Could be Parvo but too perky?
Parvo is tested for in a fecal sample.
Metronidazole is used to treat Giardia in dogs-yes bacteria & more but...
Metronidazole has also been known to be toxic for small dogs, so please read the links and know what to watch for.
I'm no expert but I hope someone more informed that I will post here with their experience.
Metronidazole for Dogs ? Is It Safe To Use? Metronidazole for Veterinary Use