Longitudinal study of Senecavirus shedding and viremia in sows and piglets

How long do sows and piglets shed Senecavirus A after a clinical outbreak? How long is the viremia? Those are the questions answered in this case study of a Senecavirus A outbreak in one US farm.

Objective and Methods

Senecavirus A is a challenge for producers and veterinarians because of its clinical similarity to Food and Mouth Disease (FMD). In this study, 34 sows and 30 individual piglets from 15 different litters were sampled at day 1 post-outbreak and later at 1, 2, 3, 4, 6, and 9 weeks post-outbreak (PO). Serum, and tonsil, rectal, and vesicular swabs were collected for all of the pigs included in the study. The objective of the study was to explore the viremia and shedding patterns in those infected animals. All samples were submitted to the University of Minnesota, Veterinary Diagnostic Laboratory to be tested by PCR.

longitudinal study of senecavirus figures Tousignant 2017.gif
Percentage of serum (a), tonsil swabs (b), and rectal swabs (c) positive for Senecavirus A. Clinical outbreak happened in sow farm 1 (S1) and piglets from sow farm 2 (S2) were mixed with piglets from S1 at weaning.

 

Results

Vesicular lesions were seen in sows only for 2 weeks and had the highest amount of virus. In sows, the detection of Senecavirus A in tonsil and rectal swabs was greater than 90% at 0 week PO and remained as high as 50% through 5 weeks PO. Generally, viremia was detected up to 1 week PO in sows but it is important to note that viremia was not detected in 11 out of 34 (32%) of the sows at any point during the study. Viremia was detected in 18 out of 30 (60%) and 19 out of 30 (63%) in the suckling piglets from site 1. Similar to sows, viremia was not detected in 9 out of 30 (30%) of the site 1 piglets enrolled in the study.

The detection of Senecavirus A in sows tonsil swabs peaked 1 week PO (94% positive) whereas it peaked at day 1 PO for piglets (83% positive). The detection of virus shedding decreased over time in sows and piglets, and a single sow and piglet tested positive at 9 weeks PO.

The peak of Senecavirus A detection from rectal swabs in sows (91%) occurred at day 1 PO and continued to steadily decrease and was not detected at 9 weeks PO. In site 1 piglets, the detection of SVA peaked at 1 week PO (90% positive). 64% of the rectal swabs were positive at 4 weeks PO in site 1 piglets. At 6 weeks PO, the detection of Senecavirus A was same for both site 1 and 2 piglets (11%); however, a single piglet from site 1 was still shedding SVA at 9 weeks PO.

Discussion

The study assessed the shedding pattern of SVA in sows and piglets during an outbreak on a farm in the US and investigated the spread of SVA between pigs during the post weaning period. Vesicular lesions were seen in sows only for 2 weeks and had the highest amount of virus. In sows, the detection of SVA in tonsil and rectal swabs was greater than 90% at 0 week PO and remained as high as 50% through 5 weeks PO, these sample types should be collected and submitted, in addition to vesicular lesion swabs and fluid (if present), as part of FAD investigations for the detection of SVA.

 

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longitudinal study of senecavirus Tousignant 2017

Abstract

Background: The study highlights the shedding pattern of Senecavirus A (SVA) during an outbreak of vesicular disease in a sow farm from the South-central Minnesota, USA. In this study, 34 individual, mixed parity sows with clinical signs of vesicular lesions and 30 individual piglets from 15 individual litters from sows with vesicular lesions were conveniently selected for individual, longitudinal sampling. Serum, tonsil, rectal, and vesicular swabs were collected on day 1 post outbreak, and then again at 1, 2, 3, 4, 6, and 9 weeks post outbreak. Samples were tested at the University of Minnesota Veterinary Diagnostic Laboratory for SVA via Real Time Polymerase Chain Reaction (RT-PCR)
Results: In sows, vesicular lesions had the highest concentration of SVA, but had the shortest duration of detection lasting only 2 weeks. Viremia was detected for 1 week post outbreak, and quickly declined thereafter. SVA was detected at approximately the same frequency for both tonsil and rectal swabs with the highest percentage of SVA positive samples detected in the first 6 weeks post outbreak. In suckling piglets, viremia quickly declined 1 week post outbreak and was prevalent in low levels during the first week after weaning (4 weeks post outbreak) and was also detected in piglets that were co-mingled from a SVA negative sow farm. Similar to sows, SVA detection on rectal and tonsil swabs in piglets lasted approximately 6 weeks post outbreak.
Conclusion: The study illustrates the variation of SVA shedding patterns in different sample types over a 9 week period in sows and piglets, and suggests the potential for viral spread between piglets at weaning.