Correct Option: C. River blindness Explanation of the Correct Answer: River blindness, also known as onchocerciasis, is caused by a parasitic worm called Onchocerca volvulus. The transmission of this disease occurs through the bite of infected blackflies, which breed in fast-flowing rivers and streams. Here’s why the farmer cannot contract river blindness in the scenario described:

1. Transmission Method: River blindness is not transmitted through food or water. Instead, it requires a vector (the blackfly) to transfer the parasite from one host to another. Since the farmer did not eat or drink anything, the mode of transmission through food or water is irrelevant.
2. Environmental Factors: The farmer is working in a swamp, which is not the typical habitat for blackflies. They prefer fast-flowing rivers, so even if the farmer were exposed to the environment, the likelihood of encountering the vector is lower in a swamp compared to a river.
3. Lack of Direct Contact: The farmer's lack of food and water intake does not affect his risk of contracting river blindness, as the disease is not related to nutritional or hydration status.

Explanation of Why Other Options Are Incorrect: A. Cholera: - Cholera is an infectious disease caused by the bacterium Vibrio cholerae, primarily transmitted through contaminated water and food. Since the farmer did not drink any water, he is at a lower risk of contracting cholera, but he could still potentially be exposed to contaminated water sources in the swamp. Therefore, he could still contract cholera if he were to consume contaminated water. B. Bilharzia: - Bilharzia, or schistosomiasis, is caused by parasitic worms that live in freshwater. The transmission occurs when a person comes into contact with contaminated water, where the larvae penetrate the skin. Since the farmer is in a swamp, he could still be at risk if he comes into contact with the water, even without drinking it. Thus, he could potentially contract bilharzia. D. Malaria: - Malaria is caused by the Plasmodium parasite, transmitted through the bites of infected female Anopheles mosquitoes. The farmer's lack of food and water does not prevent him from being bitten by mosquitoes in the swamp. Therefore, he remains at risk for malaria regardless of his hydration status. Summary of Key Points:

• River blindness is transmitted by blackflies, not through food or water.
• The farmer's environment (swamp) is less conducive to blackfly presence compared to rivers.
• Cholera and bilharzia can be contracted through contaminated water, while malaria is transmitted by mosquitoes.
• The farmer's lack of food and water does not influence his risk for river blindness, making it the correct answer.

Revision Summary:

• River blindness is vector-borne and not related to food or water intake.
• Cholera and bilharzia are waterborne diseases, while malaria is mosquito-borne.
• Environmental factors influence the risk of disease transmission.
• Understanding transmission routes is crucial for identifying disease risks.