Which wipes are better to detect flu: udder skin or nasal wipes?

This is our Friday rubric: every week a new Science Page from the Bob Morrison’s Swine Health Monitoring Project. The previous editions of the science page are available on our website.

This week, Dr. Albert Canturri from the Torremorell lab is sharing results on a study looking at udder skin wipes and piglet nasal wipe to detect swine influenza.

Key points

  • Various wipe types can be used to sample IAV from the udder skin of lactating sows. Although differences between wipe types were not seen, wipes that were wet provided a better detection rate than dry wipes. 
  • Furthermore, wiping the nose of 5 piglets within a litter resulted in higher litter detection rates than sampling the udder directly. This indicates that within litter prevalence is a driver for IAV detection using wipes. 
  • Future steps are needed to assess differences in virus isolation among sampling procedures.


Non-invasive group sampling strategies such as the collection of udder skin wipes are increasingly used in active influenza A virus (IAV) surveillance programs in breeding herds. Nasal wipes have been used as an individual sample in piglets, but they have not been adopted widely as a group sample where sampling different animals of the same litter occurs with the same wipe. The objectives of this study were to compare the detection rates of IAV by rRT-PCR among five different types of udder wipes and evaluate the detection rate of udder wipes compared to a composite sample of nasal wipes obtained by sampling five piglets.

Materials and Methods

Five types of wipes with different fabric substrates and liquid media combinations of gauzes and liquid media were prepared as depicted in table 1. Thirty litters per wipe type were selected (n=150 total) and selection of litters was done by systematically selecting litters within a farrowing room. Samples were collected by wiping the underline of sows between 3 and 6 days prior to weaning. In litters sampled with the MEM based media, an additional nasal wipe was obtained from 5 piglets in the litter selected randomly.  After collection, all samples were refrigerated, transported to the laboratory and tested individually by rRT-PCR to detect the IAV matrix gene. Results were considered positive when cycle threshold (Ct) values were ≤ 35 and differences were compared using the Pearson’s Chi-square test.

Table 1. Composition of the 5 different types of wipes depending on their fabric substrates and media combinations


Out of the 150 litters sampled, 64 tested positive (43%). The wipe type that yielded the highest proportion of positive litters was the MEM-based media wipe (16/30; 53%), followed by Swiffer (15/30; 50%). The wipe that yielded the lowest proportion of positive litters was the dry wipe (9/30; 30%), as shown in table 2.

Table 2. Detection rates and average Ct values among the five different types of wipes.

However, differences among wipe types were not significant (p-value = 0.38) and there were no differences between average Ct values of positive samples or the parity of the sow. In addition, detection of IAV positive litters was significantly higher when using the composite sample of nasal wipes collected from 5 pigs (27/30; 90%) than using udder wipes (16/30; 53.3%) (p-value < 0.01), as detailed in table 3.

Table 3. Detection rate differences using udder or nasal wipes within the same litters using MEM-based media wipes