Work shows PCV-2 virus here 15 years
PORCINE circovirus type 2 (PCV-2), which is implicated in PMWS and PDNS, may have been present in the UK for the past 15 years.
But it has only recently been recognised, researcher Gordon Allan, of Northern Irelands State Vet Division told an MLC/NPA seminar on PDNS/PMWS.
PCV-2 associated diseases have exploded in the last three years, but the reason is unclear, he added.
However, Dr Allan believes a number of other pig diseases may also be linked with the virus, including myocarditis and post-weaning porcine respiratory and reproductive syndrome (PRRS).
PCV-2 has been strongly indicated as the cause of PMWS, which is linked to PDNS, said the Vet Lab Agencys Andrew Gresham. "But virus plus pig does not necessarily mean the disease will occur.
"This is supported by evidence of PCV-2 infection in pigs without clinical symptoms of PDNS/ PMWS. PDNS has possibly been in the UK since the mid-1980s."
In experimental conditions, infecting pigs with PCV-2 alone only caused mild lesions and no clinical disease, said Dr Allan. "But certain animals appear to be susceptible to PMWS. In one experiment, all pigs undergoing immuno-stimulation went on to develop clinical PMWS when infected with PCV-2.
"This suggests activating the immune system switched the disease on. Therefore, the presence of other viruses, such as E coli and porcine parvovirus, or vaccination could be a trigger for PMWS."
An ongoing Italian field study found removing one vaccination event helped reduce losses. But the vaccination programme was being undertaken on the farm before PMWS appeared, he said.
The timing of immunity being passed on to piglets against circoviruses is important, said East Anglia-based vet Roger Harvey. "Moving vaccination from weaning was a big help on several farms. Prior to this stress, mixing and immune challenge were all happening at the same time, increasing disease susceptibility,"he added. *
Dr Allan also presented preliminary results showing evidence of maternal antibody transfer protecting piglets against PMWS. "Piglets from mothers with high antibodies against PCV-2 did not develop PMWS."
But when diagnosing PDNS, dont rely on the presence of PCV-2 antibodies as pigs can have the virus without having PDNS/ PMWS. Instead use the presence of virus antigen or DNA in tissue from lesions for diagnosis, he said.
• Porcine circovirus-2 implicated.
• Immuno-stimulation effect.
• Sows may have antibodies.