage or stillbirth
  • Head deformities
  • Brain or eye damage
• Infants may not show symptoms at birth but can later develop issues

Toxoplasmosis in Immunocompromised Individuals

• Reactivation of a previous infection is common
• Often a life-threatening disease
• Brain damage (encephalitis) is frequent
• Symptoms include confusion, nausea, poor coordination, and seizures

Prevention and Control

• Pregnant women and immunocompromised individuals (seronegative) are at highest risk
• Tissue cysts in meats become harmless with proper cooking (to -20°C)
• Wash hands after handling raw meat
• Avoid raw eggs and unpasteurized milk
• Treat cat litterboxes and sandboxes appropriately (daily cleaning prevents)