Correct Option
The correct option is (b).
Explanation
In epidemiology and pathology, a carrier is an organism that harbors a specific infectious agent without demonstrating distinct clinical symptoms of the disease and serves as a potential source of infection for others. Vectors are organisms that transmit pathogens from one host to another.
Statement-wise Analysis
- Statement 1 is Incorrect. A carrier does not die immediately upon contracting a pathogen. By definition, a carrier survives and harbors the pathogen, often asymptomatically, allowing the pathogen to be transmitted to other susceptible hosts over time. If the host died immediately, the transmission chain would break.
- Statement 2 is Correct. The housefly acts as a mechanical carrier. Pathogens from garbage and excreta stick to its legs and body hairs. When the fly lands on uncovered food, these pathogens are physically transferred, potentially causing diseases like cholera and typhoid.
- Statement 3 is Incorrect. While it is factually true that mosquitoes breed in stagnant water, this is not the reason they are classified as carriers or vectors. They are classified as vectors because they carry pathogens (such as the Plasmodium parasite or Dengue virus) within their bodies and transmit them to humans through bites. The breeding habitat is an ecological characteristic, not the functional definition of their role in disease transmission.
Key Takeaway
Carriers (like houseflies) physically transport pathogens, whereas vectors (like mosquitoes) often serve as biological hosts where the pathogen may multiply or develop before transmission. A carrier is defined by its ability to transmit disease, not by its mortality rate or breeding grounds.