The swine farm initially reported concerns of increased lameness in a pen of group housed replacement gilts, as well as a slight decrease in feed intake (day −2 PO). Day −1 PO, lameness and decreased feed intake was more prevalent among the rest of the sows in the herd. Vesicular lesions were observed on day 0 PO, consisting of un-ruptured vesicles on the snouts and feet of approximately 5–10% of the animals on site 1, and the state veterinary office was notified. By day 2 PO, nearly 80% of the animals in the herd had detectable vesicular lesions (ruptured and un-ruptured) on the snouts and feet. Lameness, lethargy, and decreased feed intake were the main clinical concerns during this time; however, by 1 week PO, there was noticeable improvement in the clinical signs within the population. At no time was fever a major concern within the herd. In farrowing, there was an increase in pre-weaning mortality from an average of 12% to a high of 22% during the first 7 days PO, and returned to average levels by 2 weeks PO. The majority of the piglet mortality was associated with dehydration due to poor milk production by the sow, and piglets being laid on, potentially due to sow lameness. No other clinical signs were detected in piglets in farrowing, and there were no detectable signs at the nursery barns at any point during or after the outbreak.
The samples collected by the state veterinary office at site 1 on the day 0 PO were negative for SVDv at NVSL while the NVSL and UMNVDL had the same results for FMDv and SVA (negative and positive, respectively). Subsequent, SVA testing only occurred at the UMNVDL through the study.
Sows displayed vesicular lesions on the snouts at day 0 PO, and SVA was present in 33 out of 34 (97%) of the vesicle swabs, with an average cycle threshold (Ct) value of 16 (range = 12–19). At 1 week PO, SVA was present in 34 out of 34 (100%) of the lesion swabs. At 2 weeks PO, most lesions had healed (only few skin tags and ruptured vesicles remained in the population), and SVA detection decreased to 12 out of 34 samples (35%). By 3 weeks PO, all of the vesicular lesions had healed, and no additional samples were collected.
Generally, viremia was detected up to 1 week PO in sows. A single positive sample was identified at 3 and 6 weeks PO (Fig. 2a). At the first sampling (day 1 PO), the Ct values from the sow serum averaged 33.1 (range = 17–36). Viremia was detected in only 7 out of 34 (20%) of the sows at 1 week PO. SVA 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. Additional SVA positive samples were detected at 3, 4, and 6 weeks PO. In suckling piglets, Ct values averaged 30.6 (range = 24–39.8). Similar to sows, viremia was not detected in 9 out of 30 (30%) of the site 1 piglets enrolled in the study. Viremia was detected in site 2 piglets at 4 (6 out of 30 (21%)), 6 (2 out of 30 (7%)), and 9 (1 out of 30 (3%)) weeks PO, with an average Ct value range of 35.7–38.0.
Tonsil swabs yielded the highest percentage of SVA detection in site 1 sows (32 out 34 (94%)) and piglets (25 out of 30 (83%))(Fig. 2b). In sows, the detection of SVA in the tonsils peaked at 1 week PO (33 out of 34 samples (97%)), with average Ct values of 24.8 (range = 20–27). In site 1 piglets, the peak shedding of SVA occurred at day 1 PO, with average Ct values of 27.1 (range = 20.3–34.6). The detection of SVA shedding decreased over time in sows and piglets, and a single sow and piglet tested positive at 9 weeks PO (Ct values of 35 and 36, respectively). SVA was only detected in 2 of the 30 piglets (7%) from site 2 at 5 weeks PO.
The peak of SVA detection from rectal swabs in sows (31 out of 34 samples (91%)) occurred at day 1 PO and continued to steadily decrease and was not detected at 9 weeks PO (Fig. 2c). In site 1 piglets, the detection of SVA peaked at 1 week PO when 27 of the 30 samples (90%) tested positive. While the detection of SVA decreased in site 1 piglets at 2 and 3 weeks PO, 19 out of 30 samples (64%) of the rectal swabs were positive at 4 weeks PO. At 6 weeks PO, the detection of SVA was same for both site 1 and 2 piglets (11%, n = 3); however, a single piglet from site 1 was still shedding SVA at 9 weeks PO.
The oral fluid and serum samples were positive for SVA from site 5, but negative from site 3 and 4. SVA was detected in 9 out of 10 (90%) of the serum samples (Ct values averaged 32.8, range = 31.8–35.9), and the single oral fluid sample had a (Ct value = 24.3), despite the fact that there were no obvious detectable clinical signs in site 5. Of importance is that site 5 appears to have received SVA positive weaned pigs from site 1 before the detection of clinical signs of decrease in feed intake and vesicular lesions.