For which virus is the mosquito not known as a possible vector?

The reason why the correct answer is Smallpox pertains to the transmission methods of the virus. Smallpox is caused by the variola virus, which is primarily spread between humans through respiratory droplets and direct contact with contaminated materials or infected individuals. It does not involve any vector such as mosquitoes in its transmission cycle.

In contrast, the other viruses listed—West Nile Virus, Zika Virus, and Dengue Virus—are all transmitted by mosquitoes. Specifically, the Aedes and Culex species of mosquitoes serve as vectors for these viruses, facilitating their spread through bites that transfer the virus from the mosquito to the host. Understanding the transmission pathways is critical in epidemiology and public health because it informs prevention strategies against these infectious diseases.