Select the correct statement with respect to disease.

Options

A. Injection of snake antivenom against snakebite is an example of active immunisation.
B. Certain protozoans have been used to produce Hepatities - B vaccine
C. If B and T - lymphocytes are destroyed due to an unknown reason, the body will not be able to produce antibodies against a pathogen
D. Injection of dead / inactivaed pathogen causes passive immunity.

Answer

To solve the question, we need to evaluate each statement regarding diseases and immunity to determine which one is correct.

### Step-by-Step Solution:

1. **Evaluate Statement 1**: "Injection of snake antivenom against snake bite is an example of active immunization."
- **Analysis**: Active immunization involves the introduction of an antigen that stimulates the body to produce its own antibodies. In the case of snake antivenom, ready-made antibodies are injected into the body to neutralize the venom. Therefore, this is an example of passive immunization, not active immunization.
- **Conclusion**: This statement is **incorrect**.

2. **Evaluate Statement 2**: "Certain protozoans have been used to produce hepatitis B vaccine."
- **Analysis**: Hepatitis B is caused by a virus (hepatitis B virus), not a protozoan. Vaccines for hepatitis B are typically made using viral components, not protozoans.
- **Conclusion**: This statement is **incorrect**.

3. **Evaluate Statement 3**: "If B and T lymphocytes are destroyed due to an unknown reason, the body will not be able to produce antibodies against a pathogen."
- **Analysis**: B lymphocytes are responsible for producing antibodies, while T lymphocytes play a crucial role in the immune response. If both types of lymphocytes are destroyed, the body indeed cannot produce antibodies against pathogens.
- **Conclusion**: This statement is **correct**.

4. **Evaluate Statement 4**: "The injection of dead inactivated pathogen causes passive immunity."
- **Analysis**: The injection of dead or inactivated pathogens stimulates the immune system to produce its own antibodies, which is an example of active immunity. Passive immunity involves the direct transfer of antibodies.
- **Conclusion**: This statement is **incorrect**.

### Final Conclusion:
The correct statement is **Statement 3**: "If B and T lymphocytes are destroyed due to an unknown reason, the body will not be able to produce antibodies against a pathogen."

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