What is Wernicke’s encephalopathy is due to deficiency of: and explain in detail?
Thiamine deficiency:
In the developed world, thiamine deficiency is mainly encountered in chronic alcoholics. Poor diet, impaired absorption, storage and phosphorylation of thiamine in the liver, and the increased requirements for thiamine to metabolise ethanol all contribute.
In the developing world, deficiency usually arises as a consequence of a diet based on polished rice. The body has very limited stores of thiamine, so deficiency manifest after only 1 month on a thiamine-free diet. There are two forms of the disease in adults: 

Dry (or neurological) beri-beri manifests with chronic peripheral neuropathy and with wrist and/or foot drop, and may cause Korsakoff's psychosis and Wernicke's encephalopathy.
Wet (or cardiac) beri-beri causes generalised oedema, due to biventricular heart failure with pulmonary congestion. 

In dry beri-beri, response to thiamine administration is not uniformly good. Multivitamin therapy seems to produce some improvement, however, suggesting that other vitamin deficiencies may be involved. Wernicke's encephalopathy and wet beri-beri should be treated without delay with intravenous vitamin B and C mixture. Korsakoff's psychosis is irreversible and does not respond to thiamine treatment. 
 Ref: Davidson Ed 23 Pg 714