In this study 6 pups from immunized bitches were vaccinated against canine parvovirus type 2 in the 8 and 12 postnatal weeks. Attenuated live vaccine viruses are very similar to pathogen field viruses, may be excreted and the frequently used diagnostic methods like ELISA, IC-test or PCR lack specificity in order to distinguish between vaccine and field viruses. This may lead to a misinterpretation of positive test results of newly vaccinated pups. thth
In order to get detailed information about this problem we used 2 different vaccines and observed the faecal shedding of vaccine virus in regard to quantity and duration. We applied the realtime-PCR and the IC-test and used the HI-test to demonstrate seroconversion.
During the whole investigation period of 43 days CPV-2 DNA was detected by realtime-PCR in 117 (60.9%) out of 192 samples. As already samples of the first day of the study, which had been collected before the vaccination was carried out, contained CPV-2 DNA, a subclinical field infection had to be suspected.
Using the IC-test no CPV-2 was detectable during the whole period of the study. The subclinical infection which was already present at the beginning of the investigation resulted in a well developed immunity of the pups. Hence, CPV-2 particles may have been conjugated by antibodies with the result that viral antigen in the faeces could not be detected using the IC-test. Hence, this study did not give any information about the extent to which the IC-test will be influenced by attenuated live vaccines.
In order to get more information about the subclinical field infection sequence analyses were carried out. 20 out of the 117 positive samples contained sufficient amounts of DNA for achieving sequences, which showed that both the DNA of the vaccine virus and of a CPV-2 field virus was shed. DNA from the field virus was detectable until the 11 day of the study. However, vaccine strain DNA was detectable on day 28 (before the second vaccination) in the faecal samples of 2 pups and finally until the 34 day. ththPositive PCR results were achieved until day 43, but in these samples sequence analyses were not successful anymore. As a result it can be stated that the DNA of attenuated live CPV-2 is shed until the 28 day after vaccination at least.