64 bits integers cannot be represented in JSON since JavaScript internally codes values as 64 bits floating point values (http://ecma262-5.com/ELS5_HTML.htm#Section_8.5).
Thus, you are limited to 53 bits of precision (2^53).
If you want to exchange 64 bits integers, you may use strings or split the 64 integer in two 32 bits integers and then recombine them (What is the accepted way to send 64-bit values over JSON?).