Which of the following is considered a vector for disease transmission?

In the context of disease transmission, a vector is typically defined as an organism that transmits pathogens from one host to another without causing disease itself. Insects, such as mosquitoes, ticks, and fleas, are classic examples of vectors, as they can carry and spread infectious agents—such as viruses, bacteria, or parasites—through their bites. For instance, mosquitoes are well-known vectors for diseases like malaria and dengue fever, as they can transfer the pathogens from an infected individual to a healthy one during feeding.

While contaminated food, infected animals, and water sources can indeed be involved in the transmission of diseases, they aren't classified as vectors. Contaminated food and water directly spread pathogens through ingestion, and infected animals can serve as a source of infection but usually through direct contact or through the consumption of animal products. In contrast, vectors specifically facilitate the transfer of disease agents between hosts, which is why insects are categorized as true vectors.