As someone who has had Giardia (including one episode that put me in the hospital when I was in vet school), I know how bad it can be. However, my concern about the human health risks from dogs with Giardia has been pretty low. Giardia comes in several different “assemblages” (types) and these types like different hosts. Types C and D are considered canine-specific (i.e. they only infect dogs), and its been assumed that dogs with these pose little to no risk to people.
A recent report from Slovakia probably doesn’t change that dramatically, but it does raise some questions.
The paper in question is a case report describing human infection with Assemblage C Giardia in a person (Strkolcova et al Acta Parasitol 2015). The woman had chronic diarrhea and some other signs of illness, and Giardia was seen microscopically in her stool. Subsequent testing then identified it as Assemblage C.
I’d avoid reading too much into a single case report. It’s possible that she was shedding this strain of Giardia but something else was causing her illness, or that she had some unusual risk factor, or that this wasn’t really Assemblage C, or that this is a one-in-a-million situation. However, it means we should pay attention and realize that (as is common) things are not always as definitive as we’d like to think.