Explain antigenic masking and variation. List the three transmission mechanisms of Toxoplasma gondii and the three infectious stages it has for cats.

Here's the answer to question 14:

• 14. (a) What do you understand by 'antigenic masking' and 'antigenic variation'?

  • Antigenic masking is a strategy used by some parasites to evade the host's immune system by coating themselves with host molecules. This makes the parasite appear as "self" to the immune system, preventing an immune response against its own antigens.
  • Antigenic variation is the process by which a parasite changes the expression of its surface antigens over time. This allows the parasite to escape detection by antibodies previously generated by the host's immune system, leading to persistent infection.

• 14. (b) i. Trypanosoma gondii is transmitted by three (3) distinct mechanisms. These are? (Assuming this is a typo and refers to Toxoplasma gondii) The three distinct mechanisms of transmission for Toxoplasma gondii are:

  • Ingestion of oocysts: From contaminated food, water, or soil, often from cat feces.
  • Ingestion of tissue cysts (bradyzoites): From undercooked meat of infected animals (e.g., pork, lamb, venison).
  • Congenital transmission: From an infected mother to her fetus during pregnancy.

• 14. (b) ii. Cats acquire Toxoplasma by ingesting any of the three infectious stages of the organism. These are? The three infectious stages of Toxoplasma gondii that cats can ingest are:

  • Sporulated oocysts: Found in the environment, shed in the feces of other infected cats.
  • Bradyzoites: Contained within tissue cysts in the meat of infected intermediate hosts (e.g., rodents, birds).
  • Tachyzoites: Less commonly, from the tissues of acutely infected prey.