The SERASCA®-test, improved roundworm diagnosis!
Despite the fact that many studies have previously described the negative impact of Ascaris infections on the pig production system, few farmers actually seem to know to what extent their herd is infected with this parasite. Now, with the development of the SERASCA®-test, a new and improved method is now available for the diagnosis of Ascaris infection pressure in fattening pigs.
High Sensitivity & Specificity!
The diagnostic sensitivity and specificity, as well as the cut-off of the SERASCA®-test were determined using sera from 190 piglets that were experimentally infected with roundworm eggs during 14 weeks. Serum and faecal samples were analysed at the start of the experiment, after 7 weeks, and at 14 weeks. Figure 1 shows the results of the analysis of the serum samples on the SERASCA®-test. The cut-off value for the discrimination between Ascaris-positive and Ascaris-negative pig sera was set at ODr = 0.500 (dotted line). Using this cut-off on the test samples, the test showed a sensitivity of 99.5% and a specificity of 100.0%.
Figure 1:The box-plots display the distribution of ODr levels produced on the SERASCA®-test by serum samples of 190 pigs 0, 7 and 14 weeks after trickle infection with A. suum. The horizontal dotted line indicates the cut-off value of ODr = 0.500.
Better than EPG!
For the detection of A. suum eggs in the faeces, the quantitative McMaster test is usually applied. The results of this examination are reported as number of parasite eggs per gram of faeces or EPG. Important to know is that the EPG levels are not representative for the amount of migrating larvae the pig has been exposed to during the course of its life since the number of worms that eventually develop into adults is generally inconsistent and independant of the intake of infective stages.
Although coprological examinations are easy to perform and require relatively cheap materials, the performance of the sampling and the tests are time consuming and not cost-effective nor optimal for the screening of a large number of samples. In addition, the chances of false positive and false negative results is significant!
False positive results:
- Coprophagia / geophagia
(EPG<200 can be considered false positive)
False negative results:
- Sampling during first 6 weeks of infection.
- Only worms of a single sex present in the intestine.
- Natural expulsion reaction has expelled
larvae before adulthood.
Figure 2: A. suum eggs detected in faecal
sample by McMaster method.
Comparison of the percentage seropositive pigs with the percentage of pigs excreting A. suum eggs after 7 and 14 weeks of infection showed that the percentage of seropositive pigs was notably higher than the percentage of pigs excreting A. suum eggs on both time points (Table 1).
Table 1: Percentage of pigs from the experimental infection experiment in which A. suum infection was detected after coprological (McMaster) or serological analysis (SERASCA®-test).
Better than % affected livers!
In the slaughterhouse, the number of pig livers that show the so-called "white spots" is usually recorded. These white spots are formed by the host as a reaction to the migration of larval parasites. The percentage of livers that show these kind of lesions can therefore reflect recent exposure to Ascaris. When liver white spots are detected, it is highly likely that the pig has undergone an Ascaris infection (Figure 3).
However, the number of lesions and/or the number of affected livers is not representative for parasite exposure! A couple of weeks after infection, the white spots resolve again. furthermore, the pig develops a natural immunity preventing new larvae from completing their migration and therefore forming new white spots. Because of this, the number of affected livers seems insufficiently reliable as a diagnostic method and usually underestimates the true infection intestity in a barn.
Figure 3: A condemned liver covered
with white spots.
When the percentage of damaged livers from 20 Flemish pig farms was compared with the results after analysing blood samples on the newly developed SERASCA® test. Although we found that on most farms between 0 and 10% of the livers were affected, the results of the serological test clearly indicate that on many of these farms with low % of affected livers, there was indeed a significant roundworm infection present!
These results confirm previous indications that the use of percentage of affected livers can significantly underestimate the true Ascaris infection pressure on a farm.
Figure 4: The relation between the percentage of damaged livers and the SERASCA®-test results from 20 examined Flemish pig farms.
Link to PDF with more in-depth information on the diagnosis of ascariosis.
PDF to the paper explaining the development of the SERASCA®-test
