Although the classical gross and histopathological lesions associated with PMWS were described over a decade ago, the definitive diagnosis of PCVD in individual pigs is not always simple. In individual cases, the classical clinical signs (wasting, diarrhea, dyspnea, lymphomegaly, jaundice), histopathological lesions (granulomatous inflammation, lymphoid depletion) and PCV2 antigen associated with the lesions must be evident. However, the presence of simultaneous infections often makes diagnosis difficult. In these cases, diagnostic results may yield multiple viral or bacterial pathogens in addition to PCV2, and the significance of each must be ascertained.
Another complicating factor in the diagnosis of PCVD is that PCV2 may be present, albeit at low levels, in the tissues of sub-clinically infected but seemingly healthy pigs. Thus, antibody testing in serum is not an effective tool to determine if a farm or pig is affected by PCVD. It only shows that PCV2 is present in a herd or that a pig was exposed. However, quantifying the levels of PCV2 in tissues may be useful in ascertaining the significance of PCV2 infection. Good production practices might help to reduce the impact of PCVD and coinfections. Thus, the MADEC 20 principles were at least partially effective in controlling PMWS in many European herds prior to the use of PCV2 vaccine. However, the concensus view is that the use of PCV2 vaccines, led to the rapid decline in the number of PCVD herd epizootics in North America in 2007. To judge the efficacy of a vaccine in the field, reduction of mortality, reduced number of culls and improved performance are the most relevant parameters. Based on these the economical benefit of piglet vaccination can be estimated, and is reported to be as high as 9.85 USD in a non-complicated case of PCVD. Importantly, the piglet vaccines are efficacious in the presence of maternal antibodies, and when coinfections including PRRS59, and Mycoplasma hyorhinis exist. Moreover, there appears to be cross-protection between the two PCV2 genogroups. Thus, the North American and the global swine industries are very fortunate, in that effective PCV2 vaccines are now widely available, and enhance the profitability of pork production systems