The insect which is most likely to transmit infectious encephalitis is:

a. mosquito

b. lice

c. tick

d. flea

Mosquito.

Explanation:

Encephalitis may be defined as the medical condition of the inflammation of brain. The symptoms of encephalitis are fever, headache, confusion and seizures.

The mosquito is mainly responsible for the transmission of encephalitis virus. Japanese encephalitis is transmitted by the bite of the culex mosquito. Ticks are also responsible for transmission of the disease but they are not insects.

Thus, the correct answer is option (a).