I emailed John May, a leading microbiologist with an interest in breastmilk
about our giardia discussion.  He has an excellent web page on the
anti-bacterial,-viral,-protozoal properties of breastmilk and contaminants
in both breastmilk and formula which is worth having a look at.  The address
is:  http://www.latrobe.edu.au/www/microbio/milk.html
here is his reply to my question:
Denise,
I know of no giardia being passed through or in the milk. I would like to
see what was said in that publication. (I mentioned Lawrence, Denise)  I try
to keep my lists as uptodate
as possible and chek the medline today, but I would have found it quoted by
others if it had. Yes there are antibodies and lipids will kill it as
listed on the tables.
It may be like the tubercolosisi situation . Although ther is no recent data
Tb was said to be passesd through milk and old nurses warned mothers
against it but no data is availble. My lsitind is from a statement that TB
can be in the milk, and the paediatrics Sosoieties list is as one where the
mother should not breast feed. Syphilis is another one and I can only find
that lesions may appear on the nipple and that is why and I have never
found any direct evidence.

Possibly giardia may be onre of these lkind of "hearsay'over the years without
any direct evidence (parasites are very rarely found even if the nmilk is
suspected of being a source)
I hope this is of some help and contact me whenever
best wishes
john