Correct Answer: B. Man acts as the reservoir
Japanese encephalitis (JE) is a zoonotic arboviral disease endemic across Asia, including India (particularly in eastern and northern regions). The critical distinction in JE epidemiology is the difference between reservoir host and amplifier host. Man is NOT the reservoir; he is an accidental/dead-end host. The true reservoir hosts are birds (especially wading birds and herons), which maintain persistent viremia without clinical disease and serve as the long-term source of infection. Pigs act as the amplifier host—they develop high viremia when infected, facilitating transmission to mosquitoes, which then spread the virus to humans. This is why vaccinating pigs (with inactivated JE vaccines) breaks the transmission cycle and is a proven control strategy in endemic areas like Japan and parts of India. Humans, by contrast, develop clinical disease but do not sustain the virus in the community; they are epidemiological dead-ends. The vector is Culex vishnui (and related Culex species), which breeds in rice paddies and stagnant water—the reason JE peaks during monsoon and post-monsoon seasons in India. Understanding this reservoir-amplifier-vector triad is fundamental to JE control and is tested repeatedly in NEET PG.
Why the other options are wrong
A. Vaccinating pigs is helpful in disease control — This statement is TRUE and is a cornerstone of JE control strategy. Pig vaccination reduces viremia in the amplifier host, breaking the transmission cycle to vectors and humans. This is practiced in endemic countries and is supported by WHO guidelines. Selecting this as 'not true' is incorrect. C. Pig is the amplifier host — This is TRUE. Pigs develop high viremia and are the principal amplifier host in the JE transmission cycle. They are not the reservoir (birds are), but they are essential for amplifying virus levels in the environment. This is a well-established epidemiological fact in JE. D. Transmitted by Culex vishnui — This is TRUE. Culex vishnui is the primary vector for JE in India and Asia, along with Culex tritaeniorhynchus. The vector breeds in rice paddies and stagnant water, explaining the seasonal and geographic distribution of JE. This is a factual statement about JE transmission.
High-Yield Facts
- Reservoir host of JE: Birds (herons, wading birds), NOT man—man is an accidental dead-end host.
- Amplifier host of JE: Pig—develops high viremia and amplifies virus for vector uptake.
- Vector: Culex vishnui (and Culex tritaeniorhynchus)—breeds in rice paddies, peaks monsoon–post-monsoon.
- Pig vaccination: Reduces viremia in amplifier host, breaks transmission cycle—proven control strategy in endemic areas.
- JE in India: Endemic in eastern (West Bengal, Assam) and northern states (UP, Bihar); seasonal pattern correlates with rice cultivation and vector breeding.
Mnemonics
RAV for JE epidemiology Reservoir (Birds) → Amplifier (Pig) → Vector (Culex vishnui) → Man (dead-end). Use this to remember the transmission chain and why man is NOT the reservoir. PIG-JE control Pig vaccination, Insecticide spraying, Genetic control of vectors. Pig vaccination is the most effective because it targets the amplifier host.
NBE Trap
NBE exploits confusion between 'reservoir host' (maintains virus long-term) and 'amplifier host' (increases virus levels). Students who conflate man's clinical prominence with epidemiological importance may incorrectly think man is the reservoir, missing the correct answer.
Clinical Pearl
In India, JE outbreaks in eastern states (West Bengal, Assam) correlate with rice cultivation and pig farming—understanding the amplifier role of pigs explains why pig vaccination campaigns have reduced JE incidence in endemic districts. A patient presenting with encephalitis during monsoon season in a rice-farming region should raise suspicion for JE.
_Reference: Jawetz, Melnick & Adelberg's Medical Microbiology Ch. 43 (Arboviruses); Park's Textbook of Preventive and Social Medicine Ch. 7 (Communicable Diseases)_