Convert 0-5DC to low current high voltage AC signal
Your 'output' is high impedance - essentially capacitive coupling to the user with capacitance in the order of picoFarads.

So driving a suitably high voltage transistor base or gate with the Arduino and connecting the collector/drain to HV with a resistor and taking the output from collector/drain will allow you to easily swing the voltage across the whole range from full supply to ground.  

Lets assume a bipolar transistor for now - say the venerable TO92 high voltage MPSA42.

If you are able to drive the base with a variable voltage (filtered PWM or DAC output) and you place a resistor Re from emitter to ground  and a resistor Rc from collector to supply then fror HGV supply Vdd:

(Vb-0.6)/Re ~~= (Vdd-Vc)/Rc or

Vc = Vd- (Vb - 0.6) x Rc/Re 

ie the collector voltage decreases away from Vdd by the drive voltage multiplied by Rc/Re.
Drive voltage is 0.6V less than Vb.  

eg for Rb = 1k, Rc = 100k, the collector voltage will drop by 100 volts for every volt of drive or by 1V for every 10 mV of drive.

At say 200V HV (watch transistor rating) max dissispation in Rc = 100k 
= V^2/R =200^2 / 100k = 0.4V.
Also beware max voltage ratings of resistors.  

The wise and prudent will use some form of isolation between Arduino and HV transistor.







simulate this circuit &ndash; Schematic created using CircuitLab

Use of an opamp in the drive circuit allows the approximate 0.6V Vbe to be vanished from the above equations.