The use of ELISA and Real Time PCR for the detection of PCV2

The interpretation of the ELISA or PCR results for PCV2 detection is often difficult. The aim of the study was to compare PCV2 seroconversion, viremia, shedding in feces and presence in oral fluid in three Polish farms.

The serum, feces and oral fluid samples were obtained from two, two site farms with low level of biosecurity and hygiene (farm 1 and farm 2), and from one farrow-to-finish farm with very high biosecurity level and hygiene (farm 3). In farm 2 and 3 piglets at 3 weeks of age were vaccinated against PCV2 with CircoFLEX (Boehringer Ingelheim). The samples were obtained from 3 (except for farm 2), 6, 9, 12, 15, 18 and 21 week old pigs and sows (except for farm 2). From each age group 8-10 serum samples were obtained, as well as feces samples from the bled pigs. Also one oral fluid sample was collected per pen of weaners and fatteners. In three-week-old piglets, oral fluid was collected individually with a cotton swab. Serum samples were analysed with Ingezim Circovirus IgG/IgM ELISA (Ingenasa). Serum, feces and oral fluid samples were analysed with in house Real Time PCR for PCV2.

In farm 1, despite no vaccination against PCV2, the nursery population seemed free from the infection until 9 weeks of age. PCV2 was detected in serum, feces and oral fluid at site 2, in all animals from 12 to 21 weeks of age, as well as IgG and IgM seroconversion in majority of fatteners.

In farm 2 PCV2 in serum and feces was detected respectively in 2 and 12, out of 20 weaners, as well as in oral fluid. At site 2 of farm 2 viremia was less common, and Ct values higher, than at the site 2 of farm 1, where pigs were not vaccinated (52.5% vs 97.5% of viremic pigs, in farm 2 and farm 1, respectively). Despite infection of weaners and fatteners in farm 2, only 3 out of 60 serum samples were IgM positive.

In farm 3 viremia was detected in one sow and in oral fluid of 12-week-old fatteners. All other samples were negative in Real Time PCR. Seroconversion with IgG was present in sows and 3 to 12-week-old pigs. The result of PCV2 presence at low level in 2 out of 128 samples of serum and feces and 15 oral fluids is difficult to interpret.

In summary, serological and real-time PCR results for PCV2 have to be interpreted with care. Real Time PCR proves to be the best method for evaluation of PCV2 circulation. Vaccination seems to limit PCV2 viremia to a larger extent than its shedding in feces. Considering the ease of sampling and the results of this study, feces or oral fluid should be considered as best samples for Real Time PCR monitoring of PCV2, especially in vaccinated farms

Disclosure of Interest: None Declared.