Correct Option: A. Aedes mosquito Detailed Explanation: Yellow fever is a viral disease that is transmitted primarily by mosquitoes. The specific vector responsible for the transmission of the yellow fever virus is the Aedes mosquito, particularly Aedes aegypti. Here’s a step-by-step breakdown of why this is the correct answer:

1. Understanding Vectors: A vector is an organism that does not cause disease itself but spreads infection by transmitting pathogens from one host to another. In the case of yellow fever, the Aedes mosquito acts as the vector.
2. Life Cycle of Aedes Mosquito: The Aedes mosquito undergoes a complete metamorphosis, which includes four stages: egg, larva, pupa, and adult. The adult female mosquito requires blood meals to develop her eggs, and during this process, she can pick up the yellow fever virus from an infected person or animal.
3. Transmission Mechanism: When an Aedes mosquito bites a person infected with the yellow fever virus, it ingests the virus along with the blood. The virus then replicates within the mosquito. After a period of time, the mosquito can transmit the virus to another person through its saliva when it bites again. This is how the disease spreads in human populations.
4. Geographical Distribution: Aedes mosquitoes are commonly found in tropical and subtropical regions, which are also the areas where yellow fever outbreaks occur. This correlation between the habitat of the Aedes mosquito and the incidence of yellow fever further supports the identification of this mosquito as the primary vector.

Why Other Options Are Incorrect:

• B. Anopheles mosquito:
• The Anopheles mosquito is primarily known as the vector for malaria, not yellow fever. While it is a significant vector for other diseases, it does not transmit the yellow fever virus. This makes it an incorrect option.
• C. Tsetse fly:
• The tsetse fly is the vector for African sleeping sickness (trypanosomiasis). It is not involved in the transmission of yellow fever. Therefore, this option is also incorrect.
• D. Blackfly:
• Blackflies are known to transmit river blindness (onchocerciasis) but are not associated with yellow fever transmission. This makes this option incorrect as well.

Summary of Key Points:

• The Aedes mosquito (especially Aedes aegypti) is the primary vector for yellow fever.
• Vectors are organisms that transmit pathogens without causing disease themselves.
• The transmission of yellow fever occurs when an infected Aedes mosquito bites a human, allowing the virus to spread.
• Other options (Anopheles mosquito, tsetse fly, blackfly) are associated with different diseases and do not transmit yellow fever.

Revision Summary:

• Yellow fever is transmitted by the Aedes mosquito.
• Vectors are crucial for the spread of many infectious diseases.
• Aedes mosquitoes thrive in tropical and subtropical regions, correlating with yellow fever outbreaks.
• Other mosquito species and flies mentioned do not transmit yellow fever, highlighting the specificity of disease vectors.