If the puppy has just been vaccinated, since the vaccine itself is a virus, test paper testing will basically show positive results. Virus incubation period. All test paper is a certain detection limit, when the virus concentration is very low, easy to detect the results can not be found.
This can be characterized by false negative results on the test paper. Carrier of the virus. Some dogs, especially stray dogs, are carriers of the virus themselves, but do not exhibit clinical symptoms. But when you test them with test paper, they are likely to have a positive reaction. This virus carrying dogs, often the environment of other dogs a relatively large threat of infection, but also the canine fever virus in China epidemic and difficult to eliminate the root cause.