Results of oral fluids on Dutch PRDC pig farms: prevalence of respiratory pathogens

The objective of this study was to investigate the prevalence of different pathogens in PRDC problems on Dutch pig farms by using OFs with PCR testing for different pathogens.

11-05-2018


Article by:

N. Wertenbroek

Boehringer Ingelheim The Netherlands

Introduction

PRDC (Porcine Respiratoiry Disease Complex) diagnostics can be easily performed using ropes for Oral Fluids (OFs) as testing material. It is a relative cheap, easy and non-invasive method to collect saliva samples in pens with clinical problems. Combined with PCR it gives more insight in pathogens that are present at the time of clinical signs. The objective of this study was to investigate the prevalence of different pathogens in PRDC problems on Dutch pig farms by using OFs with PCR testing for different pathogens.

Materials and methods

In the period of 2015 and April 2017 samples were collected in farms with respiratory problems in nursery as well as fattening pigs. Ropes were placed at 3 age groups at sampling date: “T 0” was the age group were the onset of acute cough was present; ”T -2” was the group 2–4 weeks younger than the acute coughing group and “T +2” was 2–4 weeks older than the acute coughing group. The age of pigs sampled ranged from weaned pigs till slaughter, depending on the onset of the clinical signs. Oral fluid samples were collected with ropes, which were placed in the pens for 20–30 minutes1. Samples were shipped overnight by carrier to the diagnostic lab.
The samples were analyzed by a multiplex PCR (IVD-GmbH lab Hannover, Germany) for PRRS, Influenza, PCV2 and Mycoplasma hyopneumoniae. Results were reported as negative or positive for the respective pathogen.

Results

In total 198 samples were collected from 31 farms. The results of the samples were assorted into 5 age groups: 4–6 weeks (n = 26), 7 – 9 weeks (n = 35), 10-13 weeks (n = 39), 14-18 weeks (n = 54) and 19 – 24 weeks of age (n = 44). In these farms with respiratory problems different dynamics for the investigated pathogens were observed (fig 1). For PRRS the peak of prevalence (61% of investigated samples) was in the age groups of 10–13 weeks, but closely followed by the age groups 14 –18 weeks (57 %). Influenza was most found at 4 – 6 weeks (62 %), followed by 54 % in age groups 7-9 weeks. The highest prevalence for M hyo was found in the late finishing group at the age of 19 – 24 weeks (27 %) followed by 14 –18 weeks (22 %). In the other 3 groups it ranged between 2 and 10 %. For PCV2 the peak was found at 14 –18 weeks (56 %).

Fig 1. Percentage positive oral fluids of different pathogens for the different age groups

Fig 1. Percentage positive oral fluids of different pathogens for the different age group

Discussion and conclusion

A positive PCR primarily indicates the presence of the pathogen but not necessarily proves clinical disease. With this study we demonstrated the dynamics of the pathogens, where they predominantly can be found and where they are spreading most. The investigated pathogens demonstrated different dynamics: Influenza was found primarily in (the first half of) the nursery phase. This demonstrates the role of nursery pigs as a reservoir for the permanent circulation of this pathogen on the farm. This finding is in line with others2,3. The prevalence of PRRS is increasing from weaning to the first phase in finishing. This was expected: PRRS is slowly spreading in the nursery and after mixing by the set-up of the finishing phase, this gives rise to higher incidence during the first 4 to 6 weeks of finishing phase. The same dynamics is shown for PCV2. The results for Mycoplasma hyopneumonia shows its role in nursery is very limited and the dynamics gives a clear indication that the real spreading takes place in the second half of finishing (from 14 –18 weeks onwards). Also taking into account the slow spreading of the bacteria4,5. These results are in line with other recent Dutch results6,7,8.

References

1. Prickett et al. 2008.JSHAP p 86-91
2. Torremorell, 2012. Transbound Emerg Dis doi:10.1111/j.1865-1682.01300
3. Geurts IPVS 2016 p596
4. Fano, IPVS 2004 p187
5. Meyns et al 2006, Vaccine24, 7081-7086
6. Groenland IPVS 2014 p414
7. Dongen et al. IPVS 2016
8. Van Groenweghe ESPHM 2013

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