- 10 minutes
- Expertise article
I. Hernández-Caravaca1, A. Celaya1, S. Figueras1, G. Abella1, E. Sánchez1, V. Rodriguez1
1Boehringer Ingelheim Animal Health España S.A.U.
Introduction
Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the leading swine pathogens1. It is well known that the air temperature and its humidity are crucial to the PRRSV survival. Some studies have identified a correlation between a new PRRSV infection and the season in type 2 environment2,3. The intensive PCR diagnosis effort done by Boehringer-ingelheim animal health Spain, to reveal PRRS herd’s status since 2015, has generated a huge database to work with. The sequencing of these positive samples is provided whenever the veterinarians report clinical signs or changes in the PRRS status.
Thus, the aim of this study is to report the evolution of the % of PRRS detection by PCR and the % of sequences done, and try to link it with the temperature in a type1 environment during different periods of the year.
Materials and Methods
This study is a compilation of the PRRS diagnoses since December 2015 to November 2019. The periods have been divided in thirds (T): T1 was considered from December to March, T2 from April to July, T3 from August to November. To calculate the Spanish mean temperatures by third, the 6 closest weather AEMET stations to the pig production were used. Samples submitted by twelve companies, that were consistently tested in sows and nurseries, were included to calculate the % of positive samplings. A total of 2818 samplings was included. A sampling was considered positive, when at least one sample was positive by PCR. To calculate the % of sequences by T, we used BI Spanish database (2430 sequences) coming from 102 different companies. According to the variable under study, regression analysis, chi-2 test and comparison of means was conducted and a p<0.05 set up as discrimination level.
Results and Discussion
The proportion of positive samplings by T were 43% for T1 and 39% for T2 and T3. No statistical differences were found in terms of % of diagnosis but a tendency (p=0.08) was observed for T1 with regard to T2 and T3 (Fig1).
Figure 1: Percentages of positive samplings samples by T from 2016 to 2019. The red line shows the T mean temperature.
The percentage of sequences done in every T was 42% for T1, 33% for T2 and 25% for T3, finding no statistical differences but T3 tended (p=0.07) to have the lowest percentage. These sequences were only performed when clinical signs or changes in the farm status were detected. With regard to the degree of association between the mean monthly temperature and the percentage of sequences obtained by month we found a negative correlation (p=0.02; R2=19.12) more sequences with lower mean temperatures (fig. 2).
Figure 2: Relationship between the amount of sequences by month and the corresponding mean temperatures.
Conclusions
Comparing the percentages of positive diagnosis and sequences by third, no statistical differences were detected but a tendency to higher values was observed for T1.
There was a negative correlation between mean monthly temperature and number of sequences found.
References
- E. Mateu et, al; Virus research 2006
- Holtkamp DJ, Yeske PE, Polson DD, et al. A prospective study evaluating duration of swine breeding herd PRRS virus-free status and its relationship with measured risk. Prev Vet Med 2010; 96:186–193.
- Steven J. P., Tousignant, Andres M. Perez, James F. Lowe, Paul E. Yeske, Robert B. Morrison. Temporal and spatial dynamics of porcine reproductive and respiratory syndrome virus infection in the United State. Am J Vet Res. 2015 Jan;76(1):70-6
- https://opendata.aemet.es