What is the mechanism by which mosquitoes transmit diseases?

Mosquitoes transmit diseases primarily through their saliva and the act of blood feeding. When a mosquito bites an individual, it injects saliva into the bloodstream. This saliva contains various enzymes and anticoagulants that facilitate blood flow, but it is also a vehicle for pathogens such as viruses and parasites. Diseases like malaria, dengue fever, and Zika virus are examples of illnesses that can be transmitted in this way.

In addition to the saliva, the process of blood feeding is crucial. As mosquitoes feed, they can introduce these pathogens directly into the host's circulatory system, leading to infection. This method of transmission is efficient, as it allows the mosquito to spread diseases while simultaneously sourcing the nutrients necessary for egg production.

The other options do not accurately describe the disease transmission mechanism associated with mosquitoes. Pheromones are chemical signals used for communication, typically not linked to disease transmission. Direct contact refers to the transfer of pathogens between hosts without an intermediary, which does not apply to mosquito-borne diseases. Contaminated water can spread certain illnesses, but that is more relevant to diseases spread by waterborne pathogens, not those transmitted by mosquito bites. Therefore, the correct answer accurately reflects the specific and significant role of saliva and blood feeding in the transmission of