Question:
Given below are two statements:
Statement (I): The animals infected with Theileria annulata are cross-protected against Theileria parva infection.
Statement (II): Protective immunity in Theileria parva is conferred by cytotoxic T lymphocytes which cause lysis of parasites by osmotic alteration in target cells leading to swelling and disruption of the cells.
In light of the above statements, choose the most appropriate answer from the options given below.
Given below are two statements:
Statement (I): The animals infected with Theileria annulata are cross-protected against Theileria parva infection.
Statement (II): Protective immunity in Theileria parva is conferred by cytotoxic T lymphocytes which cause lysis of parasites by osmotic alteration in target cells leading to swelling and disruption of the cells.
In light of the above statements, choose the most appropriate answer from the options given below.
Statement (I): The animals infected with Theileria annulata are cross-protected against Theileria parva infection.
Statement (II): Protective immunity in Theileria parva is conferred by cytotoxic T lymphocytes which cause lysis of parasites by osmotic alteration in target cells leading to swelling and disruption of the cells.
In light of the above statements, choose the most appropriate answer from the options given below.
Show Hint
Humoral antibodies play a negligible role in protecting against the intracellular schizont stage of *Theileria parva*.
Protective immunity is almost entirely mediated by CD8+ Cytotoxic T Lymphocytes (CTLs).
Protective immunity is almost entirely mediated by CD8+ Cytotoxic T Lymphocytes (CTLs).
Updated On: Jul 14, 2026
- Both Statement (I) and Statement (II) are correct.
- Both Statement (I) and Statement (II) are incorrect.
- Statement (I) is correct but Statement (II) is incorrect.
- Statement (I) is incorrect but Statement (II) is correct.
Show Solution
Verified By Collegedunia
The Correct Option is D
Solution and Explanation
Step 1: Understanding the Concept:
Theileria annulata (causing Tropical Theileriosis) and Theileria parva (causing East Coast Fever) are two distinct tick-borne protozoan parasites of cattle.
They are geographically separate and possess different antigenic properties.
Detailed Explanation:
Let us evaluate both statements:
Statement (I): Theileria annulata and Theileria parva are antigenically distinct species.
Recovery from infection or vaccination against T. annulata does not provide significant cross-protection against a subsequent challenge with T. parva.
Vaccination and control programs must target the specific species relevant to the region.
Thus, Statement (I) is incorrect.
Statement (II): Protective immunity against East Coast Fever (T. parva) is primarily mediated by cell-mediated immunity.
Specifically, MHC class I-restricted CD8+ cytotoxic T lymphocytes (CTLs) target and destroy schizont-infected lymphocytes.
The CTLs release cytolytic granules (perforins and granzymes) onto the target cell membrane.
Perforin molecules polymerize to form pores, causing uncontrolled water influx, osmotic swelling, lysis, and destruction of the infected host cell.
Thus, Statement (II) is correct.
Therefore, Statement (I) is incorrect but Statement (II) is correct.
Step 2: Final Answer:
The correct option is (D).
Theileria annulata (causing Tropical Theileriosis) and Theileria parva (causing East Coast Fever) are two distinct tick-borne protozoan parasites of cattle.
They are geographically separate and possess different antigenic properties.
Detailed Explanation:
Let us evaluate both statements:
Statement (I): Theileria annulata and Theileria parva are antigenically distinct species.
Recovery from infection or vaccination against T. annulata does not provide significant cross-protection against a subsequent challenge with T. parva.
Vaccination and control programs must target the specific species relevant to the region.
Thus, Statement (I) is incorrect.
Statement (II): Protective immunity against East Coast Fever (T. parva) is primarily mediated by cell-mediated immunity.
Specifically, MHC class I-restricted CD8+ cytotoxic T lymphocytes (CTLs) target and destroy schizont-infected lymphocytes.
The CTLs release cytolytic granules (perforins and granzymes) onto the target cell membrane.
Perforin molecules polymerize to form pores, causing uncontrolled water influx, osmotic swelling, lysis, and destruction of the infected host cell.
Thus, Statement (II) is correct.
Therefore, Statement (I) is incorrect but Statement (II) is correct.
Step 2: Final Answer:
The correct option is (D).
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