Shedding patterns detected by PCR in sows and piglets of Senecavirus A from an infected U.S. swine breeding herd

The objective is to determine patterns of viral shedding, detected by PCR, from dams and their piglets for Senecavirus A (SVA) in serum, feces and oropharyngeal swabs for a 6 week time period post clinical onset.

A 4,000 head breeding herd developed clinical signs consistent with vesicular disease in sows and significant increases in neonatal mortality associated with the presence of SVA. Clinical signs were prominent in farrowing rooms with piglets less than 7 days of age. Clinically affected litters ranged from 30-40% of the litters in these rooms. Clinically affected litters were defined as the dam showing clinical signs and/or the litter having high neonatal mortality. In order to determine viral shedding and viremia, 11 affected and 11 unaffected dams and piglets were selected. For each affected litter, the dam and 2 piglets were tagged and sampled. For every unaffected litter, the dam and 1 piglet was tagged and sampled. For each sow and piglet tagged, serum, an oropharyngeal (tonsil) swab and a rectal swab were obtained. Samples were collected weekly for a period of 6 weeks and were tested by qPCR for SVA at the ISU VDL. A Ct of < 38 was used as the cutoff for calling a sample positive.

PCR results after the first week of the clinical outbreak demonstrated the prevalence of PCR positives were fairly low in sows and pigs (10-30%) and only slightly higher when comparing clinically affected dams and piglets to non-clinically affected. Tonsil and rectal samplings were positive in about half the dams that were clinically affected, while only about 1/4 were positive in non-clinically affected dams. Piglet tonsil samples were positive in about 1/3 of the samples collected, regardless if they were in clinically affected litters or not. Rectal samples were positive in about half of the non-clinically affected piglets, where they were positive in only 1/3 of piglets. Most serum positive piglets were also positive in tonsil and fecal samples. The dam results were more variable in terms sample type. Virus was detectable in serum for a period of 3 weeks post outbreak in both sows and their piglets, demonstrating a relatively short viremia. A high frequency of shedding was detected in tonsil and rectal swabs out to 4 weeks post outbreak.

During the initial outbreak, PCR positive samples for SVA could be found in both clinically and non-clinically affected dams and their piglets. There appeared to be a slightly higher prevalence in clinically infected dams and their litters. Based on these PCR results, SVA viremia lasts for a period of 3 week in piglets and sows and virus is shed for 4 weeks.

Disclosure of Interest: C. Rademacher Conflict with: Swine Health Information Center, D. Linhares Conflict with: Swine Health Information Center, P. Pineyro Conflict with: Swine Health Information Center, P. Canning Conflict with: Swine Health Information Center, D. Holtkamp Conflict with: Swine Health Information Center, L. Karriker Conflict with: Swine Health Information Center.