Life Cycle of Toxoplasma Gondii

Life Cycle of Toxoplasma Gondii

• Merozoites are responsible for expanding the parasite inside the cat intestine prior to sexual reproduction.
• Sporozoites are the stage of the parasite residing within oocysts.
• Gametocytes (male and female) are formed during the schizogonic phase in the cat's intestine.

Hosts and Transmission

• The only known definitive host for Toxoplasma gondii is the domestic cat and its relatives in the family Felidae.
• Large numbers of unsporulated oocysts are shed in the cat's feces, which take 1-5 days to sporulate in the environment and become infective.
• Intermediate hosts (birds and mammals) become infected after ingesting soil, water, or plant material contaminated with mature oocysts containing sporozoites.
• Humans can become infected by:
  • Eating undercooked meat of animals harboring bradyzoites in tissue cysts.
  • Blood transfusion or organ transplantation.
  • Transplacentally from mother to fetus.
  • Consuming food or water contaminated with oocysts containing mature sporozoites.

Infection and Disease

• Toxoplasma gondii is an intracellular parasite that can actively enter any nucleated cell in the host body.
• It disseminates through the host body with infected mobile cells, such as dendritic cells and monocytes, using a "Trojan horse" strategy.
• Infection can lead to diseases, including:
  • Encephalitis with large foci of necrosis in gray matter.
  • Other neurologic diseases.
  • Pneumonia.
  • Myocarditis.
  • Eye diseases.

Epidemiology

• Serologic prevalence data indicates that toxoplasmosis is one of the most common human infections worldwide.
• Regional seroprevalence rates:
  • Latin America: 50-80%.
  • Eastern and Central Europe: 20-60%.
  • Middle East: 30-50%.
  • Southeast Asia: 20-60%.
  • Africa: 20-55%.

Clinical Manifestations

• Healthy people infected with T. gondii often do not show symptoms, as their immune system keeps the parasite from causing illness.
• Acute illness is usually mild, with "flu-like" symptoms, and resolves on its own.
• Infants, pregnant women, and immunocompromised people are more vulnerable to severe toxoplasmosis.
• Severe toxoplasmosis can cause CNS complications, pneumonia, myocarditis, and eye diseases.

Laboratory Diagnosis

• Diagnosis of toxoplasmosis in humans is made by:
  • Clinical (physical) examination.
  • Serological methods (specific antibody detection from serum).
  • Histological methods.
  • Molecular methods.