**Question:** The vector of Japanese B encephalitis virus is -

A. Mosquito (mainly Culex tritaeniorhynchus)
B. Tick
C. Bird
D. Pig

**Correct Answer:** D. Pig

**Core Concept:**
Japanese B encephalitis (JBE) is a viral infection caused by the Japanese B encephalitis virus (JEV), which belongs to the Flaviviridae family. JEV is transmitted to humans through the bite of an infected mosquito, mainly of the species Culex tritaeniorhynchus. This mosquito is found in Asian countries, particularly in rural areas with rice paddies, which provide a suitable breeding ground for the mosquito.

**Why the Correct Answer is Right:** The correct answer, "Pig," is a reservoir host for the Japanese B encephalitis virus. Pigs act as a source of infection for the mosquitoes, which then transmit the virus to humans through their bites. The role of pigs is essential for the life cycle and maintenance of the virus in nature.

**Why Each Wrong Option is Incorrect:**

A. Mosquito (mainly Culex tritaeniorhynchus) - While mosquitoes are the primary vectors for transmitting JEV to humans, pigs are the reservoir host, providing a continuous source of infection for the mosquitoes.

B. Tick - Ticks are not involved in the transmission of Japanese B encephalitis virus. The virus is transmitted through the bite of infected mosquitoes, primarily Culex tritaeniorhynchus mosquitoes.

C. Bird - Birds are not involved in the transmission of JEV. The virus is primarily transmitted through the bite of infected mosquitoes, specifically Culex mosquitoes.

D. Pig - As mentioned above, pigs are the reservoir host for the Japanese B encephalitis virus, providing a continuous source of infection for the mosquitoes.

**Clinical Pearls:**

Japanese B encephalitis is an important arboviral infection (arthropod-borne viral disease) that affects humans, pigs, and birds. The disease is prevalent in parts of Asia, including countries like India, Bangladesh, Nepal, and Vietnam. Understanding the vector-host-pathogen relationship is crucial for preventing and controlling the spread of JEV. In this case, the correct answer, "Pig," is crucial for understanding the transmission cycle of the virus and the role of mosquitoes in the spread of the disease.