I have been lurking on these forums for a while and joined just to reply to this post. I have, sadly, pretty extensive experience with parvo, and would like to share what I've learned. This will be a long post.
Testing: previous vaccination can cause false positives. The Idexx snap test generally does not show a false positive, but can show a false negative if the pup has been sick for more than a couple of days. Pups will start shedding virus several days before showing symptoms, and usually only shed virus for a couple of days past that point. Pups can shed virus in the stool for around three weeks, though it's usually much shorter.
Maternal antibodies: Mom produces colostrum, which contains antibodies, when the pups are born. Pups are only capable of absorbing these antibodies during the first twenty-four hours of life (there is not a general consensus on this. It could be a shorter time period.) How long the MAs last is dependent on how much immunity mom has to pass on and how well the puppy nursed during the first day of life. You can check the titer of mom, either right after or right before birth, and tell approximately when a vaccine will 'take' for the pups. MAs drop by approximately half for each week of the pups life. There is a period where there is enough MA to interfere with a vaccine, but not enough to protect the pup from illness; this is why we do multiple vaccines. So, in short, duration of nursing has nothing to do with when the MA will wane enough for a pup to get sick. Many breeders supplement their pups with fresh frozen plasma, available from Hemopet, at birth to make sure they get plenty of antibodies; the catch with this is that such pups will have MAs for longer, meaning it will take longer for vaccination to produce protection.
Vaccination: Reasons vaccines fail: too early (MA kills the vaccine), improper storage, overwhelming challenge dose. Yes, it is possible for a pup to be exposed to so much virus that it overwhelms the immunity provoked by vaccination. It is possible to tell if a pup has seroconverted (formed antibodies to the virus) by doing a titer test around two weeks after vaccination if you are concerned about giving too many vaccines. 95% of pups vaccinated after the age of twelve weeks will successfully seroconvert, the other 5% will not no matter how many vaccines they are given. That doesn't guarantee that non-responders will get sick, though. Vaccines containing the 2b virus are cross-protective against all strains. There is a new strain, 2c, which can be carried by cats and is present iin the United States. Single antigen vaccines work better than multi-valent vaccines, because the former contains more antigen of a single disease than the latter, making a single antigen vaccine more likely to break through MA.
Treatment: I have used both Parvaid, which is an herbal medication, and Tamiflu, which is a prescription human flu medication, successfully. By far my first choice is Tamiflu. For small pups the suspension (liquid) form can be used, for large pups the capsules can be put into suspension. Tamiflu is, in the long run, cheaper than Parvaid, which I feel is grossly overpriced, and it works much, much faster. Tamiflu suspension is about $46, ten 75 mg capsules about $100. Dosage is 1 mg per pound, 2 mg if the vomiting does not stop after one dose. The catch is the Tamiflu works best if administered within the first twenty-four hours, which is useful for the second pup that gets sick but not so much for the first one unless it is caught and tested early. Tamiflu can be used to keep other exposed pups from getting sick. It is administered twice a day to treat a sick pup, once a day for prevention. Parvo basically kills the host pups immunity, and the gastroenteritis is caused by overgrowth of bacteria. Tamiflu stops the bacterial process. Parvaid does work, quite well, however it is not only very expensive (you will need at least two bottles to treat a litter of pups, more if they are big pups,) but it is labor intensive, as you must administer it every hour until the pup stops vomiting. I have had some pups react to the alcohol in the tincture by vomiting, so it helps to sweeten it with honey before giving it.
Disinfection: Parvo lives for about a month indoors. It likes moist, dark areas. Sunlight will kill it. One half cup (four ounces) of household bleach to a gallon of water will kill it. Trifectant (brand name) will kill it, and works better in the presence of dirt and other organic material than bleach. Both work best if you saturate the area and let it sit for a while. Scrubbing the area works even better. Parvo can persist for months outdoors if no disinfection is done. Parvo is also considered endemic in the environment in the US, meaning it's assumed to be there if no disinfection has been done.
Transmission: Parvo can be carried on shoes, in blowing dirt, by birds and flies, or directly transmitted via vomit or feces. It only takes a tiny, tiny bit to cause illness. Bleach baths for shoes do not work, booties or changing shoes are a better choice, spraying shoes with Trifectant, then scrubbing and spraying again may work.
Links:
Parvaid:
Using Tamiflu for parvo
Disinfecting
My recommendation for people who have pups in a high risk area is to connect with your vet and discuss treatment and early diagnosis before hand. If I were a breeder or rescuer in a high risk area I would keep Idexx snap tests (around $90 for five) and Tamiflu capsules on hand. It's a small investment compared to the cost of treatment for a very sick pup, or worse, losing the pup. If a pup tests positive, Tamiflu can than be started immediately.
Good luck.
