Fecal shedding and antibody response in four PEDV infected swine breeding farms

Porcine epidemic diarrhea virus (PEDV), a member of the genera Alphacoronavirus in the family Coronaviridae, causes an acute and highly contagious enteric disease characterized by severe enteritis, vomiting, watery diarrhea and high mortality in seronegative neonatal piglets. In the last years, PED caused significant economic losses in swine industry in Asia and United States and since 2014, PEDV has also re-emerged in Europe. Two main PEDV variants circulate worldwide but the so-called S-INDEL variant, considered a mild strain, is the prevalent among the European countries. To gain insight about pathogenicity, viral loads and antibody response, temporal patterns of shedding of the S-INDEL variant were evaluated in naturally infected piglets from four different outbreaks.

A longitudinal study on 4 breeding farms, naturally infected with the PEDV S-INDEL variant, was conducted between January and September 2015. Clinical data, fecal swabs and blood were collected from 30 newborn piglets at 15-30 days intervals during 2-4 months. A quantitative Real time PCR (qPCR), targeting the spike gene, was applied to determine viral loads. A competitive MAbs-based antibody ELISA test was used to detect antibodies to PEDV.

In all the farms, diarrhea was observed in sows in gestation and in the farrowing unit. Mortality in piglets in the 4 farms was 10%, 25%, 40% and 50%, respectively. Percentage of PCR positive animals varied greatly from the beginning (58-100%) to the end (0%) of the study period. Clinical signs were present in 96% of PCR positive animals. Viral load in suckling pigs at 3-6 days from birth ranged from 9.2 to 3.5-log genome copies/gr. After 2-4 weeks post infection only few piglets still showed detectable levels of virus and clinical signs. The 46% of the sows showed anti-PEDV antibodies at delivery but only few piglets (3%) showed detectable antibody and absence of clinical signs at 3-6 days of age. Most of the piglets in the four farms developed antibody responses within 3 weeks of age and they remained stable till the end of the study (60-100 days of age).

Different PEDV circulation profiles were observed within the four infected farms, probably due to the different infection starting time.

Quantitative PCR, clinical records and serological monitoring showed to be useful tools to understand the dynamic of PEDV infection and could be used to implement appropriate control measures.

Disclosure of Interest: None Declared.