Decimal Sign Replaced with ; Sign

Hi to all,

I'm trying to solve a strange problem in a piece of code.
I have a variable that is define as Double called STD. When i try to insert that variable in a formula the decimal sign (for me a comma "," because I'm Portuguese) gets converted to ";" (which is for me the separation sign for the expressions in excel formulas. ex: AND(A1>0;B1>0)=TRUE). The code is:

Public STD as Double
STD = ActiveSheet.Cells(n, NUMBEROFASSETS + 5).Value
ActiveSheet.Cells(m + 1, n + TOPPAIRS + NUMBEROFASSETS + 7).Formula = "=IF(AND(INDEX(" & SPREAD & "," & m + 1 & "," & n & ")>" & STD & "," & ANT & "=0)=TRUE,-1,IF(AND(INDEX(" & SPREAD & "," & m + 1 & "," & n & ")<-" & STD & "," & ANT & "=0)=TRUE,1,IF(AND(" & ANT & "<>0,SIGN(INDEX(" & SPREAD & "," & m + 1 & "," & n & "))<>SIGN(INDEX(" & SPREAD & "," & m & "," & n & ")))=TRUE,0,IF(AND(" & ANT & "<>0,INDEX(" & SPREAD & "," & m + 1 & "," & n & ")="""")=TRUE,0,IF(" & ANT & "<>0," & ANT & ",0)))))"

Can anyone help me preventing this automatic conversion?
Thanks in advance for any advice.

Edit: I must add, i have tried to convert the sign before using the variable in the formula but with no success. I tried this:

STD = SUBSTITUTE(STD,"","",""."")